968TopDown

I've had my 6-speed 968 into the shop a couple of times for the same issue and it's happening again, so I wondered if anyone might have an idea of what they should be looking for.

The temperature gauge needle jumped up into the red a couple of times, and I would pull over and turn the car off. Within a few minutes the gauge would show the normal range again. Then it started acting totally disconnected from plausible measurements, such as the needle bouncing when I went over a bump. I took it to the shop and they replaced the thermo switch and the cooling fan relay, plus tightened the connection at the temperature gauge sensor. From their notes, it looks like it actually was getting too hot without the cooling fan not coming on.

But not long after I got it back, the gauge was acting the same way. I took it in again and they replaced the coolant temp sensor.

Now the gauge is acting up again. The cooling fan does run now, so I believe it could be just a sensor or gauge, and so I've driven it for about 10 minutes at a time. The first few times the needle would start in the red, but after the car warmed up, it would drop to the normal range and appear to work correctly. But as of yesterday it just stays in the red the whole time, so I'm going to take it in again rather than risk overheating it.

Any suggestions, or should I just tell them what's happening and hope they can figure it out? Could a short be damaging parts?

I take it to a Porsche dealership and I do believe they do excellent work. They've always kept it running great. I think they have one mechanic trained to work on the 968 so it can take a while to get an appointment.

LM964

Would you not want to rule out the sensor first? Easiest to test/replace. Don't think you need to worry about needing a Porsche independent specialist to get the sensor checked (auto electrician can take a reading on when the sensor is providing a signal or not and to check for firm connections inc ground). Maybe try a reputable European workshop. If a dicky gauge then that's a bit more hassle as I wouldn't want just anyone pulling out the console. The water temp sensor is cheap - anything between $50-$120 it seems when looking up. Likely something you can replace yourself. Give the whole cooling system a flush through a couple of times then refill with coolant mix.

931guru

Test your gauge in the car.

https://www.clarks-garage.com/shop-m...19.htm#coolant

JimV8

I believe theres a clue in the bounce of the gauge that leads me to thinking theres a high resistance on a ground.

Zirconocene

I agree with @JimV8 , it sounds like there's some electrical tomfoolery afoot.

Good luck

968TopDown

Thanks for the responses! I do have a multimeter and the workshop manuals for the 968 and 944, but I couldn't tell where I should be looking. That link from @931guru is excellent. I'll check the gauge and grounds this Sunday and report back.

oppositelock

The attached might help. Also, get a infrared temp checking gun. You can check to make sure it really is or is not overheating. Point it at all parts for the cooling system.

weberlukas74

Getting a cooling system pressure test can find leaks or weak spots causing overheating.
Also, I’d suggest checking for frayed wires or loose connections in the wiring near the temperature sensors and gauge.
Plus, doing a coolant flush and refill could help rule out any lingering coolant contamination or air pockets affecting temperature readings.