Wavering Temperature Guage

Last night I put the thermostat w/o ball check valve into the '94 Taurus (see my two earlier posts). Both Autozone and Advanced Auto Parts offered 190-deg as “OEM temperature” and 160-deg. I used 190, but the new 'stat does not have a ball check valve.

Temperature guage is maybe a little higher on idle than before the change, but drops noticeably when moving along and varies while driving (e.g, cools down on a long downhill). I hear the fan going on and off at idle.

I do not recall the wavering temperature from before changing the t-stat, but I seldom use this car. Is the wavering temperature indicating a problem?

I’m thinking there is air in the cooling system that needs to be purged.
Do you have a purge valve (bleeder) on or near the thermostat housing?
Did you follow recommendations for filling the cooling system?

Haynes does not mention a purge valve for the 6-cyl. Maybe my fill procedure was not up to snuff (it was late out, and I did not see the Haynes reference to the other Chapter). I’ll get my hands on the car and try again.

Is it OK to run it as long as the guage does not indicate overheating, or am I getting bogus readings?

If the coolant sensor is reading in “air” instead of coolant, I believe you could be getting bogus readings. Also, an airlock condition is created. A car, for instance that is very low on coolant can give a “cold” reading on a temperature guage while overheating.

Click this link and check it out: (wavering guage and refilling)


I see from the Wrong Thermostat ? post that you were advised about the thermostat. I’d be darn sure I was putting in the correct one, correctly, or all this other stuff is meaningless.

It 's a 94 Taurus. Nobody should worry too much about one of those. Your coolant temperature will always be going up and down. Drive uphill and the temperature will go up, downhill, it goes down. The fan always goes on and off at idle because the temperature would go to overheating without a working fan. A good job has many faces, you just don’t recognize them all.

This discussion has moved to:

Thermostat, one more time