billdrah

This is my friend’s car, he is at wits end and I’m hoping for some help or insight from the knowledge base here. So these are the facts as I understand them:

Car: 1988 S4 in otherwise top-notch condition.

The problem: the coolant hose that runs from the water pump housing to the Y pipe connector forces it self loose and puking coolant ensues.

When it occurs: After the car has been driven and then parked with a hot motor, never while driving. Mind you the car does not run hot before the blow ups.

Service completed before problem started: The car went to Greg Brown for a thorough inspection. At the time the Greg said water pump and timing belt need to be done before heading across country but are fine for now. He did replace the radiator hoses, including the hose in question and fuel lines at this time along with about $8K worth of other catch up work.

The problem starts: The first time the car leaked coolant was about 1000 miles after leaving Greg’s shop, so please don't think I am implying he is culpable. The problem presented as coolant all over the front of the motor but no obvious leak point. Getting the car back to Greg is not easy for my friend requiring he basically take a day off work, and in this case figure out how to get a broken car 2+ hours north of his local. So the car went to a more geographically desirable independent shop with what is described as a strong 928 mechanic. By that I mean the my friend is told guy was factory trained by Porsche on the model, has worked on them since they were first introduced and currently maintains several 928’s in the area (North San Diego). When the car was dropped off there were in fact two other 928s in the shop, this seemed a good sign. They Diagnosed as bad WP and replaced it along with TB while in the area, thermostat, obviously new coolant and associated parts.

Second time: The car then went less than 50 miles, parked, and a short while later coolant everywhere, and this time the source is obvious. The hose described above is loose enough that when squeezing it coolant can be seen escaping the end onto the water pump housing. I am calling this the second time because while showing the mechanic this he remarks ‘that’s the same hose that was loose last time it came in.’ No one there had said this to my friend before so he just went along with TB WP as recommended by the shop last visit think the WP is the culprit. Anyway this time the part labeled at fault was the clamp, new factory clamp is installed, I assume coolant refilled, burped, and off he goes.

Third time: Again Less than 50 miles since leaving shop, same hose pops off again, same situation car parked when hot some point 30-45 minutes later dripping coolant. This time he can pull the hose and clamp off by hand. So tighten clamp, drive to shop. They all scratch their heads and conclude new hose, and new clamps all Porsche parts. My friend notices the coolant overflow cap is “hecho en mexico” and has a Behr cap put in place from Porsche.


Fourth time: Less than 50 miles from leaving shop, parked hot and same hose leaking again.

I tried to get some insight here last week posting in this thread, but no responses. To me it would seem that when the motor is hot and turned off for some reason the coolant cannot expand into the overflow tank and this clamp is the weakest link, but that’s just my guess.

Any thoughts or suggestions would be greatly appreciated? Thanks.

Tom in Austin

One thing about those Y-pipes is they rust something awful .. wonder if the end of the pipe under that hose connection is all rotted out?

BTW, Roger at one time was investigating making stainless steel replacements, but not sure what happened to that idea.

billdrah

To be clear the hose comes loose at the connection to the water pump housing not at the Y pipe.

ROG100

The system could be seeing pressure and blowing the hose off. How is the expansion cap?
IIRC where the hose goes to the water bridge the spigot has a raised surface to better clamp against.
Can you show a picture of the hose spigot at the water bridge?

billdrah

New Behr cap just installed.

I can try and get one but in the interim my friend says the flare or bell in the spigot is in good shape. I will be sure at the least it gets looked at closely. Thanks.

ROG100

So it should not come off if the clamp is tight. Something is not right. I know you said the hose was new but as it has come off so many times it may be stretched.

ROG100

It is possible but rare that the heater pipe is corroded and clogged in some way between the hose, metal pipe and expansion tank. The Y on the metal heater pipe has one branch to the expansion tank and the other from the heater matrix. You may want to remove the expansion tank and check.

billdrah

Yes the hose was new from Greg Brown and replaced again just before the last failure.

Well that's certainly something to consider.

Thanks Roger

Speedtoys

Is the metal powder coated? Or bare.

worf928

I for one would like to see a picture of this.

Absent a picture, if this 928 were here I would pressurize the system to whatever pressure the reservior cap holds and then watch that hose.

Autozone/Advance Auto/whatever will rent you a cooling system pressure tester.

The system as designed should hold no more than 14psi. Most older caps pop at ~10. That's not that much pressure. I would think that enough pressure to pop a properly-clamped hose off of an undamaged receptor would split the end-tanks from the radiator before popping the hose.

Weird problem. Let's see a picture of the area. In fact, let's see a hose-off picture of the water bridge too.

dr bob

Has the water bridge (and the nozzle inside the sliding hose...) been painted or powercoated? If so, use a little paint remover followed by some sanding as needed to get the outer finish back to bare metal.

GregBBRD

My understanding in talking to the customer, yesterday, that the problem was at the "Y" pipe that goes back to the heater and the expansion tank.

Since this is quite rare (I've never had this happen) and it continues to happen, something is obviously wrong besides the hose, the clamp, and the guy that tightens the clamp.

The client tells me that the steel pipe has the bulge at the end to retain the hose and looks to be in perfect condition (That's really rare, all by itself!), yet he can pull the hose off of the pipe one the clamps is tightened, by just pulling on the hose.....that's not right!

Tough to tell anything from afar, but the shop he is using 120 miles away is an adequate facility and quite capable of tightening a hose clamp.

worf928

Not at the water bridge as described above.

Maybe a new part? The wrong part? Not from a 928?

928 574 106 03 is what I think we're talking about. It's the same 78-95... so... strange that it's "like new" but the hose ...

The next-most obvious explanation is that the hose was mis-manufactured and is too big.

We've all see the wrong part with the right part number on the bag/sticker.

For example: At the moment it would appear that Porsche is unable to ship big o-rings for the low-pressure A/C connections that actually even look like they fit even though they have the correct part number.

WallyP

My first check would be to see if the clamp being used will actually snug/tighten on the bare Y-pipe. If it will tighten on the bare pipe, it should certainly tighten firmly when the hose is installed...

billdrah

First off let me say thanks for all the insights.

Greg you and Bob must have had a failure to communicate but the problem is at the water bridge, not the Y pipe.

Yes the unit has been powder coated. I'm told removing this or roughing up the surface is the next plan of attack in conjunction with 2 hose clamps. I guess that leaves me wondering why no problem for 1000+ miles then new hose new WP new clamps = repeated failures?

Sorry the car is at the Indy so can't get photos at this time.

This really makes me wonder, how is this hose clamp failing at such a low PSI?