I did search already but I found the results inconclusive for my problem.

My coolant temp gauge was always off but worked. Since I knew for how much it was off it was OK for me. However, since a few days ago the gauge stays pegged to the left. When I turn the ignition key, the needle trembles and moves, but then goes back all the way to the left. It doesn't move at all when the engine warms up.

I looked at the temp gauge sending unit and connector and the connector is in pretty bad shape (brittle and cracked). The electrical connection itself seems OK, though.

My next step would be to get a new temp gauge sending unit and connector from the FS and see what happens. Any other suggestions before I do that as the parts alone are almost $60? Is it more likely that the gauge itself is bad? Or anything else?

BTW, I recently replaced the fan switch and now the fan comes on as it should again.

You can test the sender with an Ohm meter, range is from 1400Ω at 100ºF to 55Ω at 260º

I have seen the needles on the gauge become loose. This might be your problem. It is worth checking out after you have verified the sending unit and connection is okay. The needle just sticks on a little pin in the gauge. You can try to recrimp the needle but I don't think that is possible. I had success with just a little dab of glue. To make sure you have the needle positioned right, set it so it just barely touches the bottom of the thermometer in the gauge picture.

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Also for a quick check of the gauge and wiring you can ground the sender connector and the gauge should peg to the right. If not then there is something in the wiring not making contact or a bad gauge.

the connection on the cluster for the gauge is pin 11 on the 12 pin connector on the left side of the cluster.

Hopefully not hijacking this thread here, but I too have a non-working temp gauge. The sender reads the correct resistance for relative engine temp, and grounding the warning light wire turns on the idiot light. The connector is cracked, but like Yellowstone, it makes a good connection anyway. When the car is off, the gauge rests left of the 100 degree line, but moves to exactly the 100 degree mark when the key is turned on. I'm thinking bad gauge, but wondered if anyone has any better advice for me. Potentially (un)related info: this same car had messed up wiring in the column, and a non-working speedometer when I got it.

MMC try repositioning the needle like I mentioned. Do your gauge needles swing all the way over when you start the car?

No, it stays put only at 100 degrees, and never moves any farther no matter the temp of the car, or when starting. I'm thinking it's just got a bad gauge.

Ohm out the sender before you replace it, but I would bet it's the sender. Hopefully yours will come back to life....

Now, if you don't mind me hijacking your thread too! I had a similar problem, gage would set at 100 when engine was cold, and move to about 110 after the engine was fully warmed up. I replaced the sender, and now I sit at 100 when cold and as the engine warms up it pegs out to maximum temperature. I ohm'd out the sender and it is working correctly, anybody know is there a way to calibrate the gage itself?

If the resistance was too low, you could add a resistor somewhere in line before the gauge to calibrate it I suppose... but if it's too high, I'm not entirely sure what you would do to solve that.

I pulled the connector off the temp sending unit and when I ground the green/white cable the gauge needle pegs to the right (full); when I ground the green cable the "coolant warning light" in the cluster comes on.

I just received a multimeter I bought on eBay ($2.99, thank you, China!) and I will test the resistance of the temp sending unit now...

The other pin wont make contact to ground untill your over temp, it is just for the Temp. light.

It seems like your sender is working correctly. And if your gauge pegged when you grounded it, the wiring and the gauge seem to be working. The only thing it should be at this point is the connection to the sender. I am trying to find a chart that said what resistance the gauge should be at, at given temps.

Based on that table, my sender is not working correctly. I got 67 Ohms at 210 F - that's way off!

So, is my best bet getting a new temp gauge sending unit and connector?

quote Originally posted by yellowstone: Based on that table, my sender is not working correctly. I got 67 Ohms at 210 F - that's way off! So, is my best bet getting a new temp gauge sending unit and connector?

I would say yes ! It seems your sender is reading out of it normal range, but it should have your gauge pegged most the time it looks like.

But it doesn't. The needle is pegged at zero and doesn't move (see above)...

has anyone ever tried just cleaning the sensor itself (the part that makes contact with the coolant) with a scotch-brite and seeing if it works like it should again? I plan on doing this myself but haven't gotten around to it yet.

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quote Originally posted by yellowstone: But it doesn't. The needle is pegged at zero and doesn't move (see above)...

I think you may have had 2 issues. The sender seems to be bad, but I think you had a bad connection also. If the sender shows only 65Ω resistance to ground, then the gauge should go to 270 if it pegged when you grounded it with 0Ω resistance to ground. You said it was always wrong before, a bad connection probably caused more resistance before it finally went totally bad. Have you reconnected it since you started testing, and is it still at "0" ?

Cleaning the outside of the sensor wont help, it is an internal variable resistor that goes bad.