RE: 325i temp gauge sudden new normal position

["Fadeev, Alex" <alex.fadeev@xxxxxxxxxxx>]

john [mailto:j.s.smith@domain.elided] wrote:
> 
> 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.

John,
Make sure your thermostat and your auxiliary fan are both OK. The coolant
temperature should not creep up much, if at all, at the stop lights.

> The new "normal" temp is suddenly 1/8" *above* centre position. 

I would vote for a bad $10 thermostat sticking partially closed.

> 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

could be, although a flaky/jumpy temp gauge manifests itself by
intermittently indicating wildly different temperature readings.

> - thermostat failing (sticking slightly closed)

gets my vote.

> - Water pump failing
> - [And now the "oh no's"...]
> - head gasket failing
> - don't want to mention cyl head...

All are unlikely. 
When was the last time you replaced the water pump? If during the last
t-belt change, it should be fine.

> 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. 

Are you loosing any coolant? If not, don't worry about it.

> ==============================================================
> 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? 

It is nothing more then a hand pump. You manually create pressure in the
cooling system to induce leaks. It is useful only if you are loosing coolant
and want to pin point the source of the leak.

good luck,
alex f

------------------------------