Oil Thermostat

[Bob Goding]

Funny that larkja's post re his oil line problems should surface at this time, as I have been studying the 911 thermostat over the festive season.
As was mentioned,I had read that the Mocal Thermostat was
inferior as it does not have a pressure relief valve.
I asked myself [as I was the only source of info available at the time!] ---why does the system need one, and what and how does it relieve?
I had assumed that it was to avoid over pressurisation of the
oil cooler.
But high oil pressure would only occur when the oil was cold
and the temp. bulb was bypassing oil back to the tank anyway.
At startup,the scavenge oil would go thru the 'thermostat' straight back to the tank,so how does the pressure valve relieve?
My old 77 doesnt have an external cooler[yet] so I cannot do a visual.
I did manage to get access to a thermostat from a 3.2 964
and the layout is quite different to the earlier cars, but it does
not appear to have a pressure relief valve[unless it is part of the
thermo valve, which appears quite large,from the outside].
I was not permitted to open it up and have a look! but I did observe that the fittings were screw in steel which shoud avoid the hose removal problems with the earlier unit.
Anybody like to give us the 'Course of Approved Training'!
on this aspect of the 911 oil cooling system?
Thanks Bob

[Fishcop]

I'll be using the mocal as I didn't see where the pressure relief would be relevant in a well functioning system.