hey guys, my buddy owns a 94 teggy LS. His temp gauge reads that it is overheating while cruising (primarily in warmer weather) and surges occasionally in park and neutral, any ideas as to what this might be?

 

How do you know if its overheating physically or not? If a thermostat is stuck closed, coolant would cycle only through the engine and you would never find out except for the sensor.
It could be a number of reasons, but you guys better find out soon before you damage the engine.

 

If it is reading hot when the car is at a stop, it could be a bad thermostat. When the gauge starts to read hot, check to see if there is a big difference in temp between the upper and lower radiator hoses. If so, this usually indicates a bad t-stat but also possibly but less likely, a clogged radiator. If under the hot gauge reading you find that one hose is so hot that you can't hold it but you can easily hold the other hose, you will likely need a new t-stat.

If this is not the case, the problem could be a slightly blown head gasket where high temp combustion is getting into the coolant, but that is also not very likely unless your friend drove his car for a long while as it was overheating.

GL

 

Same question, how do you know the engine is not overheating, how did you check?

Most common cause of a "fluctuating" temperature gauge is air in the cooling system, bleed the system to make sure there is no air in it.

If air is not the problem test the "Engine Coolant Temperature Gauge Sending Unit", make sure the plug is connected properly.

If the above is good then the problem could be the gauge itself, the ECU/ECM or wiring.
Do you get a code? 94