Bertrand Daoust

Last October I did a fun run here with our PCA division.
If I remember well the temperature was around +5°C at the most.
The temp. gauge never went to the first white line! Maybe around "75".

That's quite low for me.

Didn't use a temp. gun but my gauge is quite accurate I think.

I then started to wonder if I did the right thing when I put the cooler thermostat!

Before I changed the thermostat (I had a 83° thermostat before), I remember the temperature was always over the first white line. About at "85". And a bit higher on warm days. 30°c. (I know Fred this is a cool day for you... ) but always under the second white line ("90").

I now believe, like you mentioned, that in a cool climate like what we have here, a 83° t. is the way to go to have the engine to run at its specific temperature all the time.

Thanks Fred and all.

Mark Thornton

I have heard the term "Burping" the system exactly how is that done? BTW I own an 85 5 Speed car

Bertrand Daoust

Good thread on this here:

https://rennlist.com/forums/928-foru...ng-system.html

jcorenman

I just had this conversation with Greg Brown a couple of days ago. I've gone back and forth a couple of times between 75c and 83c thermostats, but Greg recommends the 83c (at least for 87+ cars) for a couple of reasons. First is that the fans and flaps are designed around the 83c thermostat, and work in concert to hold a constant temp. With the cooler t-stat they argue continuously. The second is that the engine is happier and runs more efficiently at the higher temp.

I don't think it matters for cold versus hot climes... if the combination of heat load, air temp and airflow exceeds the system's capacity then the engine will overheat. At the limit the t-stat is certainly wide open, and when it began to open makes no difference.

Here's our dash (90GT) this afternoon, Sharktuner said 80c, cool weather (5-10c) and quite stable up and down the grades on I-5. Flaps and fans all working.

Bertrand Daoust

"...The second is that the engine is happier and runs more efficiently at the higher temp."


I like that.

I will definately go back to the 83° t-stat next spring.

Thanks Jim.
Very appreciated.

SeanR

I agree with what Jim just said. On the cars with the digi dash the reading is a bit more accurate. One thing I'm finding on the earlier cars is the condition of the foil on the clusters and condition of the engine harness is making all the gauges read different than actual. If you pull your 14 pin connector and see green corrosion on the blue/green-blue/yellow wires, you are getting resistance and the gauge isn't going to read correctly. The readings due to the foil are a different game as there is generally no corrosion but contact issues.

I've not seen a huge variation on the digi-dashes like Worf but I've also only had two that had faults there. One I replaced the circuit board (last one in existence) and one I just told the guy that until we can find another board, to not lose any sleep. Checked with an IR gun in Texas heat he was running 190 at the sensor.

FredR

Bertrand,

No matter how long we own these things as long as we continue to learn from each other we will be in good shape. I went to the 75C thermostat thinking it made sense but eventually concluded it was anything but. So with your numbers I suspect you might have been running a bit richer than it should but then I do not know if the O2 sensor [you probably have] would correct back to stoich- I suspect not whilst still in the warm up zone.

Interesting comment from Jim confirming what I said about the fan programming.

Not sure if my motor is typical [I suspect it is] but I can clearly tell when the motor is heated up by the way it wants to rev. Until my temp gauge goes over 80C I nurse the motor and limit revs to a max of 3k to 4k and never push max revs until the needle is where it should be. Until the motor is fully warmed up it simply does not feel like it wants to rev - whether that is just ingrained in my psyche or whether it is a mechanical fact I do not know for sure.

We had a chap in the UK who was quite knowledgeable but somewhat arrogant who many years ago commented about how long it took his 928 motor to warm up-15 minutes or something daft like that- something he put to down to the UK climate! I politely suggested he was talking a load of bollocks and to check his thermostat and specifically the rear seal. After trying to tell me I did not know what I was talking about, when others suggested he might do well to listen- he did and found out I was spot on with my analysis. After rectifying the problem he found his 928 warmed up in no time [surprise surprise]. Your system works predictably but arguably is technically a little bit deficient - his system did not work and he could not work that out.

One has to wonder just how many folks have similar issues but are not smart enough to understand or at least ask a question. I have seen a number of posts where folks state how cool their motor runs thinking somehow that the lower the better- hmm!

worf928

Not what I wrote. Post-'89 variation I see is GTS only. But, GTS garage queen sample size is 4. Other than GTS I would say that the digi-dash temp guages are spot on.

UKKid35

Good call, and if you are still concerned about engine cooling I recommend retro-fitting a GT type oil cooler. In my experience it is far more efficient than the side tank cooler. There are no concerns about it slowing getting the oil up to temp because of the oil T stat.

Just realised that you have a '91, so your car should already have the separate oil cooler...

curtisr

I don't have access to my 928 Owner's Manual but my '87 924s (2.5L) OM says it is perfectly normal for the temp to approach the 3/4 mark. If I don't like what I see, I just turn the AC on.

SteveG

Not to ignore the rest of the discussion, but I think Dr. Bob has reduced this to its base. If I understand it correctly the only difference the thermostat makes is how quickly the engine warms up. In a hot climate, you might want want full cooling sooner, if it's 100 F ambient, taxing the engine with A/C, and/or a hill and or not moving through the air mass, the thermo doesn't matter. As a generalization, it seems Porsche didn't want it to warm up too quickly.

worf928

The lower-temp thermostat will lengthen the time it takes to get the engine to its designed operating temperature. This much is certain.

One thing that I've always liked about the 928 is that on a cold day you'll get heat at the vents about two blocks from your house. It make take a while to get to 195 but it gets to ~1/2 pretty quickly.

James Bailey

As was pointed out....no need to burp the 928 system but if squeezing the hose makes you feel better go for it....just recognize that it will clear any air bubbles whether you squeeze it or not