My temperature gauge on the dash has been stuck on COLD for about a year. The heater produces hot air no problem. I changed the thermostat anyway, but it didn't make any difference. So when my mechanic was doing some other work on the engine, I asked him to change the temperature sending unit and check the wires for damage while he had the truck on the lift.. He changed the temp sending unit and he said the wires looked OK visibly. However the needle still is stuck on COLD no matter how long I drive it. The engine runs fine, and there is no evidence of overheating. I would just like to get the temp gauge to work, so I can monitor things better on this old truck.
I am wondering if there is any electrical connection in the steering column (clockspring or ignition switch) that could be broken, and cause the temp gauge needle to malfunction. The reason that I say this, is because there seems to be a lot of "up and down" play in the steering wheel.
Have you considered that the temp guage itself is toast?
You are looking at the complicated stuff like the steering wheel play -- or the wrong stuff in the case of the t-stat -- but ignoring the actual symptom.
There may be two temp sending units on the motor, one that feeds the guage and another that tells the computer what the engine temp is. Both of these could be handled by the same part, but there are many applications where the engineers use two different senders. You need figure out if the mechanic changed the right one IF you have two of them.
Then, the guage itself is usually pretty reliable, but they have been known to fail. If you have been poking around inside the dash installing (a radio for instance), you may have simply pulled one of the wires off the back of the guage.
If it is the same as my 1995 Bronco - should be exactly the same - it is very simple to pull the cluster. It should take your mechanic not more than 5 minutes to have it out. I don't remember whether the guages can be replaced individually or not, though.
On my 91 F150 4.9 there are two temperature units, one is a sensor up by the thermostat housing for the computer (the more expensive one) and a sender for the gauge down on the passenger side of the engine block (about $5 at O'Reilly's but of course the hardest one to get to). You will need to drain the coolant down or you will get a shower when you take the sender out. I put a coat of never seize on the threads of the new sender before screwing it back in. You can ground the wire to the sender and the gauge will rise to it's maximum when you turn the ignition key on. I used a jumper wire with an open spade connector on one end and slid it under the wire terminal that snaps on the sender. Just ease it up and slide the spade terminal on the sender stud and push the pickups wiring terminal back down tight. The sender stud is just like the old ones with a #10 threaded stud but the vehicle terminal just pushs on like the old ones did. It makes it a lot easier to ground it out with the jumper because the sender is up in an awkward place to get to. My gauge just barely moves now and stays on the very low end of the scale but it "does" move now. It will move up just a little more in the hot summer when the temperature gets up around 100.
"GWK" wrote in message news:VfCdnVg8l7KhzuzbnZ2dnUVZ snipped-for-privacy@ptd.net...
If the heater in your truck has working normally, that should tell you that the engine is warming into the normal operating range if not exactly accurate on the temperature gauge. If the temperature gauge is not rising at all I would hope that your mechanic tested the gauge before replacing the sensor by grounding the wire that attaches to the sending unit directly to the engine block to determine whether or not the gauge rises. With the wire completely grounded to the engine block, the temperature gauge should go well into the normal range if not all the way to the hot range. If the gauge does not rise, that is an indication that there is an electrical problem with the gauge or the electrical circuit. Check the voltage from the sender wire to ground. If I recall correctly, you should have approximately 5 volts at that point. However it is possible to have as much as system voltage at that point. I do not recall which it is on your particular application. The important thing is whether or not you have voltage. If you have the correct voltage at the sender, then a replacement sender should return to gauge to proper operation. If it does not, you likely have a defective gauge that will require replacement. The gauges on that vehicle are supplied in pairs, such that you have to buy another gauge in addition to the temperature gauge which other gauge is dependent upon your particular instrument panel configuration. If I recall correctly, it is not possible for the paired gauge to work properly, and the other not work properly if there is no voltage present on one or the other of the gauges. You can also test the temperature sending unit by checking it with an ohm meter. Do this by checking the sender for resistance before starting the engine when it is cold. Checked the resistance again when the engine is completely warmed. You should see a drastic reduction in the resistance reading. A good service manual will provide a resistance chart for various engine coolant temperatures.
I would hope that your mechanic was knowledgeable enough and conscientious enough about his work to have done these simple and quickly conducted test before replacing your temperature sender. I also hope that he is aware that your engine has two temperature sender's. One is the engine coolant temperature sensor for the ECM and the other is for the engine temperature gauge on the instrument panel. If he could not distinguish the two he may have replaced the wrong part with the wrong part.
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