I've got a 92 240 with a dead temp gauge. I took the cluster out today and tightened all the connections and familiarized myself with the unit. No change.

I've read that a bad voltage regulator could cause issues with the gauges not working but the gas gauge works fine. Wouldn't both be dead if the regulator was bad?

Mechanic briefly looked at it when it was in for something else and said that it was most likely in the cluster itself.

Any ideas?

Oh, and what the hell is that little button on the right hand side of the cluster opposite the clock reset ****?!

 

the button is probably for a service light (my 92 740 has one). comes on in 5000 miles, push button to reset.

the temp gauge is on its own sensor on the engine, not the same as the one that the ECU and ICU use. its possible that sensor wiring is funky, or the sensor itself is dead (wiring is more likely the problem).

you could unplug the sensor, and hook up a 5k or 10K ohm potentiometer (ask an electronics friend) to ground, and the temp gauge should respond to the pot. high resistance is low temp, low resistance is high temp.

 

Where is the sensor?

 

its one of three sensors stuck in the side of the head under the intake manifold. the order of these sensors is not consistent from car to car, but generally the front most one is the 2 pin engine ECU/ICU coolant sensor, then there's the anti-knock sensor whcih is flat and has the single wire on the side, then towards the back is the temp gauge sensor, which has a single wire.