Coolant temp sensor

[CutLaredo]

Hi, has anyone experienced a coolant temp gauge that pins when the key is turned on, has a new temp sensing unit, but fails to register temp on the dash? Any suggestions?

[old_man]

Unplug the sensor and see if it does the same thing. If it does, you have a broken wire or loose connection somewhere. Most likely it is the connector on the back of the gauge cluster.

[Eagle]

Other possibilities, all relating to the new sender.

(1) Be sure you got the correct sender for your vehicle. The sender for idiot lights is a simple ON/OFF switch, while the one for gauges is a variable resistor.

(2) Be sure you got the correct sender for your year. In 1991 Chrysler reversed the polarity of the gauges. What this means is if you take the sender for a 90 and put it in a 91, it'll start off reading very hot, and then the reading will go down as the vehicle warms up.

[CutLaredo]

Thanks tom, I'm hoping thats not what it is, I have another question. With the key on shouldn't there be voltage registering at the terminal - to + in the engine compartment?

[CutLaredo]

Also the ohms at the positive teminal to the sensor housing were 10.29, and at the negative to the housing read 0.00. With the - battery terminal disconnected.

[old_man]

The easy way to check the wiring is to have the wire on the sensor disconnected and see which way the gage reads. Then short the wire to ground and it should read the other way. If the needle doesn't move, it's wiring, If it does move, its the sensor, either bad or wrong one.

Now comes the real question that I forgot to ask. What sensor are you changing? The one that runs the gage on the early engines is mounted on the drivers side rear of the head. The other one runs the computer.

http://www.a-v-t.com/XJTempSender.jpg
And the answer is NO I can't spell.

Another common problem is using teflon tape on the threads and ending up isolating the sensor from the block.