Dear BL: ENGINE RECENTLY STARTED TO OVERHEAT. I ADDED ABOUT
A LITRE OF WATER DIRECTLY INTO THE RADIATOR. I WAITED
APPROXIMATELY 20
MINUTES, THEN I TOOK THE CAR FOR A RIDE. THE TEMP GAUGE STAYED
WITHIN
NORMAL LIMITS, UNTIL I STOPPED. THE TEMP GAUGE CLIMBED INTO THE RED
ZONE
WHEN I LET IT IDLE. COULD THIS PROBLEM BE THE WATER PUMP OR
THERMOSTAT?
BY THE WAY, WHERE IS THE THERMOSTAT LOCATED ON THIS ENGINE? 3.1
LITRE  
ANY HELP WOULD BE GREATLY APPRECIATED. THANKS






BL:
It could be a t-stat sticking. These engines known for lower intake gaskets leaking
internally and externally. Also the rear headgasket for leaking externally, or allowing
combustion into the cooling system. Temp. gauge normal while driving, but
overheating at idle could also be cooling fans not running, or a restriction in the
cooling system- mainly the radiator.
The t-stat is inside the housing that the upper radiator hose is attached to. It is
under the exhaust crossover, held on with two 13mm bolts and is difficult to reach.
Removing the throttle body helps.

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Common areas of coolant leak on the 3.1L and 3.4L GM v6 engine.
1- thermostat inside housing. Pic with throttle body and exhaust crossover removed.
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