Probably best to put this in the engine section of the forum...
What you'll find is that a hot engine may be running leaner. A lean engine is ok in small bursts but in the long term you'll end up with a dead engine. Running lean makes the engine run hotter and thus your piston head is hotter and ends up fatiguing that can result in a hole in the piston or piston slap - common on EJ20 turbos in a particular cylinder due to the fuel delivery system's line up of the injectors.
What a lot of people don't realise is that the engine uses the fuel as a cooling method - by not burning all of it in the cylinder. The majority of the burn occurs in the cylinder, but there's a little bit of un-burnt fuel that's pushed into the exhaust where it's finished off. Ever taken the exhaust manifold off and revved an engine - you'll get these little blue flames dancing out the exhaust ports and dead hearing if you're not wearing ear muffs.
By leaning out the fuel you'll burn all of the mixture in the cylinder instead of some in the exhaust, this will result in a hotter operation temperature.
There was a case a number of years ago where a charter airline company had a plane go down and it was found that the bean counters had put the hard word on the pilots to run the engines leaner to save on fuel. This lead to maintenance issues and some plane's engine's failing mid-flight due to holes in the pistons. One went down killing all on board for the sake of a few dollars here and there. Not worth the pain!
Yes better fuel economy is good, but you want to make sure it's because you're doing it properly
Cheers
Bennie
