1994 GMC pickup,5.7L 111,ooo miles - engine miss at oper. temp.

Oil in the coolant is usually an intake manifold gasket problem on these engines. If a head gasket failure the engine will normally overheat and give erratic temp guage readings. Make sure the oil level is full. Is the rattle noise coming from the engine? Some times the exhaust (converter) will fail and the catylist will seperate causing a rattle noise from the exhaust and plug it up giving a no power situation

Possibly a faulty spark plug or fuel injection problem. Have computer scanned & emissions checked.

Hi there,
My name is Steve. I can tell you that the barometric pressure sensor can, in no way, effect the temperature gauge operation. The gauge gets a signal from the engine computer which, in turn, gets a reading from the coolant temperature sensor. Your first step should be to have the check engine light diagnosed properly...starting with checking for codes. You likely have a code(s) relating to engine temperature or the temperature sensor circuit. Most common problems are erratic sensor operation and corrosion or oil contamination in the coolant temperature sensor connector. You will be time and money ahead by having a professional diagnose the problem correctly before deciding to buy any parts.

Yes,that is normal for these vehicles.I have one and bought new also,and that's the operating temperature on gauge,will make you think though,but look how high it goes.

YOU MAY HAVE A THERMSTAT IS THE STUCK PARTIALLY CLOSE
NOT ALLOWING FULL FLOW OF COOLANT THROUGHOUT ENGINE, TRY TO REPLACE THE THERMSTAT. WHAT ENGINE IS IT? 4.3L,5,7L ?

That would depend on the thermostat it has in it. Typically full operating temperature should be 195 degrees.

Any engine, when cold, takes at least 3 miles before reaching operating temperature.. After reaching operating temp it still takes a mile or 8(depending on your vehicle) before "over" temperatures are reached. Therefore if needed, a vehicle can be driven several miles without any coolant/water at all before overheating and causing damage, if started from from cold.

could be clogged cats or may even be bad crank sensor.

sounds like a bad map sencor

What temp is the vehicle running? For proper closed loop operation of the computer. The engine needs to run at least a certain temp . Check for proper thermostat operation...