SAT Question Everyone Got Wrong

[teenix]

This next is definitely off topic, and this thread I suppose, but the thread title popped a memory in my head :-)

When I was a flight instructor, I used to pose a question to students (and some aircraft mechanics) related to the operation of the piston engine they were flying with.

These engines are fitted with a manually controlled fuel mixture lever which is used to lean the fuel/air ratio depending on the altitude you are flying at. The higher you go, the less air pressure available, so the engine will start to run rich unless you compensate.

Leaning a fuel mixture also increases the burn temperature, but only up to a peak, then the temperature starts dropping again - less fuel = less burn. Usually, but not always, an engine is set to run just before the peak temperature occurs. You use the exhaust gas temperature gauge to set this.

The problem that students get taught is that if you run an engine on the lean side of the peak, engine damage can occur because aluminum parts like pistons and perhaps valves and or their seats can burn and may lead to horrible consequences.

So I posed the question.

If you have the fuel mixture leaned to the hottest temperature possible, and continue to lean it while the engine and exhaust temperatures both begin reducing until the engine finally stalls, why does it cause an overheating problem? Those in the know should come up with the answer, but no-one I asked ever did.

PS
You got to love the English language, at school you are taught I before E except after C, so why is "thier" spelt wrong?

cheers

Tony