hacker-pschorr

Well....in order for a lower temp t-stat to work properly the ECU and fans should really match. Not that it cannot make a difference without those changes, it's not doing it properly IMO. I would need to see temp compensation map first in order to remember where it changes.

However...I would first make sure everything is perfect stock. I've flushed out a couple radiators from cars that were otherwise in great shape, you would have been surprised to see the gunk that came out from various forward and reverse flushings.
Issues at low speed / idle can indicate fan issues, doesn't seen to be the case here.
Running lean can also cause engines to run hot. I don't think this is very common with 928's though, but still a possibility.
Clogged CATS, but if they were that bad I'm sure you would feel it with the power. Also not a terribly common reason for 928's to run hot.
The t-stat installed could be faulty and / or the seal behind it.
I'm sure I'm missing a few things to check.

I'm not a big fan of modifying things unless I've verified everything is 100% perfect.

FredR

if it was a good idea to run a 75C thermostat do folks really think Porsche would not have worked that one out? I cannot comment on other motors but my motor needs to get warm before it feels "loose" and that seems to happen when the gauge indicates 80C or greater so it makes no sense to try to run cooler.

I have tried a 75C thermostat and in really hot weather it makes no real world difference but in cooler season weather it does make a difference and it is not a "good difference" as I am concerned.

merchauser

Fred, I completely agree, however, 1987-1989 cars specified 75' T stats? can we say that "essentially" the 5.0 motors after 89 are the same?

Speedtoys

No, cuz they're not.

Cams, and displacements started changing.

merchauser

FWIW: this is from the 928 motorsports online parts list:

Application: All Porsche® 928 1978-1995

The Problem: The Porsche® 928 is susceptible to overheating as the radiator ages, or when modifications are made to increase its HP (and heat) output. This is especially true if the car is kept in hotter climates.

The Solution: Replace the stock 83°C thermostat with this brand new thermostat at 75°C. The lower temperature opens the t'stat earlier, and lowers the operating temp of the engine. Made in Germany for Porsche®. A new o-ring to seal the housing is included!

merchauser

not sure I follow; how do those items factor into T stat values?

hacker-pschorr

Hotter engine = more efficient, better gas mileage & emissions.

soontobered84

You DO know that they are trying to sell you parts, right?

Speedtoys

I dunno, i'm not the the engineer that decides those things. And i'm still learning that when I overthink how things should be, I end up discovering that I shouldn't be thinking about it.

You asked if they're the same..they're not.

SeanR

Speedtoys

So a cooler thermostat cleans out the old radiator returning it to as-new performance levels?


...think about that. If (the vendor stated problem) you're overheating because **** radiator, why will moving energy into it _faster_ make it also cool better?

Why would a 500Hp car on stock hardware have no problems then?

hacker-pschorr

LOL - Ok, back on point here guys.

It is funny though.....

Bertrand Daoust

This.
The faster you get to the right operation temperature, the better it is.

worf928

Actually it is almost true. By adding one more sentence it becomes completely true:


Under some conditions a 'cooler' thermostat may prevent the core engine temperature from reaching the designed operating temperature.

... and thus 'longer' becomes 'infinitely-long.'

There is of course a corollary:

If your car's engine is operating at a temperature in excess of the designed operating temperature, fitting a cooler thermostat will not lower the operating temperature.


You do, however, raise the nuances of this topic to the foreground.

It is most correct to omit 'cooling' from 'cooling system' from that. The 87+ 928s (I won't opine on the earlier ones) when they are in good repair and have the undertray fitted, have sufficient heat radiation such that, at speed and in moderate climate, the 83-degree thermostat is barely open and the engine NTC-II temp is around 175-185.

If you fit a 75-degree thermostat then, yes, of course the core temp will be a bit lower because you are adding heat exchange capacity.

But, even at 185 degrees the 928 engine isn't 'completely' warm yet and thus you're running the engine at a temperature lower than what Porsche intended.

On the subject of what Porsche intended, I looked through the TSBs, Service, info, etc and didn't find a reference to a thermostat change. And, my 15-year-old version of PET that would show the part numbers before supersession is non-functional. I don't disbelieve a change for '89 from '87-88, but I'd like to know the provenance. If at any point I knew about this change I have purged it from memory.

And that is consistent with the above: you engine never got 'warm.'

Again this is completely consistent. If you install a thermostat that doesn't open until a temperature that is higher than the designed operating point then you can expect the engine to get 'too hot.' Of course, I could put a 110C thermostat in and I'd be fine as long as it was about 50-degrees out and I never strayed from about 75 mph.

Unless someone can show that the 75-degree thermostat allows more water to flow from the radiator to the water bridge than the 83-degree thermostat when they are both fully open, then the only possible effect of a 75-degree thermostat is to keep the engine below its designed operating temperature for a longer period than the 83-degree thermostat.

Let's face it: this topic almost always comes up because someone has an issue with the cooling system and thinks a lower temperature thermostat will fix the problem. It won't. At best it will postpone the observance of the problem by a few minutes or until the weather gets hotter.

Last but not least: All you folks that are using your cluster gauge as a way to determine if your changes to the cooling system have an effect - Stop it. Use an IR thermometer or, better yet, a contact thermometer. With the pre-'89 spade connectors to the cluster sender you can change the 'calibration' by unplugging the connectors and plugging them back in. ('cause you're scraping-off the green oxidation on the connectors and changing the resistance.)


As for why Porsche decided to change to 83-degrees the likely answer is 'emissions.' A cooler engine is a dirtier engine and the faster you warm it up the quicker is your exhaust cleaner.

worf928

The Bosch Hammer usually shows me 192-196 for S4s and GTs. GTSs seem to want 199. (This for 928s with no cooling issues.)

All the modern Porsches run ~210 (IIRC) unless you click sport mode, in which case the core temperature drops (over the course of minutes) to 194-196.