Dear fellow car lovers,

I owned a 97 mercury grand marquis with the handling package that was destroyed by a driver that rearended me at 40 mi/hr when I was at a dead stop. My replacement car was a 2001 Lincoln Town Car Cartier L. Due to lack of engine coolant maintenance I was forced to replace my head gaskets on my 4.6L engine. I did a little research on coolant types and found the following. For reference you might want to check the website for Zerex brand coolants and Caterpillar Tractor company's pamphlets on fluid types. Yes you saw right Caterpillar. I will explain in a moment.

I am a scientist with a Ph'D in chemistry and do understand coolants since chemists deal with materials. The best coolant for heat transfer is water for your engines. This statement is verified both in the physical properties of water and by engineers who have tested water as a heat transfer fluid. But water has 2 problems with it that argue against using only water as a heat transfer agent.

1. Water, being a "universal solvent", will disolve many things. Engines have surfaces of copper, iron, aluminum, tin, and other metal alloys that make up the engine. Since salts will develop over time due to disolved carbon dioxide (carbonic acid) in water and heat, when water is in direct contact with these metal surfaces, corrosion will develop and engine damage will result.

2. Water also expands when it freezes and will cause cracking in the block and heads when it freezes.

To deal with the freezing problem very early in coolant history, methanol and ethanol mixtures with water were used. This is a problem since both alcohols will burn quite nicely and will lead to problems with fires. An alternative was found though with the substitution of ethylene glycol mixtures with water as a freezing point depressant in mixtures with water. This has been so successful that this type of coolant mixture predominates in the market today and has been used with variations for over 70 years. However for some who may be environmentally concious, propylene glycol is marketed as a substitute antifreeze but is not recommended by any engine manufacturer in existence today. The reason is heat transfer. Water, with an arbitrary heat transfer value of one, compares with ethylene glycol with a heat transfer capacity about half as much as water with propylene glycol having a heat tranfer capacity of one quarter that of water. Modern engines create tremendous amounts of heat and the coolant is needed to conduct the heat away from parts that may melt, bend, or warp when exposed directly to the heat of burning gasoline.

If you notice I said nothing about corrosion. Corrosion problems have been noted for many decades in engines which lead to the development of additive packages for coolants. One note however needs to be made here about the color of coolants. Any coolant can be dyed whatever color is desired by the purchaser of the coolant. As a result, do not rely solely on the color of the coolant to tell you the type of coolant. Also in discussion with a Zerex representative about coolants it was mentioned there is no "universal coolant" with a corrosion additive package that is compatible with all coolants. So do not get caught in this trap.

This said there are 4 different types of coolants with additive packages that are not cross compatible with each other. However all of the coolants contain ethylene glycol for freeze suppression and some sort of buffered basic salt additives for corrosion inhibition. I will name the coolant types in order of use.

1. The first is called Inorganic Acid Technology (IAT). This type of coolant has been around for many decades and works quite well when maintained. This is used both in cars and in heavy trucks with different levels of anticorrosion inhibitors used depending on application. Since silicate salts are a major substituent in these coolants most of these coolants are opaque due to the undissolved silicates in the coolant. This, plus depletion of the corrosion protection additives over a relatively short period of time, requires this type of coolant to be changed every 2 years. This type of coolant is used in all pre 2001 Ford products with the exception for Dexcool as noted below.

2. The next type is Dexcool. This coolant is an organic acid technology coolant (OAT) and was developed by GM for extended service intervals. Ford did try this out in one of there vehicles for 1999 but found so many problems with this type of coolant they discontinued use of this coolant. The main problem is that this coolant uses 1,4-benzenedicarboxylic acid as one of the buffer constituents in the coolant. Coupled with ethylene glycol in the presence of oxygen and metal oxides, this will form a brown sludge in the coolant. Every mechanic including former GM mechanics recommend flushing and changing to a different coolant type AS SOON AS POSSIBLE. As far as I know, you must not use any coolant that is Dexcool or Dexcool compatible in your vehicle under any circumstances.

3. The third type is the G-05 spec coolant. This coolant uses a Nitrated Organic Acid Technology (NOAT) additive package. This type is used by Ford, Chrysler, Audi, and Mercedes Benz among others. This is a good coolant but needs servicing every 3 years. You will find this in all 2001 and later Ford products.

4. The forth type is Caterpillar's EC-1 specification coolant. To meet this specification you must test 6 engines for 6000 hours of use with at least one engine having a radiator with an aluminum core and one engine having a copper/lead solder core. It is required when these engines are finished testing you test both the coolant and tear apart the engine to note any wear/corrosion in the engine. The specifications are writen so tightly that to pass essentially you should have no corrosion or wear in the engine. When I asked a Caterpillar representative about use of their coolant type and did they see any coolant related issues their answer was no if all their recomendations are followed to the letter. This unique coolant will last for up to 6 years or 600,000 miles if you follow Caterpillar's recomendations. Since they build engines for 24/7 operation with little downtime for maintenace, this is a big thing they have done to improve reliability of their product.

All coolants use water for dilution to get the freeze protection. Common dilutions are a 1:1 ratio glycol/water for -34F freeze protection or 3:2 ratio of glycol/water for -54F freeze protection. All coolant manufacturers and engine manfactures today require the use of distilled water or deionized water in their coolant mixtures. This is due to dissolved salts in the water from standard tap water, well water, or drinking water that create scale inside the engine block and block the coolant passages. This said the recommended procedure for changing coolant (rarely followed) is below. This procedure will flush any old stubborn dirt (think corrosion) out of the block.


1. Flush old coolant out of cooling system with distilled water until water runs clear. This will take about 20 gallons of water in a Ford Crown Victoria/Mecury Grand Marquis/Lincoln Town Car or other 4.6 liter Ford engine.

2. Drain water in coolant resevoir and radiator and add coolant concentrate to restore 1:1 ratio or 3:2 ratio of glycol/water in coolant.

3. Make sure there is no air pockets left in the engine before running down the road.

To change coolant types from the old green coolant to either the late model Ford G-05 coolant or Caterpillar's EC-1 coolant following the recomendation of Caterpillar for changing from the old IAT coolant to the EC-1 coolant is a good way to go.


1. Flush old coolant out of cooling system with distilled water until water runs clear. This will take about 20 gallons of water in a Ford Crown Victoria/Mecury Grand Marquis/Lincoln Town Car or other 4.6 liter Ford engine.

2. Add Caterpillar coolant cleaner and run engine for 30 minutes. (This cleaner is less harsh on the cooling system and will get your engine clean)

3. Flush cleaner mixture out of cooling system with distilled water until water runs clear. This will take about 20 gallons of water in a Ford Crown Victoria/Mecury Grand Marquis/Lincoln Town Car or other 4.6 liter Ford engine.

4. Drain water in coolant resevoir and radiator and add coolant concentrate (Either G-05 or EC-1 coolant) to restore 1:1 ratio or 3:2 ratio of glycol/water in coolant.

5. Make sure there is no air pockets left in the engine before running down the road.

I used this procedure in my 2001 Lincoln Town Car and have found that I pulled a lot of black sludge out of my engine and now I find the engine warms faster and runs better than before. It is in all cases better to maintain coolant properly than to spend $3000 on a head gasket/intake manifold replacement as I had to do.

Good luck

tl;dr
But skimming the wiki like manifesto:

40 gallons of distilled water! Sure it might be 30 cent a gallon but that would wipe out even the larger grocery stores around here, and the 5 gallons for a buck water oasis places, is RO water good enough?

I don't have a PhD

Death cool = bad

gold/yellow = good

If it had green in it, stick with green or flush (a couple of gallons of distilled water and a shop vac!) and go with gold/yellow.

But you may want to note that Prestone Extended life coolant is a "Dexcool" type of coolant here and it is colored green. Also the use of distilled water may as you say "wipe out the local grocery store". is true. In my case I purchased the water over several trips. You could use a system for production of extremely pure water like a Nanopure laboratory water system but these are $$ to buy and maintain and are more than the back yard mechanic needs. Unfortunantly I have not met many shops that will do this right. I got lucky in that my mechanic would do what was right. We spent about 3 hours on the correct procedure to change from one type of coolant to another. As I said, this is a best practice but is rarely followed.

Also I did omit the following. Make sure you test your coolant freeze protection. If you need to add more coolant concentrate drain coolant from radiator petcock into an empty coolant bottle then add more coolant into the radiator to match the needed freeze protection. Make up some of your own 50/50 mix with the coolant in the bottle you just filled for topping off your coolant resevoir. You will have some left over. I used 2.75 gallons of concentrate here in my project.

In reply to the reverse osmosis water question the answer here is a qualified NO. Reverse osmosis water still contains a significant amount of calcium cations in solution. Calcium cations in the presence of dissolved carbon dioxide (carbonic acid)found in all water will form calcium carbonate that will cause calcium carbonate scales that coat the inside of your engine. This is very bad for your engine because calcium carbonate is a good insulator and this will destroy your engine.

One note here about flushing and removal of chemicals. In chemistry we learn that it takes three washes with an equivalent amount of a clean solvent to thoroughly wash out the prior chemical beyond the point of detection. Since a Crown vic holds about 4 gallons of fluid, at least 12 gallons would be needed if one could totally drain the system. This will not happen because the radiator drain will not drain what is in the engine block or in the heater core. As a result, a 20 gallon minimum flush is needed to get all the old coolant out of the system. In this case more is better.

Thank you. I did not know that propylene glycol is a weak sister to ethylene glycol for heat transfer.

Note that Ford recommends initially changing the G05 at 5 years and 3 years thereafter. The TSB that treats this subject states that the apparent derating is because of the variability of water quality at the service point. It follows that if you use good quality water, distilled or deionized, you should be able to go 5 years after servicing your coolant with G05.

Note also that alcohols are corrosive to metals so that must have been another reason to get away from that as a coolant in addition to the fire hazard and the need for seasonal changeover due to the reduced boiling point of the alcohol/water mix.

What did you find out about the use of phosphate and silicates as corrosion inhibitors? I recall reading that the European manufacturers reject phosphate because of hard water/precipitation issues and the Japanese manufacturers got away from silicates because of abrasion issues. Apparently European water is generally pretty hard. Both are good passive corrosion inhibitors noted for the speed a which they coat metal surfaces. I understand that phosphate is better for iron and silicates are better for aluminum, but I could be wrong. It would be nice to know if the paradigm shift away from silicates and phosphates was influenced entirely by the drive for longer service intervals or if the change from iron, copper and lead to aluminum was a factor.

I seriously question the need to flush with that much purified water. Flushing with tap water (garden hose) followed with 3-4 "fill circulate and drain"s will leave you with 3-6% tap water in the system and only use 6-8 gallons of purified water in these vehicles.


IMHO RO water would be fine. In an open system (without recirculation) I can see how RO water might not be good in a cooling system. (I suspect that it still might go negative on the Langelier Saturation Index in pure form, but I don't believe that it would be very positive.) In a closed system, you might get some calcium carbonate precipitation but when the calcium is gone, it is gone, and you will have no more precipitation.


Note that Bangster lives in a land where the tap water is purposefully brought to the dissolved mineral saturation point by the CRAP, er CAP project. It involves moving the water in mile after mile of open channels so maximum evaporation takes place.

In response to LTDteether's points.

1. Reverse osmosis water (RO water) can still contain significant amounts of dissolved salts in solution. You might not taste them but it still is there. As a result, these dissolved salts interact in a negative fashion with any of the additive packages which shortens the service life of all coolants. This is a bad thing and means RO water is like tap water. The only water that would meet minimum standards would be Deionized water. RO water is not deionized water. Deionized water must meet minimum resistance values approaching that of 100% pure water which suprisingly is an insulator not a conductor. RO water does not meet this standard and must be considered tap water for all intents and purposes.

2. I agree with you about the corrosion with metals and alcohols. I have worked with the formation of compounds having a metal center and various attachments to the metal center. I won't go into all the chemistry that can happen here (lifetimes of studies could be done here still) but suffice it to say under heat and pressure any system will react. The anticorrosion inhibitors in engine coolants need to suppress these reactions in the water/glycol mixtures used in engines.

3. Silicates are preferred by the Europeans and phosphates by the Japanese due to the geology sources of water in those areas of the world. But for varying reasons both the Japanese and Europeans are right that silicates are abrasive and phosphates have precipitation issues. However in an interesting twist for the IAT style coolants here in the USA, both phosphates and silicates are used in varying proportions. The buffered solutions both give quick protection and are thorough in covering all areas in the coolant system. However they are quickly consumed (reacted) and need replacing on a regular basis.

4. The drive to form the new style of coolants was in part to extend the service life of the coolants with an additive package that was more stable in solution. Also the need to limit abrasion of the coolant on the coolant pump is important to extend service life of the engine. The third reason is that today's engines run hotter than yesterday's counterparts to improve efficiency in the engine. A little study into the Carnot heat cycle engine will help this become a little clearer on this point.

5. The flush with distilled water will do two things for you.

a) Dissolve any salts slightly soluble in that will not disolve in regular tap water. This will help clean your coolant system in a more thorough fashion.

b) Allow for ideal conditions to get the maximum life possible out of the coolants used today. This will in part obviate the need to follow the Ford TSB you cite here. If you choose to use tap water here you must follow the Ford TSB recomendations because of the dissolved salts in tap water which will shorten the service life of the coolant.

Also note the second fluid change recomendation was to change from one coolant additive package type to another. In this case being too careful is far better than cutting corners too close. Please refer to my prior post above where I discuss in part the requirements for rinsing a chemical out of a vessel using a solvent that will dissolve that chemical. This requires 3 complete rinses with clean solvent to fully clean a vessel of residual chemical. Since you cannot pull an engine apart to do this easily my recommendation for 20 gallons of distilled water is to be considered a minimum here. Let us know if there is a coolant drain plug in the bottom of the engine block as inquiring minds would like to know. This would lower the amount of water needed by 40%. To my knowledge no engine has a coolant drain plug in the block and the freeze plugs are too high to use as a substitute here.

Hope this answers some of your questions.

Stalag

As Bangster pointed out, some people like to use the wet shop vac to get more fluid out of the cooling systems. I may try it next time.

Yes but that also requires more dissassembly of the engine cooling system here. Are you planning on putting the shop vac on the lower hose? That might get more water/coolant out of the block but you would need to do this 3 times in between making sure all air was out of the system upon refilling after each time you vacuumed out the water. There would still be a fair amount of residual water in the bottom of the block each time you did this. And did you consider the heater core? I could see some merit but you would need to suck water from several places in the engine each time you filled and flushed the system. Although, the use of a shop vac might be somewhat better at getting dirt if when vacuuming out the various sections of the cooling system that the section being vacuumed out is backflushed simultaneously with distilled water(preferentially) or deionized water (okay). Might be more work but definitely thorough.


By the way when I did this my mechanic and I used a coolant flush machine filled with distilled water only. We did not worry about entrained air because of the method we used.

stalag

I'm confused. So the Prestone Extended life coolant I just purchased is different than the green Prestone coolant I use to purchase a couple years ago?

I see that Prestone makes all kinds of coolants . One being "Extended Life" and another being "Dexcool Extended Life".

I know to stay away from Dexcool, but what about just plan Prestone Extended Life. What category does that coolant fall under?

I have not looked at the Prestone stuff for a couple of years. Look at their stuff and see if they say it meets the Ford specifications for either green or G05. It did not used to. The Zerex products, OTOH, do, at least the last time I looked. Go to their web site. The Zerex old fashioned green is really not quite old fashioned. It has reduced silicates compared to what was used in cars long ago. How long ago, I am not sure. The trend in coolants, for a long time has been reduced or no silicates and phosphates. Both are good passive corrosion inhibitors, but the phosphate precipitates with hard water and silicates gel too much after two or three years.

The only places that I know of to get G05 are the Ford dealerships and NAPA (Zerex). I called ALL the auto stores in town to see if I could find some because NAPA tends to be pricy. Someone here, IIRC, reported that Peak also has G05. The only people advertising that they have old-fashioned green-like substance is Zerex.

Is the Prestone and other manufacturers' "all cars under the sun, all models in the world" stuff the same or compatible with the green or gold stuff that came in your car? I don't know. I will stick with the recommended material. I don't want to be wondering if my heater core would have lasted a few more years if I had used the specified coolant. The radiator, I could care less, it is much easier to change.

I will second the answer of LTDteether here. No coolant is a universal application in all cases. The only way would be if it were ethylene glycol only with no anticorrosives in it. Honeywell is the manufacturer of record for Prestone coolants and they are not noted to be a large chemical company or oil company. They do have good products but I would not switch to them directly because I do not think that they are "drop in replacements" for the genuine G-05 spec coolant. I would stick with the known specifications and not trust the claim of "compatible" here. I am still checking into the Prestone coolant types and will let you know more later.


Zerex brand can be found according to a post in a mercedes benz forum quoted as: " Our biggest supplier for the product is Carquest Auto Parts. Other options include Napa, Auto Zone, Advance, O'Reilly's, & Pep Boys. If these places don't carry the product, please just ask them to order it for you"

Peak also does not have a drop in replacement G-05 spec coolant although they claim their "lifetime coolant" can be used as a drop in replacement if the system is flushed/cleaned thoroughly. I suspect to get the "lifetime warranty" you will need to flush/clean the system in a fashion similar to what I laid out in the posts above. This may be more trouble than it is worth unless you are intent on using this coolant only from this point on. I personally have the same reservations as expressed about the Prestone brand above.

Chevron/Texaco does have G-05 type coolant available under the Havoline brand. Visit the Havoline.com website for more details.

But if it were me I would get the G-05 from the Ford dealer or Lincoln/Mercury dealer in your area or find the Zerex G-05 coolant as your best overall choices.

Stalag

So I guess there is no place a normal consumer could get that EC-1 specified coolant, is there?

Any Caterpillar dealer of course will carry truckloads of the Cat EC-1 coolant. But alternatives also exist. I know Zerex EC-1 is sold at napa. You might find it also at larger parts shops that do business with truck parts. You can also buy EC-1 coolant in any truckstop under the Shell or Delo brands. It is highly recommended you follow Caterpillar's recomendations on water quality. This is so stringent that you would be better off using ONLY distilled water or deionized water in these applications. Use of tap water, softened water, or other waters not meeting the specifications outlined in the Caterpillar engine fluid recomendation writeup SEBU6251-12-01 or equivalent publications on engine fluid recomendations IS NOT RECOMENDED and WILL SHORTEN THE LIFE OF THE COOLANT. In fact make sure you read SEBU6251-12-01 AND UNDERSTAND THE SECTION ON ENGINE COOLANTS before deciding to switch to an EC-1 coolant. My recommendations also stand as they mirror Catepillar and expand on the needed amounts of water from a Ph'D chemists studied recomendation after I read this publication and looked at the amount of fluid actually in a 4.6L engine coupled with a recomendation of a mechanic with 40 years of experience with cars.

Cheers and good luck,

stalag

I did further checking on some of my comments in the above posts. I wish to add some further info on what I have since found out.

1. coolant drain plugs do exist on the bottom of our blocks. However it may be difficult to remove these to fully flush the engine block. These were pointed out to me in another post and confirmed in a book on 4.6 modular engines by Sean Hyland. If you do use these for flushing you should be able to do a more thorough job than using any flush machines as far as cleaning the engine's coolant system.

2. About reverse osmosis water. I have found several commercial sources for low contaminant quality water. One source would be Nimbus Water Systems EE series systems or you might want to check into the Nanopure system from Barnstead. These systems are not cheap and if you do not need the water for other purposes this might be too much $. Not all reverse osmosis water systems will meet the needs of no dissolved solids (salt) in the water. If you do not know how to verify this the Distilled water/Deionized water recommendation still stands.

If one wants me to look over specifications for water quality I would be happy to help. PM me with the request.

Cheers,

Stalag

In reply to above I had the chance to check out Prestone extended life coolant. The coolant is a Dexcool variant (for all intents it is dexcool) dyed green. It is not the old style coolant (inorganic acid technology coolant).

Stalag

I'm not a chemist & I didn't stay at a Holiday Inn Express last night. But I wrote this a few months ago, and it relates to this topic. My understanding in item 10 about LL coolant & in item 12 about the bacteria is based on discussions with coolant flush reps, parts store managers, & GM technicians. I don't claim it's a superior explanation to stalag's - it's just what I've heard. I'm adding a link to THIS thread for anywhere else that I post this article.

Engine cooling basics

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I've noticed a lot of questions about the cooling system, and there seems to be a lot of misunderstanding about this seemingly simple system. Even pros don't always grasp the basic concepts about it, so I'm going to try to lay it out. Some of this may seem overly simplified, but I'm trying to make it readable by anyone.

1. Internal combustion engines produce heat by burning gasoline in air. In fact: every bit of energy produced by the engine ultimately becomes heat (the simplest form of energy). Since an engine block large enough to dissipate this heat would be too heavy, and since it's not practical to direct sufficient airflow past the engine, a denser fluid than air is needed to carry it away so that the metals don't oxidize & the lubricants don't combust. Water was the early obvious choice because it's cheap & plentiful, but its relatively low boiling point made it less effective than needed. So chemicals were added to raise its boiling point (any mixture of liquids has a higher boiling point & lower freezing point than any single component); specifically, ethylene glycol (a poisonous alcohol with a sweet flavor). Certain other chemicals are added to inhibit corrosion, lubricate the water pump seals, make the coolant bitter so animals don't drink it, give it color for identification, etc. Some of these additives are consumed over time, requiring regular replacement of the coolant mixture. Additionally, the system is sealed to create higher-than-ambient pressure, which also raises the boiling point. The main benefits of a higher boiling point are that the coolant can carry MORE heat (energy) at a lower flow rate, and the coolant isn't lost as fast as with a vented system. Some early water-cooled vehicles consumed more water than fuel.

2. But the DISadvantage of a liquid cooling system is that it can prevent the engine from reaching operating temperature. So it needs to be regulated in order to allow the engine to get hot enough to vaporize the fuel, boil contaminants out of the oil, maintain proper clearance in the bearings, etc. The obvious regulator is the thermostat. Its purpose is to restrict flow when the coolant is cold so the engine warms up faster. Virtually all thermostats contain a wax pellet with a calibrated melting point. When the wax melts, it expands, generating a force that overcomes a spring which normally holds the thermostat's valve closed. As the valve opens, coolant rushes past, and the wax may cool, allowing the spring to close the valve again. So the flow will "pulse" as the system warms up. Most t'stats include a weep hole to allow a VERY small flow during warmup so that the engine doesn't overheat before the t'stat gets warm. This weep hole also helps to bleed air from the system, and so should always be installed upward. The other regulator is the cooling fan clutch (or relay/PCM/ECT for electric fans). A thermal fan clutch is designed to absorb heat from the radiator & conduct it to a bimetallic coil which operates a lockup mechanism inside a silicone grease bath. When the coil is cold, the clutch is unlocked, allowing the fan to spin slower than then engine & restrict the air moving thru the radiator. As this airstream heats up (due to the engine warming up the coolant), the mechanism links the fan blades to the fan shaft (usually attached to the water pump), which then boosts the airflow thru the radiator. Again, a "pulse" effect can develop under certain conditions. Some early systems without a fan clutch used a flex fan whose blades created very high flow at low RPM, but then flexed forward into a low-flow angle at higher RPM. These were often unacceptably loud, which led to their blades being irregularly spaced to reduce the drone. This irregular blade spacing was carried over into clutched fans, as well as most others, like alternator fans which were noted for "sirening" at certain speeds.

3. Since heat doesn't flow thru liquid fast enough, the liquid must be forced to flow thru the system from the hot area (the engine block & heads) to the heat exchanger (the radiator). The most common method is a belt-driven centrifugal pump, used for it simplicity of design, & general reliability. Most are simply a stamped steel impeller pressed onto a shaft supported by 2 sealed bearings within a cast housing that includes the water inlet from the radiator. Common failures in the water pump include the impeller slipping on the shaft (reducing the flow to almost nothing), impeller erosion due to abrasion &/or corrosion, bearing seals leaking (they're drained thru a hole drilled into the housing), bearing noise, or shaft damage from some external failure (like belt failure or collision). The water pump may be embedded in the block (Ford 300ci/4.9L & modular V8s), embedded in the timing cover (Land Rover 3.9L/4.0L/4.2L/4.6L), attached to the timing cover (Ford 302ci/5.0L & Ford 351W/5.8L), forward of the timing cover (many GM smallblock V8s), or remote (certain VWs).



4. In almost all, however, the coolant flow path is virtually the same: coolant drains to the bottom of the radiator where it flows out thru the lower radiator hose to the water pump inlet. The pump then forces the coolant into the block, where it flows around the cylinders to the back of the block. Cutouts in the head gasket regulate where & how much coolant enters the head & returns to the front of the engine. Within the head(s) is where the coolant reaches its highest temperature, which is why all coolant sensors are near the head(s). In V engines, the coolant flows into a crossover journal in the intake manifold before diverging; in straight engines, it diverges from the head either thru the t'stat or into the heater outlet. In either case, this is generally where its temperature is detected by both the sensor for the gauge & by the ECT for the PCM (EEC). Some V engines also have a bypass hose which allows coolant to return directly to the water pump. There may also be a small circuit to the throttle body for de-icing, which typically returns to the radiator upper tank. Coolant that exits the t'stat flows thru the upper radiator hose into the top of the radiator & thru the core where heat is radiated into the airstream. The cool (lower) radiator tank may contain the upstream heat exchanger for the automatic transmission, and the lower radiator hose may contain an orifice which diverts some coolant to the engine oil cooler.

.
The lower radiator hose flows TOWARD the engine.
The upper hose flows AWAY from the engine.
The heater hose connected to the intake manifold or t-stat outlet flows AWAY from the engine.
The heater hose connected to the water pump flows TO the pump.
The little bypass hose on V8s flows TO the pump.
The metal line on the radiator flows TO the radiator.
Hot coolant flows OUT of the head or intake manifold.

5. In most engines, coolant ALWAYS flows thru the heater core circuit. The outlet to the heater core is beside the t'stat, so the t'stat can never restrict flow to the heater core. This serves 2 purposes: it allows an unrestricted failsafe coolant flow (although the heater core isn't nearly large enough to cool the engine if the radiator becomes restricted), and it allows the cabin to receive heat as soon as it becomes available, irrelevant of the radiator temperature, ambient temp, t'stat, fan, or clutch/relay. Even if the coolant level becomes critically low, the heater circuit will still generally have coolant in it since it takes less coolant to sustain flow within its smaller capacity. In some vehicles, a problem has been recognized in which high engine RPM during warmup can result in excessive pressure within the heater core, resulting in rupture. The fix is to retrofit a slight restriction (an orifice plate) into the circuit upstream of the heater core to limit the flow, and thereby, the pressure. Returning coolant is typically routed directly into the water pump. If the heater core fails, it is safe to loop a hose from the outlet directly back to the return indefinitely. It may also be beneficial to occasionally reverse the hoses at the heater core to keep it flushed out. The direction of flow in the heater core is irrelevant.

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6. As with virtually every substance, the trapped air in the coolant system expands as it is heated by the engine. Up to a limit, this effect is utilized to create the pressure which increases the boiling point. But excess pressure must be vented, without releasing poisonous coolant onto the ground. So a pressure cap is used either on the radiator for a system with a vented overflow tank, or on the "degas bottle" for a fully-pressurized system. The cap has 3 main functions: a) to seal the pressurized portion of the coolant system up to the target pressure; b) to direct the UNpressurized portion of the vented system into the overflow tank; & c) to allow coolant to return from the unpressurized tank into the pressurized system when the system develops a vacuum (during cooldown). This return of vented coolant is dependent on the radiator hoses being fairly rigid, either because of their rubber compounds being stiff, or because of internal springs which support their shape. Hoses that are too soft (often due to oil contamination or just age) will simply collapse, preventing the return of lost coolant from the unpressurized overflow tank. This is just one reason for the increasing use of a pressurized tank (degas bottle) which is designed to hold a specific air pocket within the pressurized system. The air creates a spring that allows for coolant expansion without the risk of coolant loss due to venting; even to an overflow tank. Both systems ultimately allow failsafe venting to the ground.

7. Another refinement to the liquid-cooling system is the fan shroud. Often misunderstood as dead weight or an unnecessary safety shield, the shroud performs an integral function in hi-performance lightweight cooling systems. It vastly improves the fan's efficiency at moving air, as well as assisting the fan in BLOCKING airflow during warmup. Some fan shrouds also include vent flaps which open at high vehicle speed to allow extra air to flow thru the corners of the radiator not sufficiently served by the fan blades. Equally (if not more) misunderstood is the bumper valance. Not merely a cosmetic addition to reduce approach angle - on some vehicles, it is critical to engine cooling. The air-damming effect it produces at high speeds results in a slight vacuum under the engine bay which dramatically increases airflow through the radiator. Without the bumper valance, air can strike the front suspension & bounce up into the engine bay, blocking the radiator's airstream. This same overheating/undercooling effect may be noted if the vehicle is lifted significantly, or if the hood is left open on the safety catch.

8. Possibly the latest refinement to the liquid cooling system is the electric cooling fan motor. More controllable than the thermal clutch, the e-fan allows designers to instantly control the airflow thru the radiator & condenser through the PCM's programming. Using any number of relays & resistors to produce any number of speeds (similar to the HVAC blower motor), engine temperature can be much more precisely regulated, at the cost of slightly higher complexity & weight, with slightly lower efficiency (due to the mechanical/electrical/mechanical conversion of energy). E-fan vehicles require a noticeably larger alternator, and some require failsafe cooling programming in the PCM to protect the engine from fan motor failure. E-fans also have an attraction for off-roading since they allow the driver to turn off the fan before fording deep water, thereby reducing the chance of engine or radiator damage. A common misconception is that the e-fan is somehow more fuel-efficient, but it is inherently LESS so.

9. In typical American fashion, coolant is most often referred to by a misnomer: 'antifreeze'. That characteristic is as much a side-effect as a desirable one. But it IS desirable because water alone would freeze in many climates where vehicles are used, and even WITH antifreeze, this danger is still a cause for concern. So much so that every liquid-cooled engine incorporates freeze plugs to reduce the risk of engine damage resulting from water's peculiar characteristic of expanding when freezing. Ice is so strong that it will crack a mountain of the hardest stone, so a cast iron block doesn't stand a chance without carefully-designed & -positioned freeze plugs to relieve the stress. Steel being cheaper than brass, most factory-installed plugs are the former. Most aftermarket plugs; the latter, due to its corrosion resistance. Temporarary rubber freeze plugs are also available. In some climates, and often for diesels in any climate, some freeze plugs are replaced by a block heater; most often with a common plug for 110VAC household power routed to the grille so that it can be plugged into an extension cord overnight.

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10. Other than collision, the most common cause for coolant leaks & blockages is corrosion. Corrosion is a natural effect of pure metals & alloys being exposed to water, which naturally absorbs oxygen & CO2. It is also caused by dissimilar metals (iron, steel, aluminum, etc.) being in contact with an electrolyte (water with ions), called "Galvanic action". Both of these act continually in varying degrees to eat away at most metal components exposed to the coolant. Pump impeller blades, radiator cores, heater cores, steel pipe nipples, & thermostat housings are susceptible. The results of unchecked corrosion are leaks in the affected parts (usually the thin steel & soft aluminum ones go first) & sedimentation in the radiator, blocking the lower tubes. To combat their effects, various compounds are blended with the coolant. But they don't last forever, especially when the vehicle is NOT operated (stored/abandoned). So regardless of mileage, COOLANT MUST BE CHANGED REGULARLY. And despite its intentionally-misleading name, long-life coolant must be changed on the SAME schedule, if not sooner. The "long-life" terminology only applies to its antifreeze/antiboil characteristics; its corrosion-inhibitors are consumed even faster than standard coolant, making it "short-life" coolant. Another marketing ploy is "ready-mix" coolant, which has gained much popularity over the typical concentrated (half-&-half) coolant previously available. A quick comparison of price (often higher for a gallon of ready-mix than for concentrate) shows that a vehicle requiring 2 gallons of coolant will cost more than twice as much to fill using ready-mix as with concentrate + distilled water.
There's a sucker born every minute - don't be one. Buy only normal-life concentrated coolant, and mix it yourself with distilled water.

11. If you have a leak, don't waste time or contaminate your cooling system with any "trick fixes" like cracking a raw egg or dumping pepper into the radiator. They don't usually work for long (if at all), and they cause problems later after the leaking part is replaced. Just START by replacing the leaky part, and you'll save money, time, & sweat. If you absolutely have to use a temporary fix, use Bar's Stop-Leak, which is a neutralized sawdust tablet.

12. COLOR When GM introduced its ill-fated (like so many other GM innovations) Dex-Cool coolant, it chose to distinguish its product (thankfully) by using an orange dye, instead of the common green. Both colors are intended to be detectable by UV light for tracing leaks, but Dex-Cool's formula failed for 2 reasons: 1) it contains a compound that is apparently very nutritious for certain bacteria, & 2) the tap water used at many GM factories for coolant mixing contained those bacteria. The resulting slime from the flourishing bacteria created an effective glue, which blocked up the coolant passages in the radiators & heater cores, causing mass overheating for several years. The problem has since been eliminated, but the color remained, causing more confusion. Ford went to a yellow dye (also UV-detectable) to distinguish its bittering agent (& a few other chemical changes), and now some aftermarket coolants contain other colors in an attempt to indicate compatibility with certain OE coolants. The typical result is simply MORE confusion, and the only remedy is to carefully read the labelling, since no standard has yet emerged. Ford offers these quick-reference charts as PDFs:

http://www.fcsdchemicalsandlubricants.com/dealer/quickref/scuc.pdf
http://www.fcsdchemicalsandlubricants.com/dealer/quickref/ethylene.pdf

For more info, read these captions:
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