325i Convertible - Temperature Gauge High Reading

[Hartysbeemer]

Once warmed up after a few miles the gauge seems to go into the red stay there and then come back down again but sometimes stays in the red.
I don't think the engine is overheating, all runs ok, thermostat replaced recently, no white smoke from exhaust, perfomance is fine. Oil is ok so no signs of head gasket failure.
Anyone any ideas - thought about the sender unit but don't know where it is, also is there a way to test the gauge ?
Any help gratefully received ......

[jacko]

Sounds like it could be an air lock. Have you got a bleed screw on the thermostat housing, this usually does the trick for mine if the system is disturbed for any reason such as new thermostat. Does the heater blow hot air when the guage is in the red?

[Hartysbeemer]

Thanks but I have checked the bleed screw and coolant runs clear, heater working fine lol

[jacko]

You say the oil is ok so not head gasket failure. The trouble with head gaskets are that they can fail in so many ways, they dont always mix oil with water or visa/versa.
Have you had a sniff in the expantion tank for exhaust fumes.
Also there could be loose nut on the back of the clocks causing this IIRC but somebody more in the know should confirm.

I really should proof read my posts!

[daimlerman]

Gauge sender is the brown one,close to the top hose.Blue sensor is for the ECU,BTW.
So,engine is full of coolant,been bled of air and still runs hot?
Is this running hot when stationary in traffic?
Dropping back to 'normal' when on the move?

[Hartysbeemer]

Thank you.
Yes guage goes into red when stationary. Forgot to say the viscous fan is new. Sometimes goes back to normal, but other times seems to stay in the red

[daimlerman]

Now with a new viscous coupling fitted,a new thermytwat fitted,that only leaves circulation and airflow....I would be inclined to suspect the radiator next,Mr Moore once advised that these should be 100,000 mile service items!
Circulation can be checked by seeing if coolant is being returned to the header tank,but I feel that a failing pump would be noticable by a dribble down the front of the engine or side to side play in the fan.
Of course,if your new viscous is not working properly....
With the engine hot and the thing engaged,try feeding a rolled up newspaper into it,it should be shreaded,if it stops the fan you have found your culprit!

[Hartysbeemer]

Thanks - I'll go and buy a paper !

[Hartysbeemer]

Thanks guys for all your help on this one. Problem solved, gauge steady between 1/4 & 1/2 way even in traffic. The nut at the back of the guage was indeed loose.
Am a happy bunny now

[lawriejones]

Another satisfied customer.