Temperature gauge is pegged when car warms up.

[ssvveenn]

One day out of the blue, my temperature gauge pegged on high. The car wasn't overheating, so I continued to drive home. I changed the sender with another used one and the symptoms are still present. When I first start the car cold, the gauge is down low. Then, when it warms up, it jumps to high. Any ideas?

[Petros]

Welcome to the list!

how do you know the car is not over heating? Have you put an auxiliary temp gauge in to make sure? It is worth knowing for sure. If your sender is good (did you replace the correct one? it is the one on the front of the head, not on the water outlet housing-that one is for the emissions control system), than the only other thing that can cause that is perhaps a chaffing wire that grounds out the sender wire. that is not that unusual of a problem on older cars. Possible gauge is bad too, but i have never seen a gauge go bad, more common to be sender or grounding wire. You also might take out the thermostat and test it, or just replace it if it is more than 2 years old. never trust an old t-stat.

where do you live?

Good luck.

[marlinh]

Is the coolant level up? Fan belt tight and not slipping on the water pump? Do you have full heat in the car, indication that you do not have an air lock in the system? A hand held temp gun is indispensable. Maybe you can stop by a shop and see what the temperature actually is when it is running. Do you hear a gurgling in the overflow bottle after the car is shut off and the gauge appears high?

[ssvveenn]

Well, I replaced the thermostat and checked the wire for grounding. The symptoms are still occurring. When I start it cold, the gauge is on cold, then in about 2 or 3 minutes, it slowly moves up until in the hot range. Also, I started the car after letting is sit for awhile and the gauge showed mid-range for about a minute and then climbed quickly to the red. It seems to me that this is indicating that the gauge is working. Also, my fuel gauge is working fine, so I don't think it's the instrument voltage regulator. I also confirmed that the sending unit is the correct one. The symptoms occur with both (used) sending units.

I did notice a little moisture at the base of the SVST? unit. (The unit that all the vacuum hoses plug into at the top/front of the engine, on the upper radiator hose housing). Might this unit be causing a problem?

By the way.....Thanks for the comments. I live on a quiet, lonely island and it's nice to know that there are other folks who love there Tercels.

[Petros]

I would get an auxilary temp gauge from an auto parts store and verify that the temp gauge is reading accurately. I presume your coolant level is up, and you are not losing coolant. What you decrib is what happens when the head gasket is leaking coolant into the cylinders, but you would also have large billows of white smoke (steam actually), and you would have to top up the coolant every time. So if it is not actually overheating, than clearly it has to be a faulty gauge, faulty sender, or bad wiring to the gauge.