I did a search for coolant leaks and expansion tank so as not to repost but didn't find anything quite like this.

I've got a massive coolant leak. There is a trail of tears in the parking ramp from out of sight to my current parking place. There is an ever expanding pool of coolant on the ground five minutes after I parked and there is coolant visibly *draining* not dripping from under the car...I would call it a hemorhage. But here's the thing that makes me say hmmm.

The expansion tank is full and has remained consistently full all afternoon even as the 928 cooled. However, I do know I have a leak because in October, I filled it after a coolant light came on and the expansion tank was bone dry. It did not leak noticeably over the winter in hibernation, although there was some residual anti-freeze on a spot under the car. Tonight, I'll get the airbox off and examine where it might be leaking because I suspect it is the hot water heater valve hose to the heater core (that general location) and the air box has to be removed to see it. Gulp. Hopefully not a head gasket.

Edit: temp just over 1/4 in 15 minutes of driving. No rapid temp increase. No coolant light today.

Very obliged to anyone who can help me on this stumper mystery.

I have a 1987 928S4 auto US version.

 

It'll help to know where the leak is hitting the ground...under the airbox...front of engine, somewhere else?

 

I would say under the airbox.

 

Try a leakdown on the cap....Also, take a look behind/under the relay panel and see if there is any accumulation there.

 

If the leak is under the airbox it is most likely one of the 2 short hoses that lead to/from the heater control valve.

A very common failure and a cheap and easy fix.

 

I have a similar question about coolant leak..............
I noticed a small hose just hanging down passenger side, maybe just in front of the airbox to the side of the RAD fill cap. Midway down the engine.

I thought this was some sort of overflow hose, so if the RAD was overfilled and the EXP tank was full, if there was too much pressure it would just overflow out of this small hose?

I only thought this because I had just topped the RAD and overflow tank, then drove the car (I might have even gunned it a few times ). When I got back to the drive, I saw the coolant streaming out of that small hose.

It has not done this since, so I am assuming that was the case..........

So is that small hose as described a exit strategy if the RAD and overflow are full, or is that hose supposed to actually go somewhere.............

Sorry to hijack the thread, but it just made me think of it.

 

if you find that the heater control valve is leaking make sure to replace the short hose that connects it to the head as well, these are the highest failure points in the car besides the top of the rad on the pass side

 

What Stan said about the hoses, plus there are a few others in the area there that deserve similar attention. The hoses between the block and the heater valve, the heater valve and the core, the core and the reservoir, the reservoir and the metal connecting pipe (this ones a chore..), and the one from the connecting pipe to the water manifold, the reservoir vent hoses, plus the pressure switch. These all deserve replacement every once in a while due to age and heat damage. That pretty much leaves just a couple vents and the two big hoses in front to the radiator. Replace the cap too. A leak from "under the airbox" could be almost any of those that connect to the back of the block, the heater core or the reservoir itself. Th ereservoirs have been known to fail too, if that helps.

Many parts places will loan you a pressure tester for the system that will let you pump up the system while it's still cold. The pump will also test the cap.

 

Thanks, Guys. I will check this out. Much experience and knowledge as always. I will report back.

 

I will check this. If there is accumulation behind the relay panel, is it possible for it to cause a mildew odor or should I be looking at the drain hole for the condenser? Now I'm the one hijacking my own thread.

I'm going to dig into this either tomorrow evening or definitely over the weekend. Thanks again.

 

There's a small valve just outside of the resevoir inline in the hose exiting right (as your standing on the passenger side looking at the resevoir tank)...we have found three of these leaking in some fashion on cars inspected....

On mine, I chased around this leak to a small pooling behind the fuse panel on the passenger footwell to having it trace down edges and sharp things six - eight inches on the bottom rail of the passenger door.....replaced it and leaks and drips went away....

 

I did not have equipment available to do a leak down on the cap, but I did run the engine to operating temperature and attempt to chase leaks down. They appear to be coming from lines entering to or exiting from the coolant tank. The reason I believe this is that there are tell tale signs of wetness inside the engine compartment seemingly dripping/draining from under the coolant tank. This wetness is following the subframe and steel lines (fuel lines? oil cooler lines?) on the passenger side of the car and dripping down to the ground from there.

I removed the two bolts holding the coolant tank in place and disconnected the small entry hoses (2). There is a larger hose connected to the underside of the tank that is a real PIA. My goal is to disconnect the tank, inspect the tank, and inspect that lower hose, which I suspect is the culprit. Any tips for how to get at this?

 

That lower hose is in fact a PITA to change. Knowing what I know now and considering your situation, I'd consider replacing the reservoir bottle. That makes the lower hose change a LOT easier as part of the process. The old reservoirs do have a tendency to crack with age (yours is officially old enough to drink...) and the hoses are likely the originals too. The bottle is a chore to change but it may be less aggarvation than changing the hose underneath without at least loosening the bottle. The new pretty white resertvoir will eliminat one of the underhood items that prominently display the age of the car.

My too sense.

 

if your going to change or remove the coolant bottle, all that you have to do is remove the top (small 2 hoses ).
Then looking carefully, you will see that there is a bigger hose that comes off the bottom, instead of trying to remove the hose from the bottom of the tank, just remove the other end of the hose from the hard metal line.
This is still a PITA but a bit less of one, then before you install the new tank refit the new tank with a new hose and orient the clamp so it can be retightend from the bottom .
While your at it now is a good time to replace the windshield washer fill spout, since this also needs removal and thus removal of the right front fenderliner, you can also check your 3 way union for cracks (emissions connection under the fender) and remove the metal ring in the new fill spout by dipping the end into some boiling water it simply slides out.

 

Dr. Bob,

You are correct sir. The hose is a PITA. It is 92810632301, if I am correct about this. I'll be replacing that hose, the 75' thermostat and ring, the reservoir, and the cap. And, BTW, the coolant reservoir was, in fact, cracked. Amazing-- I wonder if it was the only culprit because *a lot* of coolant was coming out. It seems like such a small little hairline crack. I think the hose was bad, too.

I checked back behind the relay panel as best as I could get to it, did not smell antifreeze, did not feel anything wet. Seems to be limited to the engine compartment and draining down along the subframe.

I cut the PITA hose out and pulled it off the Y-pipe. The PO used green stuff. Bad PO. Very bad PO. When I do the T-Stat change out and reservoir replacement, I will search the archives for flushing alternatives. I did it before in my OB previous to the S4, so it should be straightforward. Took me forever to find the block plugs from the orientation in the factory volumes.

More later and thanks again for your help.