On Saturday, April 18, 2015 at 2:34:30 PM UTC-4, Tony Hwang wrote:
trader_4 wrote:
On Saturday, April 18, 2015 at 8:39:46 AM UTC-4, wrote:
On Sat, 18 Apr 2015 04:39:42 -0700 (PDT), bob haller
wrote:

On Saturday, April 18, 2015 at 1:45:46 AM UTC-4, 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.

most head gasket leaks crate white exhaust.

if coolant leaks into oil engine will soon be siezed
First question - what year and model???

If it has a leaking headgasket, nothing else matters. It NEEDS to be
fixed (or thecar scrapped)

+1

I can't explain the behavior of why it runs hot at idle in
terms of the leaking headgasket. I'd suspect that there might
be another problem, like blocked radiator, that's the real
problem, even though OP says that has been ruled out. If there
is a separate cooling system problem, that could have allowed
the car to overheat, warp the head, and that's why the head
gasket is leaking. Symptom of partially blocked radiator
can be overheating at idle. With the car not moving, less air
moves through radiator, so it needs more radiator performance
that when it's moving.

Hi,
Today's new cars rad. fan is thermostat controlled electric motor
driven. So Air passing thru the rad. is not like old cars. If suspected
we can do the rad pressure test with dye which will tell what's going
on. If it is a leaking gasket problem the sooner the repair is done the
better. Or bigger problems will happen.

That's a good point. If it's a car made in the last couple of
decades, it probably has an electric radiator fan. If that isn't
running when the car needs it, ie when the temp is going up, that
would cause overheating. Even many older cars had auxiliary electric
fans to supplement the mechanical, belt drive one.