temp gauge problem

[brackie1]

my temp gauge is reading 240 degrees but the actual reading with a thermal gun is 190 degrees where the temp sensors located. I don't know if the gauge is bad or the sensors are bad. I there any way to determine whether either of them are good. Can either of them be tested with a meter?

Gene

[courtenay]

Not sure if the 78 will be the same as the 80, but on my 80, there are two sensors. Both located in the centre of the block. The one closest to the rad "pegs" the needle when the engine overheats. The one closest to the firewall feeds the temp to the needle. Disconnect the wire to the sensor closest to the block. If the needle returns to normal temp (around 190) then it's likely that the pegging sensor is pooched.

[micbrody]

My gauge suddenly read incorrectly high immediately after I was mucking around behind dashboard.

Turns out that the connector to meter from sender was not making a great connection (oxidation); and when I manipulated the dash, the connector slightly moved to a more oxidized part of connector.
The gauge works by measuring resistance to the sender.

I cleaned up contacts ; problem solved

[brackie1]

So I now have new temp sensors to install. However, the forward sensor which is for the over heat light will not come loose. I did not use my torque wrench. Should it be that difficult to remove?

[brackie1]

So, I finally got the water temperature gauge sending unit removed and replaced. After 6 months of flushing and refilling the cooling system several times, replacing radiator fan switch. The problem was actually the sending unit. A simple $10 fix. However, I learned a lot. I learned how to test the temperature gauge itself. Simply remove the wire from the sending unit and ground it. Turn on the ignition. If temperature gauge is working properly it will go to full hot immediately.

[RMaxfield]

Have you bled the cooling system? If there is air in the cooling system it will mess with the sensors. That makes the temp gauge go off the chart and once relieved goes back down. I just answered this really old post but hope it helps someone.

[brackie1]

Thanks for the reply. I have bled and burped this thing until I'm blue in the face. After installing new sending unit I drove it for an hour about 60 miles. Temp stayed at 190. Will keep am eye on it.

[Frog2Spider]

You may have already done this, but just in case.

Let it idle and see what the temp gauge reads when the fan comes on. Should be just about 200.

Cooling systems can be a challenge!

Dave.

[brackie1]

Your right about the challenge. I'll try it.

[brackie1]

Yea, temp gauge and rad fan match.

[maluminse]

Not sure if the 78 will be the same as the 80, but on my 80, there are two sensors. Both located in the centre of the block. The one closest to the rad "pegs" the needle when the engine overheats. The one closest to the firewall feeds the temp to the needle. Disconnect the wire to the sensor closest to the block. If the needle returns to normal temp (around 190) then it's likely that the pegging sensor is pooched.

Get out. So the overheat pegs it and doesnt turn on a light? Interesting. Mine is pegged. Car is cool.

So its the 'overheat' sensor which is faulty and not the temperature sensor which is faulty. No overheat light huh? Interesting.