[928uk] Over-heating problem

[Richard Armstrong]

Paul
How long did you leave the 'stat' to soak?
Thermostats work within a range - The nominal 'Start to open' temp and 
'Full open.
Start to open temps vary, but 88deg is a very common one and I would be 
surprised if the 928 engine was far off this.
Full open is usually 9 deg above start to open and both values are +/- 
1.5 deg nominal (in reality it's more like +/- 2-3 deg, but the numbers 
are fudged!). It should take no more than 3 mins from start to open to 
full open. Quite technical for what is probably the simplest valve on 
the engine, and regulated by the percentage of copper powder to paraffin 
wax.
I know all this crap 'cos I have designed a machine to calibrate the 
thermostat elements which will ensure they open at the correct temp.

Failures occur when the little rubber seal in the top of the element 
fails and allows coolant into the element, which eventually flushes the 
wax out (fail closed) or the pin which is pushed out by the expanding 
wax sticks enough to stop return movement under spring pressure (fail 
open). Fail closed is obviously more dangerous, 'cos the engine will 
overheat immediately. Fail open is a pain 'cos the engine always runs 
cool, but will not damage the engine unless ignored for long - Fail open 
is by far the most common failure.

So now you know.
Richard



In message <1c9.188dd4a8.2dc5062e at aol.com>, PaulCulli at aol.com writes
>Hi all
>    Just getting round to fitting new thermostat, is there a correct bleeding
>proceedure for the cooling system??
>    Tested old thermostat, plunged into boiled water (probably about 90
>deg) didn't open so fingers crossed.
>Many thanks Paul and TRacy  (Platin metalic1982 S)
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