Okay, I've searched and can find all kinds of stuff on the temp gauge sticking high, but nothing like what happened to me this morning. I was in 'slow and go' traffic because of an accident and, living in Florida, checked my 'Temp' gauge. It was somewhere near the "A", which is okay for a Zetec. Looked down sometime later and it was all the way over like the engine was cold soaked! As I picked up speed past the accident, it jumped up a little, and by the time I got to work (say 15 min) it was back where it should be.

Any thoughts? Bad sender? I read that there are two, one for the ECM and one for the Temp Gauge...

It could be a bad sending unit. Also it could be getting a bad connection so make sure you check them. Also the gauge itself might be bad but I dont think thats the case. Thats my 2 cents on the situation. Well I hope you find the problem.

damn...i wish my temp gauge would get stuck on LOW . lately it seems to be riding between the A and the L...hmmm

I would agree with 2KSE... While looking at some other electrical diagrams last night, It looked like the guage would show no reading if the circuit was open. (broken wire or loose connection)

My temp gauge is acting weird as well. It used to always be right in the middle, close to the "M" One day after driving on the freweway for 2.5 hours, i looked down and it was between the N and the O. Now it goes back and forth all the time. It used to always stay at the same spot.

Another thing to consider is that the thermostat may have failed in the open position. If the thermostat is permanently "open" the engine will be VERY slow to warm up and may not even get off the "cold" mark, especially in cold weather.

I replaced my temperature sending unit a few weeks ago. Yes, it's different than the coolant temperature sensor that goes to the computer. So it won't affect how your fans come on, etc. However, I do have a duratec, so your zetec may be a bit different. But I think the general principle is the same. It's a little hex-shaped thing.

At any rate, it was a super easy fix on my SVT. About 10 minutes.

One thing about your post concerns me, however. My gauge pegged way past the "L," and it stayed there until I fixed it. Your gauge staying at the cooler end may be indicating something other than just a bad unit (loose or cut wire, etc.).

Originally posted by zaphod_fl:

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It was somewhere near the "A", which is okay for a Zetec. Looked down sometime later and it was all the way over like the engine was cold soaked! As I picked up speed past the accident, it jumped up a little, and by the time I got to work (say 15 min) it was back where it should be.

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I had the same thing last year, from time to time it fell to
zero and gradually went back up.

To verify, when it is down, stop the car, (leave the engine
running), open hood & tap the thermostat housing and the
wires. For me it looked very much like a wire contact
problem (moving the wires always / tapping always solved it
momentarily) but at the end it turned out to be a sensor.
It was < $20 from autozone, and it was the one facing DOWNWARDS
from the thermostat house.
Both autozone & dealer kept saying that the gauge is driven
from the other sensor (facing upwards from the th. housing),
I changed it for no result, finally changed the
other one and it fixed the problem.

Tiv