Temperature gauge swings wildly
 

I have a 190e 2.3 1988
the temperature gauge acts normal, then bounces up and down rapidly (within a second or two) then back to normal. Nowadays it bounces either up or down and stays there, like past the redline as far as it can go.
Any ideas really appreciated, this is my baby here please help.

sensor trouble
 

I drive a 94 200E, so this info might not be 100%, but worth a look anyway ....

The 110deg sensor on my car went bad. I opened the faulty unit to ascertain what could cause the trouble (destroyed it in the process - but it was shot anyway)

It's a mechanical device for switching the aux fan on at 110 whilst it also houses the resistive element for the temp sensor (a three-pronged sensor with 110 stamped on the side).

What happened was that the switching element broke off inside and fell in such a way as to periodically shorting with the temp probe, whilst sometimes causing a short that popped F7 (the aux fan fuse) !! When shorting to the temp probe I got 120deg + on the display whilst it was OK otherwise ...

changed switch / sensor - all fixed. I pulled the sensor as a last resort when testing for bad wiring to the temp sensor proved nothing. A dead short (i.e. chassis earth on the sensor wire) shows 120deg + whilst no contact shows a cold engine - on the 102 engine anyway.

maybe this helps ...

L

Does it jump up like it could be a broken wire? How old is your thermostat? I think they should be part of the scheduled maintance. If it is the real engine temp the thermal shock is bad on the radiator and head gasket. I've seen a varity of failures of thermostats and this could be one of them.

Machnumber2,

za_w124_200e is likely correct. A flickering guage needle is highly unlikely to be an actual temperature change. For the most part, a quick, less than a second duration transient of 10 or so degrees would not even show up, much less cause the needle to flicker. The response time of the boss, sensor housing and sensor to temperature changes is much longer than a flickering of the needle you described.

I would start with the sensor by checking its response as the engine warms up. Disconnect it and see what the guage does, then record the signal as the engine warms up by checking resistance, and see if it suddenly goes to zero or infinity. If so the problem is in the sensor. If not, it may be in the wiring or the guage in the dash.

Hope this helps. Jim

finally found the problem
 

I finally discovered the problem tonight (after replaceing 3 temp senders/switches, the battery and the overvoltage protection relay)
As I was driving I noticed that the temp gauge movement sometimes was in sync with
bumps that I would go over on the road, in other words if the car experienced some movement, the gauge would react at the same time by jerking up and down.
I poped the hood, had my wife watch the temp gauge in the car, I grabbed some wires from the temp sender and pulled them repeatadly, when I did she noticed that the gauge moved when I pulled on the wires. I figured it was a short. I took off the air cleaner, light up the area with a flash light while pulling the wires to expose them, after a bit sure enough I saw a joint with copper wire exposed. I cut off the damaged portion of wiring, spliced it and it works great now. Whew glad my car is back to its old self now. Hope this helps somebody someday.
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