Vortec engines aluminum? On 98' and 99' trucks, the block isn't,the heads aren't,the only part of the Vortec engines that is aluminum is the intake manifold. The green coolant is perfectly fine for all chevy engines. Texaco and GM went together to try and find a more environmentaly friendly coolant. They figured that if it lasts longer it's better for the enviroment.

You can mix the two types of coolant with no ill effects but you lose the long life of the Dex-Cool. The coolant then is to be treated like the standard green stuff.

I agree with the need to a complete flush if you do the switch. In one of the service bulletins I got from GM it goes into very detailed directions on how to do the flush.

If I owned a vehicle still under any warranty from GM I would stay with the Dex-cool of course.

My dad and brother have had Chevy trucks for a long time,the water pump in my brothers truck lasted until 189,000 miles.My dads work truck has over 150,000 miles on it, and his own truck has over 125,000 miles, both with the original water pumps and green coolant from the factory.

I'm convinced that with what I've read from GM and having to replace a water pump on a 98' and 99' Chev truck at just 50,000 miles ea, that the Dex-cool is the reason. I hope you all have great luck with it,but for me it's the green coolant from now on!