Just wanted to take a moment to share what I've done with my coolant issue. Problem I had was the coolant would always turn dark orange when I used Motorcraft Premium Gold, otherwise known as G-05.

Following Stalag's advice, drained the radiator, and removed the thermostat and upper radiator hose to circulate pure distilled water until it ran clean. I then dumped in 2 cans (as recommended) of a quality German cooling system cleaner (Liqui-Moly Radiator Cleaner), and let the engine to idle for 30 minutes as instructed. Basically, there was no coolant in the engine at this point, just pure water and the cleaner.

I then went through 80 liters of distilled water to flush out the system. I bought 8 10L plastic jerry cans, filled them up and that made things easier. This is basically 5 times the cooling system capacity (16L) to make sure the engine system is thoroughly flushed, leaving no traces of the old stuff behind.

nterestingly enough, the coolant after the flush did come out with an orange tint. Once that stopped, and I had clear distilled water coming out, I went ahead and adjusted the coolant to water ratio at 50/50 (2 gallons of coolant). I replaced the thermostat, reconnected the upper radiator hose and that was that.

It's been a while now, and the coolant is still the pale yellow it's supposed to be.