Temperature Gauge Fluctuations

[wilnwil]

I have a question concerning my '96 Taurus...
Its probably going to sound dumb but when you don't know, its always good to ask right?
Ok, after my car is warmed up the temperature gauge gets to just below half on the temp scale then it drops down to 1/4, slowly raises back to 1/2 then drops over and over. Is this normal? Is it just the thermostat working or should the gauge be at a constant temperature?
We had a leaky coolant reservoir tank which we replaced a few weeks back so there are no leaks in the system.
Thanks for your time!

[joe92k1500]

Could be a bad thermostat, or some air in the system. I would lean toward a bad thermostat.

[wilnwil]

We put a new thermostat in a few weeks ago, if its air in the system, how do you get it out?

[TomV]

When did this symptom first occur? Was it soon after the thermo replacement?

I would venture a guess that if the thermo was of too high a temp then you might get wider fluctuations in the temp guage than you are used to.

Is there sufficient coolant in the sysytem?

[wilnwil]

its seems to have gotten more noticeable after the coolant reservoir tank was replaced so I'm thinking maybe the air in the system idea sounds good? The system wasn't purged of air after new coolant was added after the tank replacement.

[TomV]

Originally Posted by wilnwil

its seems to have gotten more noticeable after the coolant reservoir tank was replaced so I'm thinking maybe the air in the system idea sounds good? The system wasn't purged of air after new coolant was added after the tank replacement.

Is the fluid level in the tank rising when hot? Does it drop when cool? Is it within the indicator lines on the tank? If so, that would tell me that there is enough fluid in your system.

Based on what my Haynes manual is saying, you fill the tank with antifreeze and run the engine until the thermostat opens (upper radiator hose is hot). Stop the engine and let the engine cool. The fluid from the tank should be draw into the engine as the pressure is reduced.

If the fluid level goes below the Low line, add more fluid to reach the Low line.

Run the engine again until the fluid stays at or above the Low line when cool.

If there is air in the system then it should be forced out into the tank. There may some pressure in the tank because of this so take care when opening up the cap by using a rag over it.