Coolant gauge reading 1/4 high?

[Ryan Stewart]

Ok, here is the situation. ONLY with the engine running and only sometimes, after the engine has been running for a while does the gauge read high. If you shut the engine off and turn it back on instantly the gauge moves back to half and stays that way for a while. Eventually it MAY go back up but doesnt always. The needle also moves whenever I use the interior fan, flip on the lights, or any other electrical device that takes more than negligable power.

I checked the sensor, its at 48.x ohms with the engine is up to temp. The M50 sensor, however, is ALWAYS getting 4.93 volts supplied to it while the M20 sensor gets 7.2 volts when the ignition is on but the car ISNT running and 8.3 volts when the engine is running (and its reading a hair high but not a quarter).

The way the wiring is the M20 sensor goes directly to the body wiring harness plug for its power and then the engine is the ground. I have basically ruled out the engine wiring harness being any type of a culprit. Now i just need to figure out if the 8v is more than the system should be seeing and that is why its reading high or another reason, and why it is supplying too much voltage if that IS the case?

Any ideas? Can anyone pull the plug to their temp sensor and see what kinda voltage its being supplied?

[ringmeister81]

Sorry to bump a really old thread, but I've been having the same problem. Exactly. Temp needle moves (up) when I switch on the fan, use blinkers, hit brakes, turn on lights. During the daytime, with no other electronics turned on it stays pretty consistent. But sometimes the temp needle goes crazy and bounces all over the place (after warm up). Changed the temp sender, but that didn't fix the issue. I've been searching the forums and can't find a fix.. Any ideas?

[jperris]

I suspect the problem is in the cluster. Possibly a poor connection causing high resistance on the ground leg of the temp gauge between the gauge and the si board.

[ringmeister81]

I think it could possibly be the ground nut on the back of the gauge.. I will check that tomorrow for sure.. But last night I was driving home from my girlfriends, which is only 10 minutes away, and the needle started acting all crazy again... And then, sudden loss of power and car felt like it was gonna die... I pulled over immediately, and let it idle for a minute. The idle was very rough, sounded like it was missing and about to stall. The temp needle was creeping to the red and then bouncing all over the place, left to right.. I shut the car off for a minute, restarted, and then it was perfectly fine.. As if nothing had just happened. Needle dead center. I'm completely stumped. And nervous.

[jperris]

You may have an issue in the engine harness. I can only think of a few things can cause your temp gauge to give an incorrect high reading:

1. Faulty temp gauge
2. Excessive resistance in the ground circuit.
3. Low resistance in the sensor circuit caused by faulty temp sensor or wire shorted to ground.

When you get erratic engine running that corresponds to temp gauge malfunction, it makes me think there may be issues with the engine wiring. Check engine bay for wires chafing on metal, check C191 and C101 connectors for corrosion or other damage.

Also, get a meter and check your charging system, checking for good charging voltage at the battery and at the alternator, do a voltage drop check between engine ground and body ground, and check for presence of AC voltage in the system.

[ringmeister81]

Problem solved... I hope. After reading over more and more posts, I finally inspected and cleaned the engine ground. It was filthy. I cleaned the contact points on the ground wire, the oil pan and the body. My power steering globe is leaking fluid and it made a mess on the drivers side, finding its way onto the ground wire.

After two test drives, I have not noticed any flicker on temperature gauge when running any combination of electrical components. The needle stays planted at a little under half. The engine has not shown any of its "wanting to quit" symptoms either.

I have noticed that the OBC lights do get noticeably dimmer when I touch the brake pedal or operate the blinkers... I suspect the alternator is on its way out. I already replaced the voltage regulator over the winter. I have no idea how old the battery is, so I will probably just replace it.