Purified water today has a totally different meaning. It means that it not only has been filtered, but that it has had the ions removed. My first post on this forum was a thread on coolants which will be updated shortly after I can get a friend of mine who is a Lincoln Service Manager for a Lincoln Dealer gives me some input. My post is from the perspective of a PhD chemist. You would be well advised to look at it and educate yourself. Use of anything other than fully deionized water/distilled water is not recommended under any circumstance for any length of time. If tap water is used, your coolant should be flushed at the first possible place you can get it done and get the other repairs to the cooling system completed that necessitated the use of tap water in the first place. Water can contain a large amount of salts that you cannot taste directly but are still there! Ergo, use distilled water only unless you enjoy spending large amounts of money later replacing aluminum parts like your heads when they begin to leak due to corrosion.

No, they aren't. A 4.3 Mercruiser, for instance, is nearly identical to the 4.3 in the Astro van, s10, Blazer, etc on the street

Because it contains various metals and chlorine. This leads to scaling and corrosion of the engine block. Chlorine can corrode stainless steel.

Please find me a label stating you can use tap water. If you look on the back of any coolant bottle it says distilled water.

I was under the impression you meant something other than pleasurecraft.

Also, NONE of those recommend use of salt water. They also recommend use of distilled water, once again, not tap water.

uh.... a freshwater boat powertrain is cooled by the lake/river water you are motoring in, straight up, no treatment. There is no 'recommendation', distilled, tap, or otherwise.

I'm not debating the silly coolant discussion, just pointing out that the whole boat comment was flat out wrong. Boat engines = car engines, minus emissions equipment.

The boats I've been on used an enclosed cooling system. Did the older ones not?

They've always been 'open' for fresh water, as in the water we treat for the tap. A closed system is for salt water boats. And no, nobody is talking about driving to the Pacific so they can use some of that 'crystal clear' ocean water for their cooling system.

I know boats have heat exchangers which are open to fresh water, but those have to serviced every once in a while, and in some cases, replaced. I don't know of any boats which cool the engine themselves with fresh water.

Yeah there goes that tolerance thing again which now days is used about 99% of the time in place of clearance, which is TOTALLY different...

BTW AFAIK, neither tolerance nor clearance have any bearing on the cooling system...

The car companies in order to get more efficient cooling have gone to smaller orifices in the radiators used in our cars. These smaller diameter holes are more susceptible to clogging from lime scale build up. There is a series of reactions showing how carbon dioxide in the atmosphere is dissolved and forms carbonic acid in the coolant. Any metal ions present will then salt out with the carbonate ion from carbonic acid and form boilerscale/limescale. Given this, limiting use of tap water which does contain metal ions is important. In addition some of the metal ions dissolved in tap water will react with the buffers in the coolant deactivating the buffer chemically. Ford recently in their late model cars has seen issues and warranty recalls over coolant systems that have added tap water to the coolant.

But I agree with the fact that engine tolerances for the combustion and other related components have no bearing on the coolant system. But I will note that in more modern boat designs, even though cooled with lake water, etc. there is still a captive coolant system in place that exchanges heat with the environment (lake water). Given this, more modern engines which contain aluminum and iron need to protect the engine from corroding beyond repair. Most people would be upset if they had to buy a $5000 engine every year due to how fast aluminum and iron react when not protected from corrosion.

If you live in a freshwater dominant area, majority of boats are cooled with raw lake water. No closed system - lake water straight through the engine.

Here's a typical mercruiser, one of the most common (consumer) drives on the water

LOL with salty or silty water Here they recommend flushing up to EVERY USE http://www.boatfix.com/merc/servmanl/13/13a6r2.pdf Lots of threads talking about closed loop systems as many aluminum head inboard engines are coming out vs the old cast iron Chevy small block, 4.3 V6 or inline 4 cyls grow out of fashion

Yup. Raw water cooling really isn't supposed to be used in sea water. No problem in fresh water, though. The engines will outlast the boat on the Great Lakes, for example


The old iron engines are obviously growing out of fashion... GM won't produce them forever, just for Merc.

It looks like no one has explicitly mentioned the galvanic response that results in the rad and heater core getting eaten away. That's my biggest concern.

IPreferDIY - The coolant minimizes the galvanic reaction, but there will be minor galvanic action on the aluminum parts. Eventually that's what eats the heat core and radiator. Only way to eliminate that is to somehow mount some sacrificial zinc anodes into the coolant.

The ocean-cooled marine engines use "zinc pencils" which thread into the thermostat housing. They get replaced annually. They're about $5 each.