Porsche Enthusiasts Club Forum

My engine temperature sits at 88 degrees, just below the 90 degree mark (but never touches it). Is this acceptable? Also I noticed that after a run the cooling fans are often running but the vents in the front grille are closed. However they did open when I turned on the air con (before it failed) so they do work.

Hi

Its correct...

All the best Brett

The temp is fine.

You may find it runs a few degrees cooler with a new seal behind the thermostat. This usually degrades over time so some coolant is allowed back into block which would otherwise be diverted to the rad. Next time you change coolant (or if you drain a little fluid from rad and have car raised at front) you can get at the seal by removing the t-stat. It sits in the coolant bridge (not to be confused with o-ring on radiator side of t-stat) and when the t-stat opens it pushes against this seal and, well seals! It's a metal band with thick rubber coating and this rubber degrades so seal no longer perfect.

Getting it out of the coolant bridge is fun!

p/n 928 106 163 00. Last one I bought (will fit at next coolant change) was about £7.

This is counsel of perfection though, as you are not running too hot. Nice thing to do rather than need to do.

The workshop manual has a very useful and simple section on troubleshooting the flaps. One thing you can do to start is check that they run through a test cycle when the ignition is turned to run position, from closed to open and back to closed. Can't remember if you need to turn engine on so try both ways and see how flaps behave.

Thanks for the advice. I'll get the new gasket and also check the operation of the grille vents.

Does the thermostat housing have a gasket (between the housing and the engine) as it sounds like the seal mentioned above is inside the housing itself.

Hi Lightning

Yes the seal is behind the thermostat inside the coolant bridge. There is another o-ring on the rad side of the thermostat (if you buy a new t-stat make sure the o-ring is correct size as some of the aftermarket ones are supplied with incorrect o-ring. Purchase from Porsche or 928 International to name two ensures correct o-ring).

Thanks for the advice, I've got the seal and 0-ring from Porsche, a tenner for the two.

Is there a drain tap for draining the coolant? I'm going to need to drain some out to change these parts.

As long as front of car is raised you only need to drain the rad.

The drain plug is on driver side, accessible through big hole in spoiler. It has a very low torque (plastic plug) so will just turn out with screwdriver. You'll catch about 8L so have a washing-up bowl handy.

By coincidence I was changing coolant today and also changed that seal.

For complete coolant change you also have to remove the block drain plugs, one either side of crankcase.

So I drain the coolant out of the radiator and then replace the seals.

Do I just pour the coolant back into the expansion bottle to re fill the radiator, or is it more complicated than that? The coolant has just been changed so I'd like to save it, and put it back in.

Yes just pour it back in via expansion tank or you can bung it down rad top hose which is a bit faster but requires undoing the hose connection at coolant bridge.

The 928 system is also self-bleeding so no need to worry about air bubbles or 'burping' system. Just run it with heater full on till t-stat opens and check level (should be at seam half way up tank) after a few minutes in case you've lost any when you drained the rad.

I replaced the seals today. There was nothing left of the old thermostat gasket, except a rusty brown ring....all the rubber had gone.
The job was easy to do, but I can't see how it could make the car run cooler. Surely if the thermostat gasket has gone the engine will just take a bit longer to warm up? (as the thermostat causes the water to bypass the radiator until the engine is warm, if some water gets through it will just mean it takes a bit longer to warm up as it's going through the radiator?)

I was surprised to find my seal (believe it's original - no service record to show otherwise) in very good condition with almost all rubber still in place.

The one I replaced on previous S4 was similar condition to yours, with most of rubberised coating missing.

It is a bypass system, but my understand - which could be wrong - is that when t-stat is below operating temp it's not sealing against that ring, so water flows back to block. Above that temp the t-stat opens and pushed against the seal, so if the seal is poor some of the coolant which should circulate to rad can still flow back into the block without passing through rad resulting in high coolant temp.

The photo shows good condition of my old seal.

I was wondering, as my engine still runs at about 88 degrees on the temperature gauge, whether this is still a bit high, or is it OK?
I imagine that the thermostat must be an 87/88 degree one, although I forgot to check while it was out of the car. Can I fit an 85 degree one, or is there no point? I thought the car was supposed to run at about 85 degrees.

I think choice is between 75C t-stat and 83C, with latter specified for cars from around 1989 onwards.

In hot climates people sometimes fit the 75C in newer 928s because of the higher demands on system, but shouldn't be issue in our climate.

If you fit the 75C you should see cooler running temp. You could also add some Redline wetting agent which helps with heat transfer from coolant to air.

I think your temp is fine, but there are other causes for high temp including radiator blocked with debris etc, water pump not operating at full efficiency.

Oh I found the pic of the rear seal from my previous S4. You can see it was in the more typically poor state of an original seal (the service schedule does not dictate seal change, though the nature of 928 cooling system means it's important at least in hot climates)

Mine looked just like the picture above.

I've ordered a new thermostat from Porsche...it's only £20. The existing one was fitted in 1999 when the head gaskets were done so it won't do any harm to change it.
Porsche now only supply one type of thermostat for the S4, there used to be a pre and post 1999 version. I don't know what temperature rating it will be, but as it's from Porsche themselves I assume it will be the right one!