Temp. guage problem C2

[James B.]

Temp. guage will not read above 140 degrees, new sending unit and new guage, doing same thing with old unit and gauge...any ideas?
Kayo.80@netzero.com

[Stephen L.]

Re: Temp. guage problem C2

As the temp goes up the resistance of the sender goes down. Sounds like you may have some corrosion in a wiring connector causing an increase in total system resistance...it doesn't take much.

[Randy S.]

Re: Temp. guage problem C2

Jim,

Lots of info in archives, I battled this problem too.

Do NOT use teflon tape at sender connection, good groumd required

A high resiance ground connection will display cooler than actual temperatures.

I ended up using a Lectric Limited sender to solve my problem. Lectric limited catalog has a good troubleshooting guide on temp gauge

Randy

[Edward Boyd]

Re: Temp. guage problem C2

Are you certain that your coolant is going above 140? Verify temperature with an IR sensor before driving yourself crazy looking for an electrical problem that may not exist.

[Les Jacobs]

Re: Temp. guage problem C2

You can do a quick check to determine whether the problem is with the sender or "everything else". Disconnect the electrical connection at the sender and jumper the connector end thru a 10 ohm, 2 watt resistor (from Radio shack) to ground. This simulates a "hot" sender. Turn the key "on". If the gauge reads "hot", the problem is not in the wiring, gauge etc, but rather in the sender or mounting thereof. If it reads cold, the sender is not the problem, and you need to dig into the wiring, connections, gauge etc as stated above. (I actually jumpered the connector directly to ground w/o the resistor without a problem, but I wasn't sure what the risk was. It was fine, but I don't know that it was safe or if I was just lucky)

[Jack H.]

Re: Temp. guage problem C2

Ten ohms is TOTALLY outside the defined temp vs. resistance profile of the original sender!!! The upper asymptote plateaus to 40 ohms and there you should be above 260F on the dial.

Using a hit/miss value that causes the temp gauge to PEG is not wise.... If you want to do this 'test' (nothing wrong with the basic approach mentioned except for the choice of resistance value), then use a resistor that makes sense and keeps the system within its original design tolerance window.

Use a 47 ohm resistor and the gauge's needle should smartly align to 240F if it's within calibration. PLUS, do this with the engine running/battery at typical driving level (approx 14 VDC) or you'll fool yourself with the results.

For a SHORT test (momentarily connect and while a helper peaks at the gauge), you can get by with a 1/2-watt resistor. For any appreciable duration, the 2W value suggested has a healthy power dissipation safety margin.