325i temp gauge sudden new normal position

[john <j.s.smith@xxxxxxxxxxxx>]

Happy new year all!

The temperature gauge on my '89 325i has (since 2 days ago) taken up a
new "normal temp" indicated position. Up until now, in hot or cold
weather it has always indicated about 1/8" below centre position - at 
all road speed including sustained 70+ mph driving. Sometimes when
waiting at the lights or in traffic q's it would creep up to say 1/4"
above centre - never more.
The new "normal" temp is suddenly 1/8" *above* centre position. 

Not wishing to be paranoid about this but about 4 years I had a complete
cylinder head failure (the thing went "porus") and I completely replaced
it ($$$£££)! At that time the first indication was that the temp gauge
went almost into the red quite suddenly and coolant loss escalated
rapidly.

I'm hoping the same thing is not going to happen again! SoO far I've
checked:

- - there are no visible leaks
- - no loss of coolant (as seen in expansion tank level)
- - replace expansion tank cap
- - observed expansion tank level goes up and down as expected while
engine warms up
- - water pump drive belt tensioned ok
- - interior carpets dry so don't think heater is leaking
- - no signs of froth in rocker cover
- - no signs of bubbles in expansion tank
- - cooling system seems to be holding pressure (when loosen cap, can hear
hiss)
- - viscus cooling fan seems ok and is rotating as expected

Given the above, what are digester opinions of the sudden step in gauge
reading? 
So far I can think of:
- - Gauge or sender has suddenly developed some fault
- - thermostat failing (sticking slightly closed)
- - Water pump failing
- - [And now the "oh no's"...]
- - head gasket failing
- - don't want to mention cyl head...

With the previous head failure, a compression test showed two adjacent
cylinders at exactly the same reading - and this was where the head had
failed. I haven't done a compression test yet...

The engine is runnimg just fine - idle and accel... but I do see a cloud
of white smoke under hard acceleration - sometimes! This happens even
more if have been just driving at a slow speed for some time then
suddenly accelerate. 

================================================================================================================
I see in Bentley there is a very useful tool that can pressure-test the
cooling system. Have never tried this. Anyone have any practical
experience of using one of these for diagnosis of the above? 
=================================================================================================================

Thanks very much.

- -John



 



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