You'll know if the O ring is too thin, the housing will leak. Don't ask me how I know!!

 

I meant to say too thick, if you look at the housing there are two steps one were the T sat sits and the other were the elbow sits, if the o ring where too thick the elbow will not seat properly in the housing allowing the T Sat to move.

 

Great thread!

Bump...

 

T_Max has the problem figured out, but my fix didn't work. The car ran perfectly cool until the last mile or two of my usual 8 mile test loop when the temp slowly crept up to the old readings. I probably didn't get the thermostat seated correctly since the back of the thermostat is now deeper than the seal and it's difficult to seat it in the center of the housing.
I've ordered a GENUINE Porsche thermostat and O ring and we'll see what difference that makes.

 

Steve, if O-ring was on the thick side of the spec. it would provide more force not less. The O-ring uses the inside step on the water neck to push against the T-stat, you had it right the first time.

Here's the order as I see it:
Water neck, O-ring, T-stat than the housing.

Sterling, that would be cool, but all we really need are hard number, measurements of different, cross over pipe/ T-stat housings, T-stats, O-rings and rear seals to see if there are any dimensional differences.

 

Hi
ErnestSW,
I am no "928 expert" but as I have been recording engine operating temperatures as part of the Oil Condition report issue so the following may help

Firstly, I wonder what caused the disparity between valve cover temperatures? This could be a coolant flow restriction caused by your previously stated "O" ring breakup perhaps. I would check this out to confirm it or discard it as an "issue"!

Thermostats come in a number of types. The Porsche OE is a "progressive" type - progressive in that it will be in a constantly changing position ( between closed to fully open ) according to the heat load from the engine. In my humble terminology, "closed" means a completely cold engine!
The alloy heads and block, the oil cooler thermostat ( starts to open at 87C ) and air flow plus ambient all play a role in this. I think the role of the alloy's rapid heat transference is often forgotten too

The Porsche OEM thermostat will have the characteristics known to and specified by the original Engineers. Production tolerances on OEM supplied "O" rings etc. will have been allowed for

The thermostat will "read" coolant temperature from the engine and from the "heat sink" radiator and continuously modulate and blend the coolant flow accordingly. It will probably err on the cooler side ( under fully open at 98C ) due to the previously mentioned heat loss from the alloy engine. This means that the flow through the radiator will rarely - probably only at high ambient, restricted air flow, high load or perhaps idling with A/C on - be at its full flow capacity

This will tend to make individual engine's normal operating temperature some degrees apart - due to the "matrix" of the factors mentioned earlier

I suspect that in my car the thermostat is rarely ever fully open meaning that its rear seal will not often be completed. This can be deduced by the outlet hose to the radiator, thermostat housing ( radiator inlet side ) and the oil cooler's entry pipe temperatures

Now you can understand my reluctance to quote a "normal" temperature because of these factors. I am still taking measurements. So far the ambient temps. have ranged from -2C to 31C. The following four temperature reading points have remained very consistent
If these four readings - near the NTC and both valve covers ( same temp ) - and the front of the thermostat housing are all under/near 100C, I believe that the engine will NOT be anywhere overheating.
These readings should only be taken on a typical day at your normal operating ambient and the car having been run for about an hour or so

These engines will always seem to be "very hot" due to the heat being shed from the alloy components - not the same as in an Iron block engine. And remember our abnormal heat sink radiator's function too - this makes conceptualising difficult !!!

I hope this helps
Regards

 

Hi Doug,
Thanks for the input. Your thoughtful and considered opinions are welcome, especially in view of your objective approach.
ASSUMING that the "normal" operating temperature is approximately 187F, some cars appear to run in that area, and some cars appear to run in the 200F area. T_Max and myself, among others, have observed the higher range in our cars.
I have become very familliar with MY thermostats, neither of which is genuine Porsche. It's clear that your description of "progressive" is correct in that the thermostats are designed to MIX hot coolant from the engine with cool coolant from the radiator in order to maintain an optimal engine temperature.
It APPEARS that, in order to maintain about 187F, the hot flow from the engine needs to be completely blocked in T_Max's car and in mine and, since this is contrary to the basic design of the Porsche thermostat, it raises more questions than it answers.
I think that blocking the engine side addresses the result of the problem without understanding the problem itself.
I'm looking forward to installing a Porsche thermostat and O ring (my rear seal is a Porsche part) and seeing whether things change.

 

Ernest, if you think something is blocking the water passage ie: the disintegrated rear seal. Is it possible to back flush? Reno

 

Reno,
According to Sterling the water passages are quite large. He says you can put your finger in them. I doubt the rubber from the rear seal would cause a problem. T_Max has a brand new engine from Devek and is experiencing the same problem, as are many others. If the GENYOOWINE Porsche thermostat doesn't fix it I'm gonna get an exorcist!

 

Steve,
Ok, now I got your point regarding the O-ring, but I doubt you can get the housing sealed if the O-ring is so small that the thermostat can wander forwards and backwards
Ernest,
I am looking forwards to hear 'the end of the story' - I think (hope) the new original Thermostat will solve your problem

 

Ernest, I had my car out today and while driving with the ac on the needle stays in the middle but while in traffic the needle crept up to the top white line but never passed it. If I keep the ac off the needle always stays in the middle, in traffic or driving. Are all your test runs with the ac on or off? Now you got me losing sleep. Just kidding. reno

 

Reno,
All my tests are with the AC on recirculate which turns it on full blast AND turns the radiator fans on full blast as well.

 

Ernest,
As you wait for your Porsche T-stat, I thought I would add another variable to your deliberations. The temp differential between your 928's left and right heads concerns me. Could a weak (or clogged) fuel injector create a too lean condition in one cylinder, causing it to overheat and also be the source of your pinging? Sorry to stir the pot, but it's a slow Monday morning.
Dave

 

DG84S,
True. That difference probably cannot be overlooked.
Perhaps the problem to pursue is the pinging itself, and not the overheating per say. Why would the engine ping? I don't see how anything mechanical (stuck valve, slipped belt on one cylinder bank, stuck lifter) could cause pinging and not a rough running engine. But how could just one cylinder be pinging from overheating? If one could determine which cylinder(s) are pinging, a clue might be had.

When did the overheating start. When did the pinging start. I remember Ernest saying the engine was new, or newly rebuilt. My experience with water passages from block to heads is that it's very small in diameter. The water passages in the block and head are very large in comparison. But if that head gasket or anything is blocking what I assume to be a small hole, then.... Hmmm. Then what?
Should we be paying more attention to the water pump? I suppose that can be tested, but with a lot of work, or an ingenius method.
Free advice can be very annoying, but since we all love the 928 I hope you understand. Otherwise, it a money back guarantee.

Oh, one more thing. If injectors are suspect, then swapping, or just testing, could eliminate that as a trouble.

 

I had some subtle pinging under load in my 87S4 after putting in a set of autothority chips....even octane boost didn't help....added a adj FPR..didn't cure the problem..

Finally I pulled the injectors and had them flushed and balanced....before report came back that a couple were flowing slightly less than the others....after balancing....the pinging went away never to come back...

I suspect these two injectors were the root of the problem....It didn't run hot though...(this was a S4 AT)...

Just a SWAG....aren't the GT's known to run hotter than the S4s?.

Good luck in sorting it out..

later,
Tom
midlman@rennlist.com
87S4 AT
89GT