the flyin' scotsman

working on a 87 S4 and part of the project is the waterbridge gaskets and t.stat.

The PET listed part # doesn't state the temperature value and the new part shipped is 75C. 928INT lists the part number as 75C

The dilema, the thermostat I pulled off the engine is 83C and looks original?

dprantl

83 Deg C is the stock 928 thermostat. 75 deg C is lower than stock.

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

the flyin' scotsman

Sure seems that way Dan

I dug out the old t.stat from the 90 GT......83C

ROG100

Actually not correct according to PET (not saying PET is 100% correct). However PET very clearly states that from 87 to 89 that our cars used 928 106 129 16 (75C) and from 90 onwards used the 928 106 129 17 (83C). Up until 86 there was a choice of the 16 or 17.

the flyin' scotsman

thx Roger.

I sent an email with further detail.

James Bailey

Interesting.......wonder if that is WHY so many later model 928s the Owners think the temp gauge reads a bit high for "normal" ???

ROG100

I always thought that the 83C was the norm and that the 75C was the cooler choice. About 18 months ago some of my European and Australian customers pointed out that they wanted 75C and not 83C as 83C was not correct for the 87 to 89 cars.

James Bailey

The usual reason for running them a bit hot is for the reduced emissions. That need for higher temps is what just about killed the aircooled 911 and was a primary motivation for designing the 928. The 2.7 liter USA engines literally had thermal reactor cans under the exhaust ports to pass. The big problem then became all that heat caused to much stress on the head studs which promptly pulled out of the engine case. The cases are magnesium and could be "fixed" with casesaver threaded oversized inserts.

Became such a common problem that Porsche reverted back to aluminum cases with the 3 liters in 1978. Which is WHY the 78 > 911s are so much better cars ! Never EVER buy a 2.7 engine 911 if it has just a little exhaust leak Because odds are the heads are about to fall off !

the flyin' scotsman

It is indeed interesting.........I use PET 7.0 and for the '87 MY it lists 2 part numbers......up to '89 then '90 and above. There is no indication of temp. with either Porsche part number.

The car Im working on belongs to the original owner who has all records. The t.stat was never changed prior to my removal of the waterbridge and has the 83c stat fitted from factory....thats all I know .

ROG100

The part numbers are very specific in that the 16 = 75C and the 17 = 83C.
However here is the answer from Porsche - the current master parts list gives a supersede from the 16 to the 17.
So if we were to order a 16 75C thermostat from Porsche they would supply you with 17 83C.

Jim your explanation maybe exactly what happened.

SeanR

Just put the 75 in there and you will be fine. Won't make any difference on how the car runs. I've been running a 75 for 3 years and install them whenever a customer asks for one. They might have a smaller surface at the rear but it fits on the seal perfectly.

dprantl

Wow, that's a new one. Another 928 model year oddity. Could this thermostat change have anything to do with the '87's coinciding piston squirters... ?

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

Melo928

I have noticed that Wahler (83o) keeps engine cooler than Behr (83o), they have different opening curve. This could also explain some cars running warmer than other..

Basically you have three temperature choices: 75o, Wahler and Behr.

dprantl

This brings up another interesting question. Could it be that the '87-'89 928's have a different fan controller that turns the fans on earlier to go along with the 75 deg thermostat? PET lists only 928 618 418 00 from '87-95. Or maybe the thermostat choice was because of the cooling flaps.

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

dr bob

My mid-year production 1989 car (build12/88) came with the 83ºC thermostat from the factory. I tried the 75ºC thermostat for a while and it was just wrestling with the fan and flap controller in traffic. Just made the cycle between on and off bigger. Car did run a little cooler on the open road with the flaps open, but with the flap operating it didn't make much difference-- just cycled more.

So new regular 'stat is in and the flaps are de-fused right now. Makes for even bigger swings on cold (that's only SoCal cold...) days at low loads. The factory method seems to give the most consistent temp readings, never too cold, seldom over 190ºF indicated.