Temperature gauage PING!

[laforzaland]

While driving to a local car show my 1980 Fiat Spider (FI) was running well, no issues. After a 30 minute drive, I turned off the engine and let the car sit for a good 30 minutes. When I returned and started the car, the temp gauge immediately PING'd into the red zone. The same thing happens when the key is turned to the ACCY position prior to starting. The car runs fine. There is no coolant spaying or hoses bursting. The electric radiator fan turns on when the coolant reached the proper temperature.

I decided to drive the car back home since the engine was responding positively. While driving the temp gauge dropped back down to 190° for a minute then jumped back into the red zone.

I recently replaced the radiator thermal switch without completely draining the cooling system. I did top off the coolant after the radiator switch was replaced. I'm not sure if this has anything to do with the temp gauge display???

Has anyone had a similar experience? I can burp the cooling system and/or dive in with my multimeter to test the wiring, but would welcome any advice prior to blindly starting to troubleshoot. Any suggestions???

[daved]

I seem to recall reading the gage was designed to suddenly peg all the way to the right if the temp. got past a certain point to get the driver's attention. Don't find that in writing anywhere & not sure if that is what you are describing.

[laforzaland]

I agree with what you are saying and am aware of that. My issue is that this never happened before, now after swapping the radiator switch the gauge is acting funny.

[ORFORD2004]

Play with the wire to see if the needle jump because of a wire contact to body.

[laforzaland]

Thanks... will do.

[courtenay]

There are two temperature sensors located in the centre of the head between the spark plugs. On my '80 fi the one nearest the front of the engine (i.e. radiator end) is the sensor that pegs the needle and the one near the firewall measures the engine temperature shown on the gauge. You should disconnect the wire to the front sensor and see if the gauge which will stop the gauge from pegging but will still give you the actual engine temp. You will need to replace the front sensor if you still want the "pegging" feature to work. I've been running my car for about 4 years with that sensor disconnected. Just make sure I'm closely monitoring the engine temp shown on the gauge.

[laforzaland]

Thank you!

This is exactly the step-by-step advice that I was searching for. I appreciate your time and for sharing your knowledge.

[megaul]

Had the same, been searching for ages with experienced mechanics

Check for a blue housing under the dash near the brake paddle that looks like a fuse. It's not, it's a shared resistor for the gauge. Clean that thourougly or replace the resistor and the needle should do what it's supposed to do.