I have a BMW 324td (E30), largely similar to 325 I believe, and recently on
long journeys the temp guage is behaving strangely. For a while it seems
fine, hovering arouind the middle. Then can rise up to 3/4 but then coming
back down. On occasion or if in traffic the needle seems to dance around
somewhat randomly but largely going up until it reaches the red. There is no
emulsion on the filler cap and the water level doesn't seem to change. I've
stopped a couple of times but have never seen it actually steaming. I find
this a little disconcerting as I don't know if the car is actually
overheating or if its a faulty temperature reader, when I've felt the pipes
they are hot though.
You need to work out if the sender is being truthful... If it's
twitching, it sounds a bit odd. Unfortunately a normally happy working
temperature for a car engine is also what you'd call hot.
Ignoring the fact that the sender sounds a bit iffy, when you say the
temperature get's to 3/4 then goes down, does it go down very
suddenly? If so, change your thermostat, your current one is sticking.
1 - sending unit - change it to be sure
2 - possible shorted wire
3 - possible bad thermostat - change it to be sure
4 - possible air in the system. this can be cause by a bad radiator cap.
change it to be sure.
All the above are low-skill tasks to replace low-cost parts. It won't
hurt you to buy the parts and change them all out. Replace the coolant
too, if you have never done so.
This sounds like a gauge problem to me.
The temperature gauge in my 318i acted like this when the gauge was failing.
The next time it acts up, just try giving the instrument cluster a sharp rap
with your knuckle to see if it has any effect.
When my gauge was going out sometimes this would cause it go back to normal
and sometimes it would jump all the way into the red, the important thing
being that tapping on the instrument panel would cause the temperature gauge
to change quickly.
Had the same problem with my E30 325i,very simple to fix.Remove instrument
cluster,removed the cable from the temp gauge,clean off and refit.
Fault is caused by a bad contact,cleaning and roughing up the contact
I had this done by an independent specialist,who after i told that I thought
the fan,sender etc was faulty just asid NO dirty contact and only charged me
a few pounds to repair.
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