"Snuffy \"Hub Cap\" McKinney" wrote:
This is more of a Sherlock Holmes type mystery than a practical matter.

Neighbor has a leaking head gasket in his Buick bad enough so that the
engine runs rough all the time. Watch does with it is not my concern.

When driving it runs cool. When sitting idling the temp increases
rapidly. If he puts in neutral and revs the engine, he says it drops to
normal quickly. Radiator, fan clutch, thermostat, water pump all checked
out and working normally.

I'm wondering .... when the engine is turning slowly, if the the coolant
pressure drops, which could be letting more exhaust leak into the coolant
and raise the temp? Says when the temp goes high, he can smell
antifreeze, probably blowing out the overflow.

The exaust should do nothing. Might need radiator and system cleaned. ?

Greg