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Causes of water bridge seal failure?

 
Old 01-13-2019, 04:15 AM
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Otto Mechanic
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Default Causes of water bridge seal failure?

Sort of an academic question I suppose but I'm planning to open up my intake for the third time in as many years, this time to find a leak that's filling the valley of my '85 S3 with coolant. I suspect the water bridge but I'd kind of like to understand why it would begin leaking? What might have happened to cause it? To the best of my knowledge it's never been removed, though I did disconnect and reconnect the hoses to it a few years ago. Would it just be thermal? So many heat cycles and the gasket lets go?

I'm mostly trying to figure the odds it might be something else entirely, though I can't think of much else it could be.

Thanks,
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Old 01-13-2019, 09:53 AM
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good odds that the heater valve port gasket is leaking or has loose bolts,
and or the left head block off plate could also be doing the same
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Old 01-13-2019, 10:28 AM
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My bet is on the Large "O" ring, seen that one more than the heater valve assembly or block off plates
Especially if it gets cold, the rubber has "shrinkage when cold", some of you may get that

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Old 01-13-2019, 12:59 PM
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The heater valve may be a good call anyway though Dave since it's on Dwayne's "list of things to do" during an intake refresh and I did pretty much follow that script, though I don't remember it (which isn't a big surprise for me). It's possible the valve was removed then and the bolts either weren't properly torqued or they backed out anyway. It's definitely worth checking.

The car has seen some extreme cold, it was stored in Etna Wyoming for several years, winter temps can get down to -30F sometimes. The car was always winterized but like you say, cold by itself can effect rubber.

Either way, it looks like the intake is coming off again this week. I just had it off last September for the fuel line replacement, should have done this then.
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Old 01-13-2019, 05:16 PM
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SteveG
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Look at the design and the channel the O-ring seal follows. If nothing else affects it, it is a narrow little bugger and the heat factor is significant for this small ring. They fail frequently. And when replacing, most people add a bead of gasket maker and a paper seal over that. The little fellow needs all the help he can get.
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Old 01-13-2019, 09:16 PM
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Originally Posted by SteveG View Post
Look at the design and the channel the O-ring seal follows. If nothing else affects it, it is a narrow little bugger and the heat factor is significant for this small ring. They fail frequently. And when replacing, most people add a bead of gasket maker and a paper seal over that. The little fellow needs all the help he can get.
Will do. I'm trying to assemble a list of seals and gaskets I'll need for this so I have everything on hand, anyone have recommendations for gasket makers? I have a fair assortment collected but I'm always open to specialized suggestions. As far as paper gaskets go, did you cut your own or is there a part number?

Thanks,
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Old 01-13-2019, 09:20 PM
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Question for Stan about the "block off plate"; when you say left I assume "driver's side", as in LHD? As I recall the heater valve port is on the right, so there must be a block off plate in a matching position on the left?

Thanks,
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Old 01-13-2019, 09:48 PM
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There are two water openings at the top of each head. On the front they flow to the water bridge. On the rear, the driver's side is blanked and on the passenger side the heater valve port caps the opening.

These port seals typically don't leak unless their bolts are loosened (which will happen during an intake refresh) and aren't re-tightened.

There's a large o-ring for the water bridge's connection to the block above the water pump. That o-ring, just like every other piece of rubber on the car will eventually become plastic rather than rubber due to heat cycles and exposure to oxygen. Once plasticized rubber doesn't flex and thus doesn't seal too well.

Water bridge seals (5 total) should always be replaced when the intake is off (unless they're young and the intake is off to correct the previous intake job.)
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Old 01-13-2019, 10:06 PM
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Originally Posted by worf928 View Post
There are two water openings at the top of each head. On the front they flow to the water bridge. On the rear, the driver's side is blanked and on the passenger side the heater valve port caps the opening.

These port seals typically don't leak unless their bolts are loosened (which will happen during an intake refresh) and aren't re-tightened.

There's a large o-ring for the water bridge's connection to the block above the water pump. That o-ring, just like every other piece of rubber on the car will eventually become plastic rather than rubber due to heat cycles and exposure to oxygen. Once plasticized rubber doesn't flex and thus doesn't seal too well.

Water bridge seals (5 total) should always be replaced when the intake is off (unless they're young and the intake is off to correct the previous intake job.)
Thanks Dave, I think that locates everything for me.

I'm certain I didn't remove the water bridge during the refresh, though I recall probably removing the oil filler since I have a new oil baffle I forgot to install while it was off. I'll probably correct that this time.

It's likely the heater valve was either intentionally removed or loosened because something else was perturbed during a Dwayne style intake refresh, I can't recall. If it was removed it would have been replaced to spec but may still have not been done right so I think it's worth planning on re-sealing it. I'm fairly certain I left any blanks unmolested.

I'll plan to remove and reseal the water bridge this time given the age of the sealing materials and the fact I personally exposed the car to extreme low temperatures during the 'oughties. I've begun to assemble a list of sealing materials, gaskets and rings so I appreciate all these suggestions. I live in a remote area and I'm working on a rare car, no different from the rest of us . The more ideas you folks can send me, the better prepared I'll be for the job.

Regards,
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Old 01-13-2019, 10:25 PM
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use DC111 on the fat O ring it will preserve it so it keeps on sealing
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Old 01-13-2019, 11:10 PM
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Originally Posted by Mrmerlin View Post
use DC111 on the fat O ring it will preserve it so it keeps on sealing
Thanks Stan. Somehow I knew you'd have a preference for the perfect sealant .
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Old 01-13-2019, 11:28 PM
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the heater hose on the back also has some issues where the pressed in barb separates from the base where it bolts to the head.
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Old 01-13-2019, 11:48 PM
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Originally Posted by 928sg View Post
the heater hose on the back also has some issues where the pressed in barb separates from the base where it bolts to the head.
Yup. There's an updated part that is a single piece rather than a two piece interference fit. IIRC pre-'89 have the two piece part from the factory.
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Old 01-13-2019, 11:54 PM
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Originally Posted by Mrmerlin View Post
use DC111 on the fat O ring it will preserve it so it keeps on sealing
Sometimes these engines are getting so pitted in the bore where the big O-ring sits that more aggressive action is required.

Corrosion caused from not changing the coolant or using the wrong coolant is going to be the long term problem with 928 engines.

The price difference between cheap coolant (change every two years) and Porsche coolant (change every 5 years) won't pay for the label on the head gasket set, people.



​​​​
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Old 01-14-2019, 12:47 AM
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Originally Posted by GregBBRD View Post
Corrosion caused from not changing the coolant or using the wrong coolant is going to be the long term problem with 928 engines.​​​​
Like Mark Twain once wrote: “It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so".

Don't know about anyone else, but I can say for sure that 35 years ago I had no idea coolant pH was important. In fact, I'd go so far as to say I was pretty sure it wasn't.

One of the privileges we all have, and one of the burdens, was to be among the first. There are prices to pay for that, but lets not forget the benefits. I'll never have that chance again and I wouldn't give it up for anything in the world.

PS: And let's also not forget; for a few years there, we brought terror into the hearts of the 911 faithful . Now they're all driving 928s and most don't even know it...

Last edited by Otto Mechanic; 01-14-2019 at 01:26 AM. Reason: Clarification
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