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I recently had my oil light come on in my 2004 Chevy Malibu. This resulted in a visit to a mechanic (after putting 3 QTS of oil in it) to see if there might be something more serious than a leak going on. (Confession... I don't watch the oil as closely as I should but do have it changed every 3-4 months. It was about due.)

While the mechanic didn't do a thorough examination because his shop was full, he took a moment to check it out on the ground. He didn't seem concerned by the oil leak but did see some grey metallic corrosion on the lower right side of the engine near the back. This seemed to greatly concern him. He said it was caused by the Dex cool coolant that's in the car having gone bad. He basically told me the head gasket was going to blow in July because of the heat and that we should get a new car.

Later that day I also had a friend who is also a mechanic look at the car and said its fine, that if it was his he wouldn't get rid of it. He admitted that he hadn't seen that kind of corrosion before however.

As far as how the car runs, there doesn't appear to be any issues that would signal that there was an engine problem without looking under the hood and seeing the leaks. The car drives smoothly and idles well. No strange sounds except a very light metallic tapping noise that seems to only happen when the oil gets low. The engine has been running at a normal temperature.

What causes grey corrosion on an engine? (You can pull it off the engine really easy and it falls apart in your hand as my friend found out.) Is the car beyond hope?

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I'm highly skeptical of the first mechanic. While Dex coolant is nasty stuff (if possible, I'd replace it with standard ethylene glycol antifreeze, but you should check with someone who knows GM vehicles first), I find the claim that it caused corrosion on the outside of the engine rather doubtful. The idea that the head gasket is going to blow because of the weather is also pretty ridiculous; the temperature inside the engine should be the same as it always is if your cooling system is working properly.

Anyway, can you post a photo of the grey corrosion? Maybe someone here will have an idea what it is.

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