Had the coolant flushed today and the thermostat replaced. I never thought I'd like to see the color green so much. They used Prestone. There was alot of mud in the system. It was definitely remnants of the DEX-COOL. There was no oil or ATF in the coolant. The guy did a good job. He got as much of the mud and the old coolant out as he could. The coolant is still it's natural neon green. Nothing like before when the internals of the radiator and the overflow bottle were covered in brown specks of mud. The guy just said to check the freezing protection before next winter, but it should be good to at least -30F. Hard to believe that I just had the coolant changed less than a year ago at Valvoline and they would only use DEX-COOL and this happened. Good thing I don't go there anymore.

EDIT: Flushing the coolant also seem to have solved the new problem of temperature fluctuations between 190 and 220. Now it doesn't even go above 200-210. I am going to try some Royal Purple Purple Ice since I am gradually switching to Royal Purple products in this truck as they need to be changed.

 

Good luck with it. If you would read through the whole Dexcool thread, you would understand what happened rather than follow the flock on the matter.

 

I agree, sometimes with the aluminum parts on all the cars and trucks these days they react with the coolant and you can get these ugly mud looking stuff.....this info straight from a GM mechanic of over 30 years. You can flush the system but it may not completely get rid of it. Coolant is most likely...like 95% of the time...to leak into the oil not the other way around.

Good luck