Dwayne

For a long time, we've had a coolant leak on Idaho at the thermostat housing mating surface with the head on the passenger side. Coolant would pool in the block casting and it would insidiously follow the seam between the block and head all the way to the rear of the engine and drip down into the valley and exit out the rear drain port leaving me scratching my head as to how a leak at the front of the engine produced drips on the ground at the rear of the engine. This was especially pronounced when parked on an incline. I replaced the red rubber gaskets 3 times on Idaho to address this leak. Twice, I replaced the red gasket with the intake still installed and once when I had the intake off. Same result.

Then one day (recently) some good soul here posted a pic of this bulletin on someone's thread about coolant leaks:


Although mine is not an '89, it was experiencing the same symptoms. So I bought the flat gaskets (the same gaskets that go on the rear water ports on the heads). Then I proceeded to remove the intake and oil filler neck to get to the water bridge and fix it properly. After installing the additional gaskets and putting it all back together, the leak has disappeared!! This repair worked wonderfully and was completed in one day - including the intake removal and re-install.

Anyway, just wanted to share for others that might be experiencing the same problem and wanted to thank that "someone" that posted this tech bulletin in the first place - THANK YOU!!

Hilton

You're welcome

Are the heads on your '88 original to the car?

Its not uncommon on 87/88's for the heads to crack around the head bolts due to the pressure, and too-thin material around them. For '89 heads onwards Porsche thickened the bosses to strengthen them, and updated the heads casting revision number to R2.

I figured posting it so it showed up in searches would be useful, glad it helped.. although I've yet to find anyone else with another engine in this range. My '89 left the factory in Oct '88.

jacal128

Dwayne, I am redoing the top end of my motor, 86 5.0, I have two of these gaskets. I haven't had the car running since I bought it so I don't know about any leaks, do you think it might be worth while to add these gaskets while putting back it back together? Also the car ran when I bought it, just decided too many things wrong from the PO to drive without repairing so I took it apart the day after I bought it. Thanks Jack

Dwayne

That was YOU??!! Many, Many THANKS, Hilton!!!

I can't tell you how nice it is to have this pesky leak fixed. I thought I was going to have to resort to sealant of some sort and then I came across your post with the bulletin. When I couldn't find your post again, I searched through all the tech bulletins I got on my Jim Morehouse CD and found the bulletin. THANKS so much for posting the bulletin!

I am certain the heads are original. Idaho only had 22K miles on it when we acquired it two years ago and I have a complete set of service records that came with it. When I took the intake off, it looked like it was all original underneath and the intake appeared to have never been taken off before either. THANKS again!

Dwayne

Hello Jack,
Having just completed this repair and seeing the result, I would say "yes", install the extra flat gasket along with the round silicone gasket for additional peace of mind. They are inexpensive and there does not seem to be a down side. I don't know for sure if this problem is pervasive but I suspect it's not. On the 32V cars my wife and I own, this is the only one that had this problem. Personally, I will probably stick with the single recommended gasket on the others but that's only because I enjoy working on and fixing these cars and would have no problem taking it apart again to fix a problem like this. I'm just glad there is a simple fix! THANKS for the question!

Hilton

Hmm, curious that it leaked - I guess maybe a conjunction of tolerance differences on the water bridge base and the heads can produce the same issue on other model years? Good to know, although it seems to be a very uncommon issue. Like you say, the gaskets are thankfully only a couple of dollars each.

For the sake of others, the other thread Dwayne mentioned was this one, and covers the other source of water bridge leakage, the large o-ring.

https://rennlist.com/forums/928-foru...e-leaking.html

Glenn M

Hilton and Dwayne,
This is great, going to add them on my intake R&R on the 88.

Cheers

G Man

Dwayne, where is the write-up and detailed pics we are so used to seeing from you! This isn't like you. Glad you found the leak.

Dwayne

HA HA! I'm a slacker!

Would you believe a dog ate all my pictures?? That excuse never really worked for me in school either!

Ed Scherer

Well, I'll be damned... I just took off my thermostat housing (water bridge) to fix a leak similar to the one described by Dwayne in post #1 (coolant pooled right under the thermostat area and then dripped down in various places, pooled on the belly pan, and then dripped out when I parked on inclines). This is on a '90 S4.

And... I've already got the double gaskets. But still leaky. Unfortunately, I don't have the replacement gaskets on hand, but will obtain them ASAP.

Interesting, though, that even with the double gasketing (the usual 928.106.227.00 along with the Technical Bulletin-specified 928.106.107.00), I still developed a leak. Actually, based on a quick inspection, I actually think it was leaking at the big o-ring, not at the double gaskets.

FWIW, I saw no evidence of recent replacement (and I know the housing hadn't been off in the 11 years I've had the car), so perhaps these were installed during production.

Regardless, thanks, Dwayne (I'm using your writeup for this job, too: great, as always!), and thanks, too, Hilton, for pointing this out back in December. Hadn't I come across these posts, I wouldn't have known what the heck was going on with these double gaskets.

borland

On my 90' S4, I did not install the extra gaskets. Just the o-rings shown in the PET, 928.106.227.00.

These coolant system O-rings should not be installed dry. I pre-coated mine with silicone grease (plumbers grease) before assembly. No leaks.

Ed Scherer

Did your car originally (to the best of your knowledge) have the gaskets like mine (#392, BTW) might have?

I'm wondering if the Tech. Bulletin only mentions the affected cars (by engine number) because after that, they started installing the extra gaskets at the factory. And then eventually tighted up manufacturing tolerances so they weren't needed anymore (in which case it would be interesting to know when that was).

Seems like people who service lots of these cars would have a handle on this.

Is that the same stuff you use on spark plug boots, etc.? (I happen to have that on hand). I've got a bunch of pipe lube for gasketed PVC pipes, too.

Thanks for the tips.

supercedar

How often did you add coolant when this leak was happening? I add about 1 pint every 600-1,000 miles. I will have to watch for this.

I have a 1988 with 145,000. My previous owner treated it right. My last 928 was a 1978 5 speed with lots of problems. That was back in 1980.

Thanks for all the great reading on this site.
Thomas

Ed Scherer

Probably about that much. I didn't track it that closely, knowing that I was just going to hunt it down and fix it within a few months.

borland

On my 90' S4, the factory installed just one set of gaskets.

No, don't use dielectric grease, however it may have similar properties. You can find silicone grease (plumber's grease) at any hardware store like Home Depot. But also at automotive places like Napa.

In plumbing, its used for lubricating rubber gaskets. This is not the same product as plumber's puddy.

http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053