Join Date: Apr 2006
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Those IR thermoms have gotten popular this year for just such jobs. Basically, the engine should be running at 140F for a raw water cooled engine, and 170-190F for a closed heat exchanger.
You should be able to take readings on the thermostat housing, the water pump, most sections of the block including those where the cooling hoses are attached, and while there will be quite a bit of variation, very little of the block--if any--should ever run much higher than the thermostat temperature.
The spot of the block where the engine temp sensor is screwed in, should register within 5 degrees of the thermostat rating, unless something is making the engine overheat. (Betting there is a problem.)