The temperature guage in the instrument panel reads low all the time on my 1986 Dodge D150 pickup with the six cylinder engine. It is on the second mark past "C" when the engine is running. I thought it should be in the middle of the guage range. I bought two different sending units from two different companies and both do not produce any reading at all! Both read stone cold. I suspect that they are really for a V8 engine. I cleaned the contact on the connector for the sending unit but it made no difference. Do I need to put something on the sending unit threads? Do you think the guage is bad or the instrumental panel voltage is incorrect? All the other instruments seem to work fine. Does anyone have any ideas?

Check the IVR (instrument voltage regulator. You'll need a VOM. Measure the voltage at the sending unit wire, without the sender connected. The meter should swing between zero and battery voltage, with the pulse width duty cycle ~40%. This produces an average of 5 volts. You can use a DMM that has frequency and duty cycle measurement modes to measure the duty cycle. Another way to measure the average voltage is to connect an electrolytic capacitor to the sender lead, and measure the voltage directly. + goes to the lead, - goes to ground; the capacitor should be rated 15 volts or higher, and the capacitance value is not critical, but larger is better. ~100 uF should be sufficient. An analog VOM is best for seeing the operation of the IVR.

The IVR is a rectangular metal can with 3 connector blades. Its plugged into the back of the instrument panel. You *may* be able to see/reach it if you do a headstand in the driver's footwell. If not, remove the 5 screws from the top of the bezel and 1 above the radio. Pull the bezel out of the dashboard. There are 6 clips on the bottom, so you may need to gently pry it. This exposed the instrument cluster. Remove the cluster screws and pull it out of the dashboard so you can reach behind and release the speedometer cable. Pull it further out to remove the two harness connectors. While the cluster is you, examine the light bulbs. If they have a shiny silver coating inside the envelope, replace them. The sockets have a locking tab that has to be lifted slightly before turning the socket, or they'll break off.

The IVR can be replaced with a mechanical one (either new or junkyard), or else install a solid state diy or aftermarket unit. I *think* Chrysler, GM and Ford all used the same IVR, so a junkyard search is easy. If you're comfortable with electronics, you can build one using a few Radio Shack parts. The parts count is so small that its not worth ordering from DigiKey or Mouser.

Ken

Your thermostat may be stuck open...............

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Ed's point is a good one. Do you have access to an infrared temp gauge to actually check the radiator temp, and thermostat housing temp?

Sam

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Has your temp gauge ever read anything other then what it reads? Stuck open thermostat is common, Air trapped in cooling system is also a possiblilty.. temp gun or some kind of temp gauge may be needed to read temprature.. YOu can remove the thermostat and boil test it to see what temp it is opening, Also due a visual on thermostat lock for deep scratches in thermostat shaft behind temp spring..

Warning! Resurrecting an old thread! (but hey, that's what search is for!)

I'm facing the same issue with my '73 Valiant. I've installed a boil-tested 195º Thermostat under the assumption that I was facing a stuck thermostat… And the problem persists. The temperature gauge does move, it just never moves above the 2nd line.

The heater does push out nice, warm air and the top hose does heat up, so I know the thermostat itself is working and there don't seem to be any clogging issues.

Could this be an issue with the temperature sender, a weak connection in its wire, or a problem with the gauge itself?

(The gas gauge also works and seems fairly accurate: had ~1/4 tank indicated, added 6 gallons, now have ~5/8 tank indicated)