81 240d temp gauge doesn't work
 

My temp gauge stopped working today. I don't have a mech radiator fan, only the aux fan and it doesn't kick in now. The aux fan does work when hooked up directly to the battery, but it won't otherwise. I get voltage to two pins of the connectors behind the dash, but I don't know what they are for.
Any ideas of what should I look at?

Maybe the sender in the head? You dont have the standard belt driven fan? aux fan, you dont mean the one for the AC?:confused::confused:

hit your dash and see if it pops up.

I guess that's the a/c fan. I guess it was wired by the PO to kick in when it got too hot. How do I know if the sender unit is bad?
The needle moves a little when I put the key n the on possition.

I just noticed that the fan actually does work. Now I jut need to know how to fix the gauge.. how can I check the sender unit?

I just had this problem on my '81 wagon and it was the sender. I just pulled one off another engine I had out back. Others might have info on resistance readings but I can't remember what they were.

As I remember if there is NO resistance, its bad but I'm not sure, I would just pick up a new one, they are only about $10.

I changed the sender with a new one but made no difference. Any ideas???

Maybe find another gauge at the wrecking yard or eBay and swap it in.

The coolant temp sender(a NTC resistor type) will have the resistance readings(roughly) as follows:
37@ 100 C
50 Ohm @90 Celsius
67 @80
94 @70
135 @ 60
160 @ 50

The gauge is electric, so maybe there is a ground problem. the three gauges, clock or tach w/clock, spedo and the tri gauge on the left all overlap each other. this where each one grounds together. maybe there is some corrosion between them.

Pull the instrument cluster and lightly clean the contact areas.

there is also the ground connection I believe behind the inst. cluster where a bunch of brown wires come together.

remove the oil line with a 10mm and a 13mm.

do not start the engine with this line not connected. :eek:
you will be surprised with black oil gushing on you and everything.

Charlie

Good idea on the ground,

What you might be able to do is add a ground to the"gauge cluster" (mounting screws). I've never tried it but it might be possible without removing the instrument cluster. Remove the plastic panel above your knees, and have a look.