How do you test temperature sending units?

[nrgflow]

I think I might be having issues with my temp and oil gauge but wanted to make sure if its either the sending unit or the guages malfunctioning. If I connect a meter between the plug on the sending unit and a ground while temp is zero, what ohm reading should I be receiving?

Thanks!

[71 fun]

Take the temp guage wire off the sender and touch it to ground, your temp guage should peg. hope this helps.

[nrgflow]

I found out that my guage is working by performing the test that you have mentioned. How do you verify that the sending unit is working correctly with a meter?

[TIMSPEED]

I need to know how to test that sensor too. My guage is working, because when I ground it out, it pegs out. So, it MUST be my sensor, right?

[DrMaserati]

Remove the temp probe/sender from the engine. With the gauge wire attached, suspend the probe in a pan of hot/boiling water along with an accurate thermometer. The thermometer and the gauge should read close to the same. Keep in mind that factory gauges are not known for great accuracy, so there will probably be some small difference.

While we are on the subject of testing, here's another tip. In the shop where I used to work, we NEVER installed a new thermostat without testing it first. Suspend the thermostat in a container of water along with a thermometer. Heat the water and you will be able to watch the thermostat open as the water temp rises and while you monitor the temp. Make sure the thermostat is suspended in the water and not in contact with the container.

JP

[71 fun]

Most part stores carry manual temp guages that come with an adaptor which you can thread into any water port in your block, or intake manifold, (1/2" npt.) for test purposes.

[Grim Reaper]

Originally posted by DrMaserati
Remove the temp probe/sender from the engine. With the gauge wire attached, suspend the probe in a pan of hot/boiling water along with an accurate thermometer. The thermometer and the gauge should read close to the same. Keep in mind that factory gauges are not known for great accuracy, so there will probably be some small difference.

While we are on the subject of testing, here's another tip. In the shop where I used to work, we NEVER installed a new thermostat without testing it first. Suspend the thermostat in a container of water along with a thermometer. Heat the water and you will be able to watch the thermostat open as the water temp rises and while you monitor the temp. Make sure the thermostat is suspended in the water and not in contact with the container.

JP

Uhhhhh The sender varies the conection to ground. If it's not touching anything you get no reading. The sender has to be gounded to the same power source that the gage is connected too. The exception would be a mechanical gage.

There are other things that can effect gage readings. Bad rectifier or regulator in your alternator can throw the gages off. Too low of voltage from a poor ground can also cause issues.

A classic mistake with these trucks when doing engine work that involved removing the engine or the heads is to forget to hook up the ground strap off the back of the passengerside head to the fire wall. Symtoms include gages bouncing when turn signals are on. Some lights work with the running lights off but don't work with them on.

Old wires and long wires have voltage drop. Check your voltage at the battery with the engine running and check the voltage in the truck at the cig plug. On my 88 low mile burb I loose a 1/4 volt between the two and I have run a second ground wire from the battery dirctly to the fire wall. Before I did that I was loosing 1/3 of a volt.

[DrMaserati]

Originally posted by Grim Reaper
Uhhhhh The sender varies the conection to ground. If it's not touching anything you get no reading. The sender has to be gounded to the same power source that the gage is connected too.

Uhhhhhh, You're absolutely correct. Sorry I neglected to mention that. Simply run a wire to ground while your doing the test.

JP