Fluctuating temperature gauge

[bovilexic]

The temperature gauge in my '98 ti occasionally fluctuates, rapidly moving from center/normal to the red zone, and then back again; sometimes it stays at or near red for a minute or two and then returns to center/normal.

This is what has been checked:
- Proper bleeding of coolant system
- Actual engine/coolant temperature has been checked with infrared sensor, while the gauge was reading "hot". All temps (in/out hoses, engine block, etc) show normal. Car is not overheating at all, it seems; so, thermostat not likely sticking closed.
- Sensors. Also both temp sensors have been replaced with new, with no changes.
- No water in oil, and no combustion byproducts in coolant
- Once warmed up, temp never drops below normal (so no stuck-open thermostat)
- No computer errors are thrown

Shop (and I) are stumped. Shop says it's possibly one of these issues:
1. Break (partial?) in wiring harness (from sensor(s)?)
2. Bad engine computer
3. Bad circuit board in cluster

Hard to test #1, and rather unlikely

Could try to find a cheap used computer, swap it in, and see if the symptoms go away.

New cluster is like $1100 installed, so of course something to be avoided if unnecessary.

Help!?

[bovilexic]

Or maybe just try another shop?

[BRADESTAR]

Seems like a dangerous assumption that you have going here, that it isn't overheating.

Have you done your cooling system in a while? Your Thermostat, H2O pump. Sounds like it is time. Maybe your fan is in and out.

[Ralliart10]

Its a blown fuse. Had the same problem and was fixed with a 20 cent fuse. So check all your fuses

[bovilexic]

Originally Posted by Ralliart10

Its a blown fuse. Had the same problem and was fixed with a 20 cent fuse. So check all your fuses

A blown fuse could cause an intermittent problem? My gauge is typically solidly in the center, and just very occasionally jumps rather quickly to the right, and then back again...

But, I'll have a look at the fuses, just in case :-)

[bovilexic]

Originally Posted by BRADESTAR

Seems like a dangerous assumption that you have going here, that it isn't overheating.

Have you done your cooling system in a while? Your Thermostat, H2O pump. Sounds like it is time. Maybe your fan is in and out.

Hmm...pump and thermostat have maybe 40-50K miles on them...probably cheaper to replace than a cluster, but the measured temperature of in/out hoses showed normal operating temperature, even when gauge was acting wonky...

[Dubster1]

Cant you get a secondhand cluster? it should cost less than a tenth of what youve quoted and a novice can do a swap in less than a hour.

[bazar01]

Had the same scare with my 1996 M44 TI.
The temp gauge started fluctuating from middle to 3/4 and back to middle but not red zone. Did this a few times while idling.
I immediately parked it home.

I performed some tests.
Sensor disconnected, gauge reads cold.
Took a sensor off a spare engine and plugged it into my 96 and heated it with a lighter, gauge temp went up.
I installed the spare sensor.
Drove it around the block with the ac on and gauge stayed at the middle.

I will get a new sensor and replace it later.