Quote:
Lean a/f mixture should cool the cylinder heads a little, not make the water temperature go up. But pinging alone can cause the piston to burn, then the gasket can get scorched, start leaking water and then an engine will massively overheat.

That's probably not the problem with your car Mareo, if it's not losing coolant on most trips where it gets warmer and warmer. If the coolant is leaking out somewhere ...

Bob makes a good point, detonation is bad if it continues for more than just a brief period. The newer engines run just on the edge of detonation (using the knock sensor) to get the best mileage and power (advanced timing). But you shouldn't hear it, the knock sensor is like a microphone and can hear it when it's just starting. Then the black box reduces the timing within a few thousandths of a second.

Heat will affect pinging (replacing a 180 or 195 degree thermostat with a 160 one will often stop pinging). Compression will do it most dramatically (regular gas likes 8.5-9.0 generally speaking). Timing will cause it.

Anything that causes hot spots in the combustion chamber can potentially cause or contribute to detonation:

- hot intake air
- stuck heat riser in exhaust manifold
- stuck heated-air flap in air cleaner
- Spark plugs with too high heat range
- overly warm engine
- deposits in the engine
- lean burn
- initial timing
- timing advance (vacuum)
- centrifical timing (weights in distributor)
- low octane fuel
- high compression

Lean a/f mixture shouldn't heat up the water temp. However, it'll cause burning later in the cycle and burn through the exhaust port, sometimes creating hot valves and piston tops. Deposits in the engine (carbon, etc) can get hot enough to detonate the fuel before the spark goes, causing the "ping" sound. Sometimes it can burn the valve or valve seat or piston top. If bad enough the hammering can break the piston.