[RedDevil]

Originally Posted by stovie

I just know that having to richen a engine to drop temperature and leaning it out raises temperature sounds completely backwards to me and the excuses I hear about why that is make absolutely no sense at all.

At the danger of sounding like another excuse, I'll try explain the way I see it:

When you increase the amount of fuel for the same amount of air, you do increase the total volume of the exhaust gas (as the fuel will vaporize, whether completely burnt or not).
In a rich mixture you get more volume but as all the oxygen is used up, you won't produce more heat than is possible for that amount of oxygen.

In a perfect mixture most of the fuel gets burned and most of the oxygen is used up - but not all. The heat production is nearly the same as with the rich mixture, but as that heat is concentrated on a lesser volume of exhaust gas that gets hotter.

in a slightly lean mixture pretty much all the fuel gets burned, so the (even smaller volume of) exhaust gas gets as hot as it can be.

In an overly lean mixture the amount of heat produced drops faster than the total exhaust volume, I'd expect the temperature to finally drop again then.