On Fri, 17 Apr 2015 22:50:00 -0700, "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.

A lot of cars run hot at low RPM. One guy had to shift into park at
red lights and "race the engine" to cool it down. Didn't overheat on
the highway. Probable clogged radiator or bad water pump. .