I had an early 90's Camero come in for an over heating problem, the car was very high mileage, over 300 000km, and this car was from when Dex-Cool first came out. First thing I do is check the resivor, that is empty. I then pull the radiator cap to check the coolant level, only to find that it was sealed with a thick paste. I take a screwdriver and try to shove it threw the paste to see how deep it was or if it was just on the top. After i couldn't get the screwdriver down any further then 2 or 3 inches, i tried to pull the upper radiator hose off the thermostat housing, and I couldn't get it off because of the paste in the hose. After I got the go ahead to cut the hose off, I found that the paste was filling the entire cooling system. Turned out, that right when the car was new, it had a small coolant leak at the thermostat housing, and her "mechanic" husband did the fix. After the he finished with the leak, he filled it up with the regular green coolant, and added a stop leak to it. Needless to say, Dex-Cool and Green coolant have different chemical compositions and that the combination of the two, along with the glavanic reaction of the different metals in the cooling system, the cooling system started rotting away. All the way to the point where part of the cooling system had become clogged the contaminants that kept on forming in the coolant from the chemical reactions, kept on building up, to the point where it became a solid mass. She said that the car had just stared overheating, even though you could tell that it had been overhead many times before. There were major oil leaks from where the block, intake manifold and the heads had warped from the extreme heat, even the transmission bell housing was warped from the heat transfer. The warpage wasn't something that you had to measure to see, this was the point where you could see the bends. I'm amazed that the car still ran under its own powwer, let alone have the car had last that long on the original engine, with the original "long life" coolant, mixed with the wrong coolant. It was quite amazing.