Weird temp issue

[Sps]

Stock motor rebuilt with new water pump and fan clutch. If I take off when the motor is cold, the temp will climb over half way and then the gauge bounces all around. It gets really twitchy and goes from the first line to well over half way. It will stay hot and needle will be past the halfway line until the engine cools again after I let it sit parked.

If I let the car warm up and let the needle get past the first line then drive really calmly for about 2 miles, the temps will stay low between first and middle line. At that point I can drive it like a rental with no issues.
Any ideas?

[jlevie]

How fast does the gauge bound around? If really fast it would sound like an electrical problem with the gauge, but if much slower a bad thermostat or air in the cooling system could be the cause.

[Sps]

How fast does the gauge bound around? If really fast it would sound like an electrical problem with the gauge, but if much slower a bad thermostat or air in the cooling system could be the cause.

Thanks for the reply. It bounces fast. I would have believed it was an electrical issue but it will only do that if I don't let it warm up for at least 5 minutes.

[jlevie]

It takes a few seconds for the coolant temperature sensor to react. If the gauge is moving faster than that it is an electrical problem.

[rex]

My temp gauge started jumping around like crazy, and I did some reading and found likely causes are a nut on the back of the gauge that needs to be re-tightend and/or cleaned or even replaced (can get corrosion which makes it have a bad contact), or another thing that can cause it is the SI batteries going. I was planning to pull my cluster and check it out but it stopped doing it and hasn't since. Go figure

[Sps]

My temp gauge started jumping around like crazy, and I did some reading and found likely causes are a nut on the back of the gauge that needs to be re-tightend and/or cleaned or even replaced (can get corrosion which makes it have a bad contact), or another thing that can cause it is the SI batteries going. I was planning to pull my cluster and check it out but it stopped doing it and hasn't since. Go figure

But if it is an electrical issue, why does it not happen if I let the car warm up completely? It will only do this if I take off right away. And you can feel that the motor is running hotter also.

[rex]

But if it is an electrical issue, why does it not happen if I let the car warm up completely? It will only do this if I take off right away. And you can feel that the motor is running hotter also.

I'm new to working on cars, so I can't give you a good answer. I would chalk that up to these cars being old and 'shit happens'. Car may be running hotter but its pretty unlikely (impossible?) that the engine temp is actually swinging up and down as fast as the gauge is moving.

Pulling the cluster and checking on the ground connection nut is probably the easiest/cheapest thing to test out

Well its easy unless your PO put some kind of thread-locker onto the steering wheel nut, as mind seems to have done, I still haven't been able to get it off.

Here's a pic, the nut I'm talking about is to the lower left of the blue connector

[Sps]

Thanks for the pics. I am familiar with the ground issue and that is something i will do in the next few days. Another weird thing, Iif you try to start the car in gear with the clutch pressed the car takes forever to fire up. Hahahaha, what a mess.

[noid]

Check your chassis to oil pan ground.