I have encountered a troublesome problem on my 1971 Cutlass. After the motor gets hot from idling, it gets so hot that the rubber motor mounts are actually melting! I had the engine rebuilt recently and I have yet to be able to safely drive the car due to this condition. The engine has some mild performance work done to it, and it has headers which i wrapped with heat-insulated header wrap. The engine is not overheating, it's just radiating a great deal of heat from the block/headers. Does anybody know what would be causing this?

 

That's a new one on me. It should take a whole lot more heat to melt the rubber in your mounts. Something is definitely wrong there.
As to what that is I couldn't tell you.

 

Low coolant..Fan is not coming on. Thermostat not opening or is stuck partially open. Clog in the system somewhere.

 

Check again. This is a 1971 he's got and there is no electric fan not to come on. And even so if the engine were to over heat the mounts still should not get hot enough to melt. Not by a LONG shot.

 

The only thing I can come up with is a bad engine ground, and the power is trying to find ground through the mounts. I agree with svnt, there's NO WAY overheating is melting mounts, there'd be alot more issues before the mounts would melt. Keep us posted, I'm curious.