65fastlane

How do I test my original coolant temperature guage? Right now it is inoperative, either do to wiring or a bad guage. The sender is known to be good.

Soaring

Here is one way.
http://www.madelectrical.com/worksho...mp-gauge.shtml

65fastlane

Thanks. That is interesting and helpfull information, however, I am interested in testing the guage itself. The guage simply does not register; there is no needle movement. I need to determine if the wiring is bad and/or if the guage is just kaput. If I ground the sender wire the guage should spike, yes?

Sean W.

im not qustioning your knowledge, but for the needel to move you have to wait for the thermometer to open up, that occurs after about letting it idel for about 10- 15 minutes. if still nothing happens i would take the guage out and make sure all the electrical connections are good...

65fastlane

Here's the thing: Im installing a 302 and would like to have confidence in the operation of the temp. guage prior to bring the engine up to operating temperature; I want to avoid overheating and causing any damage, you see. I know that before I started the project the guage did not register any temperature, ever, and would like to know that it is a faulty guage before spending money on a new one.

Brandontyler65

it could also be a bad temp sender or a bad voltage reg too

bodyputtyless

If you believe the "sender is good" because you have installed a "new" sender I have news for you. If you went to an auto parts store and bought a sending unit for your year Mustang and engine, they most likely sold you one that appeared larger in size. Oh the threads fit the hole but it wasn't an exact replacement. You need to get the sending unit that was made for those years. You will either get "no reading" or a "topped out " reading with the over the counter sending unit. Been there, done that as the saying goes.

Brandontyler65

i know i got one for mine when i got a new intake just to do everything over and i turned the key and i was so hot according to my gauge so i just ended up returning it and cleaning it up real nice

THUMPIN455

All senders do is change voltage. Doesnt matter it ifs an O2 sensor, a temp sensor, or a TPS. They change the voltae to the computer or guage. Of course mechanical ones dont.

Find the voltage range of the guage or sender, then using a rheostat you can check the readin on the guage at a known voltage and compare it to what the sender parameters are.

If you wanna get all technical about it anyway..

Easier way is to do like the page Soaring linked to. It will tell you if the guage is reading and what temp everything is on the dial.

coda618

If you want to check the wiring, you need a milti meter on the ohm setting. Pull the guage harness between fire wall and sender. Insert one lead to one end the other to the other end. if the wire is not good, the meter will indicate something like "line" or "open." Haven't done it in a while, but basically if the wire is good it will read zero or low resistance. If you OIL sender and guage are working and you know that wire is good, just test that wire and see what the reading is (its part of the same wire harness and plug) the one for the temp should be the same reading. If that tests ok, the next step would be to test the harness from the fire wall to the guage. Identify the color of the wire comign from the temp sender, get access to the back of the guage and disconnect the same wire. Test the lead the same way as above. You will prob need another person and an alligator clip to extend the testing probes on your multi meter. This should at least tell you that the problem is or is not with the wiring.

Also, how do you know the temp sender is good. Just because it is new? I worked in auto parts for many years and it is no uncommon for a new item to be defective. I am not sure how to test the guage itself.
Good luck.