drifting temp gauge

03 530

This might have been happening for a while but I've just noticed it during the last couple of weeks. The temp gauge randomly drifts slightly (maybe just a bit over 1/8") to the cool side of 12 o'clock then returns to normal. It never goes to the hot side of 12 o'clock. There doesn't seem to be a pattern ( e.g. based on speed, acceleration, idling). The car warms up normally and the heater pumps out the good stuff as normal. Unfortunately I don't have the high cluster so I can't check the actual temp. My thoughts so far:

- a "lazy" thermostat that's staying open too long
- a clutch fan that's not properly reacting to the ambient temp. I've done the newspaper test on it and haven't noticed any apparent problems.
- the gauge is acting up
- "they all do that"

Appreciate your thoughts

Unlock the instrument cluster and monitor actual coolant temperature (test 7). If it's steady, the sensor side that feeds the cluster may be bad.

When the cooling system is operating properly, you'll seldom, if ever, see the pointer move around.

This morning was particularly cold and this time my temp gauge wouldn't go up to the vertical at all. It stayed at about 1/8" to the cool side of 12 o'clock for about 10 miles. I pulled over and let the engine idle (to check the fan clutch). After about a minute of idling the gauge crept up to the 12 o'clock position and stayed there for the rest of my trip.

On my way home the gauge went to 12 and stayed there rock solid for the whole trip. This is looking more and more to me like a sticking thermostat. What do you think?

The gauge is not that accurate, more of an indication. So I'd follow edjack suggestion and unlock the cluster and monitor the actual coolant temp. Will give you a much better diag. Thermostat is most likely cause but best to check whats going on.

I am presuming the rest of the cooling system is in good order? You don't want to replace thermostat for other parts, e.g. water pump, to fail a week later (been there and done that...)

Ok looks as if the problem might be electrical. Found this thread that pretty much mirrors what I've been seeing.

http://www.bimmerfest.com/forums/sho...d.php?t=650846

The random nature of the problem "seems" to point to a loose or dirty electrical connection. Cleaning the connector to the temp sensor and checking the wiring is an easy first step that might do the trick.