leaking auxiliary coolant pump

[Dash01]

Aux. coolant pump (under the heater valve, driver's side firewall) is leaking, bigtime.

The leak seems to be from the underside of the pump, perhaps from a small rectangular hole on the bottom.

Is this a common failure point?

Can this pump be rebuilt?

Correct procedure?

[drice]

Yes, it's a common failure. No, it can't be rebuilt. It's a simple R&R for about $100, as I recall.

[Kalevera]

I TOOK MY OLD ONE APART AND I'M NOT SURE wHY YOU COULDN'T REBUILD IT. BUT EASIER JUST To BUY A NEW ONE, and prolly more reliable.

SORRY FOR THE CAPS....my keyboard is messed up.

best, whit

[Dash01]

I assume the pump itself is still working, but just leaks. How did you get yours apart? What sort of internal gaskets or seals does it have? Seems to me, this might not be too difficult. Please advise, and thanks.

[Kalevera]

Hi Dash.

Sorry about before, I'd dropped a glass of milk into my keyboard and had to take it apart...not fun.

My old Aux pump started to go in December. It was actually working just fine until I snapped the coolant return line (on a 535 it runs up to the expansion tank from the radiator). In the process of replacing that, I had to lift up on the heater valve, which is bolted onto the aux water pump. Once I'd reinstalled everything for the return line, I had a very slight leak at the lowest point on the pump (when mounted) by one of the bolts that holds it together.

I pulled mine out in the process of rebuilding the cooling system altogether (it was time).

Of course, the motor is/was fine. German motors are hard to kill...it's the gear trains or other electrics that always go bad first. The old one was an OEM BMW unit with no other markings besides "BMW" and a part number on it. The new one from BMA is manufactured by Hella. The only difference I noted between the two was the existence of a vent or hole (sounds like what you have on yours) on the side of the unit.

In pulling my old one apart: it's very easy, just remove the four long screws that hold the top onto the motor. There are no real gaskets in the unit, and it is comprised of a very simple plastic impeller.

These leak because the plastic gets old and brittle, then cracks or shatters. After taking mine apart, I would recommend replacing it. The plastic impeller on my old one was on it's way out as it had a crack through the middle of it that would have eventually broken the part in two (although there was no indication in the unit's performance that it was about to go).

Mine was leaking at the seam between the impeller housing and the motor housing. If I really wanted to save money, I would've just used some Hylomar between the two flanges and put it back together. But I probably would've had to do the job again in a few months, and it's not a fun job to do (gotta drain, at least partially, the coolant...as you probably know).

These days, I like to do things the right way the first time around. In my book, just replacing the part at $100 is a lot easier than having to worry about it failing again, and the potentially disasterous and inconvenient scenarios that accompany that situation, in the near future.

Best, whit

[Dash01]

I took the pump apart. The clear plastic cup that covers the impeller has a hairline crack along the edge, so coolant leaks out of it.

Seems a pity to spend ~$100-120 on this small piece of plastic.

JB Weld? Marine grade epoxy? Other ideas?

[Kalevera]

Up to you man, but I'd just replace it.

If it cracked once...when's it going to crack again?

[shogun]

If you want to save money, just remove it. Does not matter so much. You will get less hot water into the cabin when the car runs on idle, that is all. Just install a piece of hose there. I know of some people short of money, which have even eliminated the heater valves and just installed a plumbing valve and they just adjust it manually.
Not the most high tech repair, but it works.
I replaced my heater valves and the out of order aux pump 3 months ago, after they worked for 17 years without a problem. If you invest now 120 $ or so for a new pump, it will last longer than the whole car probably will.

[DueyT]

I took the pump apart. The clear plastic cup that covers the impeller has a hairline crack along the edge, so coolant leaks out of it.

Seems a pity to spend ~$100-120 on this small piece of plastic.

JB Weld? Marine grade epoxy? Other ideas?Dash, if you want to save some money, you can have my old one for shipping plus whatever you want to add on... The input fitting broke off and I got a new pump from Patrick at BMA for $105, IIRC. I just took my old one apart and confirmed that the clear (amber) plastic cup is not cracked at all...

I could ship the whole pump or just the little plastic cup.

Just so you know what broke, here's a pic of the pump...the horizontal inlet fitting should have four ribs like the vertical output fitting...it sheared off at the first rib...
http://www.bimmer.info/bmw/Duey/BMW%20E34%20aux%20pump%20wiring.jpg

[Dash01]

Special thanks to Duey and Shogun for their insight and help.

While awaiting the pump to get here from Duey, I decided to try Shogun's suggestion. As it happens, the hose that normally feeds the aux water pump is plenty long to just clamp directly to the solenoid intake manifold, totally bypassing the aux pump. So, cabin and defrost heat are restored, albeit without as much coolant flow as would be with the inline aux. pump. When Duey's pump gets here, I'll install it. Thanks, Duey!

I wish I'd known Shogun's bypass procedure when doing roadside repairs on Wednesday. Anyway, it's a handy procedure to keep in mind if your aux pump leaks or quits. To get back on the road, I plugged all three hoses using Majic Marker felt pens, borrowed from a roadside store near where the car started leaking. Very colorful. :p


If you want to save money, just remove it. Does not matter so much. You will get less hot water into the cabin when the car runs on idle, that is all. Just install a piece of hose there. I know of some people short of money, which have even eliminated the heater valves and just installed a plumbing valve and they just adjust it manually.
Not the most high tech repair, but it works.
I replaced my heater valves and the out of order aux pump 3 months ago, after they worked for 17 years without a problem. If you invest now 120 $ or so for a new pump, it will last longer than the whole car probably will.

[DueyT]

Dash, unfortunately when my pump sheared the input flange, it was -15*C outside (~-23F) and I was in no mood to try sticking fingers, magic markers, cigarette lighters, etc... into my hoses! :D Good that things are working out while the little beastie goes into the mail!

Cheers,
Duey

[Dash01]

My situation was a bit more benign, as weather was sunny and ~55 degrees. The little bugger (aux pump) quit while waiting in line at the Blaine border crossing into Canada, south of Vancouver. At first, I was looking for a broomstick to swipe, cut, and plug the hoses. Then spotted some Majic Markers at the tourist info center, which the nice folks there gave me, prolly just to get rid of me. Works!

[black_bird_blue]

I had exactly the same problem when gooning around at a small sprint track here in the UK; after a particularly stylish (although slower than the previous) run there was a heroic "foop" as I crossed the line; the pump had popped and was gushing coolant out of the rectangular hole. I topped up the car and limped a few miles away before calling the RAC (roadside assist). He neatly bypassed the offending item and I bought a new pump for £40 a couple of weeks later from the dealers. Utterly painless to fit, never given it a second thought since.

I too hate bodging because you always end up doing the job again before long.

Damian

[Brett619310]

My situation was a bit more benign, as weather was sunny and ~55 degrees. The little bugger (aux pump) quit while waiting in line at the Blaine border crossing into Canada, south of Vancouver. At first, I was looking for a broomstick to swipe, cut, and plug the hoses. Then spotted some Majic Markers at the tourist info center, which the nice folks there gave me, prolly just to get rid of me. Works!

Dash - do you live in Whatcom county by any chance? My parents moved to Bellingham recently and they are handing down their '93 525i to me. I've been to that border crossing several times.

[uscharalph]

Where exactly was this leak creating a pudlle? I was thinking my heater core had a leak but I've started reading about the aux pump. Did this problem create steam / fog on the driver's side windshield?

[Kalevera]

As the heater core is located inside the passenger compartment, behind the radio/deep in the center of the dash, any leaks will either go down the drain and onto the pavement or it'll end up on you or your passengers if it gets blown into the ducts.

best, whit

[uscharalph]

What I'm trying to get a feel for is if it's the heater core or the aux water pump that's leaking. Hopefully it's the pump.