why does the temperature gauge show an overheating engine.

Asked by Oct 19, 2013 at 09:44 AM about the 1998 Chevrolet Monte Carlo 2 Dr LS Coupe

Question type: Maintenance & Repair

1998 monte carlo 3.1 L I have changed the temp sensor, water pump , thermostat &
radiator. Pressurized the coolant system and found no leaks. I have cabin heat. The
radiator fans run continuously as long as the engine is on. I purchased a supplemental
temp gauge and installed it by removing the block coolant drain plug and  installing the
sensor. Now I can see both gauges operate simultaneously.  The supplemental gauge
indicated that the engine is operating well within range whereas the factory gauge still
shows overheating. The service engine light stays on and the car won't pass inspection
.  Other codes have popped up : PO1001 MAF sensor circuit range/performance
problem & low input.  PO118 engine coolant temp circuit high input. PO171 system too
lean.  PO305 cylinder #5 misfire detected (I replaced injector now ok). The temp sensor
has three wires Yellow =PCM,  Black = ground, DARK GREEN = temp gauge. On the
plug (unplugged & cold engine) I get 6.85 vdc between yel & dk grn.  5.80 ohms
between blk & dk grn. The  NEW sensor tests out at 3050 ohms at 70 (F) . I am
thinking the dash gauge could be the problem. Has anyone had this problem?

1 Answer

77,935

I work at NAPA and we have problems with some of the aftermarket temperature sensors for GMs. Try an AC Delco sensor. That usually solves the problem. HTH. -Jim

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