why does my engine temperature gage fluctuate wildly ranging from 1 full bar below mid range to 2 full bars above mid range in the middle of a 2 hour drive on the interstate?

Asked by migration_CYBERDALE Jun 24, 2014 at 05:41 PM about the 2003 Chevrolet Monte Carlo SS FWD

Question type: Maintenance & Repair

1. new radiator (1.5 yrs old) 2. out side air temp 85 degrees. 3 new water pump (1.3 yrs
old). 4 new thermostat (2 yrs old). 5 just replaced upper intake plenum (2 months old) 6.
new temp sending unit (3 yrs old). new belts and hoses. engine only has 21000 miles on
it.  I do not trust the accuracy of the gauge at this point.  Dealer told me that my gauges
tested fine (2 yrs ago).

1 Answer
51,265

John answered 10 years ago

Fan thermocouple sensor or relay going bad? Sounds like the fans cut out after the set running temperature then kick in when it gets hot. Have the fan thermocouple switch checked. Also check to see if your bug collection in the radiator needs changing. Anything that can block the air flow may cause this also. Is there a "secure" connection to the engine temperature sensor? When the engine goes two bars above normal, pull over and see if the fans are running. You also might have the coolant level checked. Low levels can also give that type of reading.

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