Fluctuating Coolant Temp. Gauge on 2000 Contour

The needle on the coolant temp. gauge will suddenly swing all the way to "hot" when I start the car. It will stay there for a couple of minutes, then will slowly fall back down into the "normal" temp. range. It will run in the normal range for awhile, but will eventually creep up into the "hot" zone again.
It has been doing this since Sunday 5/20/07.

There is coolant in the system. There are no signs of coolant leaking that I can tell. I had the thermostat replaced approximately 2 1/2 years ago.

Could try replacing the coolant sensor. ~$20 if I remember correctly...

hairhorn said:

...I had the thermostat replaced approximately 2 1/2 years ago.

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Why did you change the Thermostat at that time?

Temperature Gauge sender part numbers/waterpump

Temperature Gauge sender part numbers/waterpump

Check if cooling fan comes on with A/C or at "M" on temp gauge. Try a new Motorcraft gauge sender, If it hits hot from cold engine start. Or wiggle the sender connector, if it wobbles, it's bad. There are two types available from rockauto.com, teamfordparts.com or local dealer: Motorcraft SW5046 Ford F5RZ-10884-B, which I used in my 1998 Mystique Duratec, 1 wire connection. Motorcraft SW5030 Ford F5RZ-10884-A, has a 2 pin plug on it, which was the wrong one for my car, fits newer than 1998 (IIRC.) OR You might need a new waterpump although the 2000 model year should have the "good" white impeller pump, instead of the dubious black impeller pump. Sender located below the red word "coolant." I used a metal impeller pump made by Delco, and I beleve Autozone has one like it.

Tony2005,

I had the thermostat replaced a couple of years ago because the car kept overheating.

I just got the car back from the dealership today. They said that the coolant sensor was okay as was the water pump. Their verdict was that it was the thermostat again.

How's the temperature now? Thermostats can stick closed or bind up as they open.

I don't think a thermostat has anything to due with your gauge going to hot upon a cold startup. Definitely sensor/sender related.

hairhorn said:

Tony2005,

I had the thermostat replaced a couple of years ago because the car kept overheating.

I just got the car back from the dealership today. They said that the coolant sensor was okay as was the water pump. Their verdict was that it was the thermostat again.

Click to expand...

You need to replace the coolant temperature gauge sender. This is the bronze looking thing below the "co" in the word coolant on the picture.

Edit. For the 1996, Autozone has it as Wells TU205 for the Temperature Gauge Sender (Switch). Have them check if this is the correct one.

Fluctuating coolant temps are indicative of a blown or leaking head gasket. Been there, done that, although the symptoms you describe are slightly different.

coolant temperature gauge

coolant temperature gauge

I had a problem with the gauge stuck beyond the hot zone. so I replaced the temperature sending unit $18 at autozone. and the gauge works fine now.

I know in some other cars there is a voltage regulator (used to be a small IC with three pins mounted on a heatsink) in the instrument cluster for the guages such as the temperature guage. If that is erratic it could cause what you see and not be related to the sender. Don't know if that is the case with your car.

Mike

To be clear, the the coolant temperature sensor, also called engine coolant temperature sensor, or ECT, is responsible for flipping your fans on at a preset temperature to cool the engine. The sensor has nothing to do with the gauge, and looks like a brass crayon:


The temeperature sender is repsonsible for the gauge only. It translates heat into a voltage reading, sending the gauge one way or the other. It looks like this:

The sender "switch" see my previous post, can short out, which will peg the gauge. Unplug it until you get the new one, so the gauge won't get stuck. Been there. Usually the gauge sender fails from overheating, although it might have just got bumped or something.