j.kenzie@sbcglobal.net

Hi,
A couple of years ago, I replaced my thermostat. Because it was a hot summer, I decided to put in a 75 degree C. unit. I was wondering if this unit could cause: rich running due to lower temp, poor heating system performance due to lower temp? If running rich, will I have more power? Any other problems? I am thinking I will put in standard 83 degree unit.
Thanks,
Dave

hacker-pschorr

Only if you install it backwards.

I have the colder 'stat in both of my cars (79 & 81) the cut-off for the hot maps is below 75C anyway, so no issues with the fueling.

Randy V

Only positive benefits after I installed the cooler t-stat.

Lower operating temps and less pinging.

FredR

Dave,
I have used the 75 C thermostat for quite a number of years, because it was thought by some to be a good thing. In a hot climate it is not really a issue in that the system heats up until an equilibrium forms. Later on after a number of projects to improve cooling, I find that during our [mild] winter conditions the motor struggles to warm up and I get the impression that the motor does not fully loosen until the gauge shows 85C [coincidentally the stock thermostat opening temp]. Where you are 1 bus stop short of the north pole I do not think I would run the 75C unit at all- just ensure your cooling system is clean and functioning correctly. Indeed, now our cool season is coming around I will probably ask Roger to send me an 85C unit in my next order.

Regards

Fred

Dictys

I had the 75c and changed it back to the 83c thermostat, the 75c was for some reason much more restrictive to the flow. My car runs between 83-86c whatever the outside temp and engine load.

WallyP

The 928 engine is designed to run at 85-90 deg C.
If your car overheats with the 85 deg thermostat, something is wrong, and installing the 75 deg thermostat is a bandaid.

Tails

+1 on Wally's comments.

Combustion chamber temperature, flame spread and degree of complete combustion of fuel at ignition, exhaust gas emissions such a NOx etc., etc.

Tails 1990 928S4 Auto

hacker-pschorr

Yes lowering the operating temperature will lose some efficiency, but it also lower the knock threshold - which in my opinion is a good trade-off.

Which is why Todd with his twin turbo runs without any thermostat (modified t-stat bridge, you cannot just take it out). And he controls the temp with his fans to keep the engine around 170F or so.

FiveElements

I think it depends on how aggressive you drive your can and the climate you are in. I'm on Calif and its regularly 90 to 100^F. I switched to the 75c thermostat because I like to run the car a bit more aggressively. But in the winter it's probably better to go back to the 83^ one.

dprantl

I've also been running the 75 deg F thermostat in my supercharged GT. It gets up to 100 deg F with high humidity down here and I also find there is a reduction in knocks with it. It also gets down to slightly below freezing here, and I drive my 928 all year round. I don't have any rich running or heating issues in the winter.

Dan
'91 928GT S/C 475hp/460lb.ft