[largo77]

I decided to give the engine a quick wash over. After that I have noticed that the temp gauge started to fluctuate. I believe the wash started it, but I am not 100 % sure.

I have since driven about 700 miles, and the temp gauge can stay normal for hours before falling down over half way to the bottom. It then comes back and it can fluctuate like that for 10 to 20 minutes before returning to normal.

As far as I can understand, the engine runs fine while this is going on.

Can this be anything other than the termostat? Bad wire? better radiator cooling effect after cleaning? And should I get it fixed? It can stay fine for several hours; in yesterdays 14 hour drive it only happened twice.

Thanks

 

[Slaab4life]

Sounds like a thermostat to me, but I can't image its because of washing the engine (since the thermostat is internal). I think its worth changing the thermostat, its pretty cheap and not too hard to change out. Perhaps you bumped the connection for the temperature sensor? I would definitely look into that too.

 

[PMI]

Can this be anything other than the termostat? Bad wire? better radiator cooling effect after cleaning?

Other than the thermostat, there could be something wrong with the temp gauge sensor, or the wires from the sensor to the connector, or the connector itself. The connector is on a bracket with two others on the driver side of the engine block, just above the thermostat housing. An intermittent connection would do it. You could unplug the connector carefully, and try to clean the contacts. The gauge and the sensor can be tested separately. The thermostat has to be removed and replaced if not working right.

 

[earthworm]

A thermostat malfunction will be nearly consistent - caused by age and excessive heat. All of mine seem to be good for 7 to 10 years, then the car either over or under heats, and is slow to warm up..

The electric connections seem to be of a higher quality than before, but once loose/corroded, a state of erratic operation occurs..
It could well be a malignant temperature transmitter..
Its in the Haynes manual - the specs.