How does running lean make an engine's pistons melt and such? Is it because there isn't enough gas to keep the cyl. cool?

 

Here's how I understand it. Lean causes temps. to rise due to a different mixture; ie air rich. Temps. go up and the cylinder starts to experience detonation to some extent. Detonation, or pre-ignition can burn a hole in the piston. As the temps. rise, the very thin sheen of oil on the piston skirt is easily burned off. Now there is no longer any protective barrier for the piston or between the ring and cylinder wall. Seizure or melting isn't far off.

 

that's pretty good... I never really understood the seriousness of being lean until i started modding. it can ruin an entire engine.

 

Simply put, a lean mixture burns hotter than a richer. A rich mixture has too much fuel for the air it is mixed with, so only part of the fuel burns before the air is exhausted. So you get less power, and a lot of wasted fuel. A lean mixture has too much air for the fuel, so it burns much more completely (more power) but also produces a lot more heat. It's not so much that the cooling system can't keep up, but that the oil on the cylinder walls burns off. Once that happens, combustion chamber temperatures rise quickly, eventually to the point that the rings/cylinder edges begin to melt. It's the fastest way to get a $4000 paperweight.