I bought an old aux. el. water pump. I don't know the condition...impeller turns easily but I don't know the condition...it might leak for instance.
I removed the 4 screws and the plastic housing comes off. The O- ring is old ...original ring has maybe size 38 x 2mm.
I'd need at least a new o-ring here ...not sure about the shaft seal.
To get to the shaft seal I would need to remove the impeller. But the impeller is not supposed to be removed as it is on a knurled shaft.
Anyhow with a new o-ring I could at least try to test the pumps for pressure of 1.5 -2 bar (pressure of the cooling system)

Has anyone done rebuilding of this pump?

Also the original plug is missing as you see in the picture. Is a plug available from MB and who has the part number?

Best, Martin

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Hi Martin,

Check out the link below to our site's DIY tech article on replacing the water pump. Give our MB parts specialists a call at 888-280-7799 and they'll be able to get you sorted in regards to the missing part(s).

Mercedes-Benz W126 Water Pump Replacement | 1981-1991 S-Class | Pelican Parts DIY Maintenance Article


-Dmitry

Don't even waste your time trying to fix one of those. Either bypass it or replace it. The heartache of failure simply isn't worth it. Not sure how hot you want your car, but my SDL doesn't have a working AUX pump and I don't see any reason why it should. Gets plenty hot even on the coldest days.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Martin if you decide to replace do not be tempted to buy MTC brand. Total garbage. Bite the bullet and Benz OE only on this one.

Thanks for the comments,

couldn't resist to open up the aux pump.

The replacement o-ring is a 37 x 2- confirmed

Still the pump was leaking air (tested 1 bar only)

So I pulled the impeller and the parts below.
Of course the rubber seal for the shaft is old and leaky.
All custom seals down there- You are right ...not worth trying to repair this unless you are starting an entire project.

If I have enough time once I just might give it a try.

I'd need to machine a new seal body in aluminum with new rubber o-ring seals.
Please find a picture of what I found inside after impeller removal.
I also don't understand 100% how the shaft seal is supposed to work really.
The rubber ring in the 'cup' is clear (it seals against the rotating pump shaft) but how the heck was the 'cup' sealed against the housing?
Martin

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Pump Seals in more detail


Now I have an idea how the pump seals work (sealing the rotating shaft) .
If you look at the picture/top you see that bigger ring measured 5.6 x 16 x 4.5mm (bore x OD x height). This part consists of 2 parts. The rubber boot around a white material ring. Can the while material be ceramic as it is smooth and hard (and it is like polished around the area where the cup could sit on it)
I believe this is a gliding surface for the underside of the plastic cup (material Bakelit?) to seal while cup is rotating with the impeller.
The thing is that the rubber boot's 16mm outer diameter is a bit less and does not seal very well any more against the housing (16mm bore). All the rubber is hardened and of course then seal is compromised.
I think I can find the correct o-ring (e.g. 5 x 2.5) for inside the cup (5 mm Shaft to the 9.4mm cup bore) but that boot is something else. Maybe a Teflon seal bandage around the circumference would do that job.

I was wondering before at a main water pump in my good old W109 (when it started leaking temporarily) what the inner seal was... I think I saw something similar in bigger, can't quit remember. Can someone answer this question about a sliding seal in coolant pumps. How does this work?
Best, Martin

The shaft seal you show above is a carbon/ceramic shaft seal. Extremely common in water pumps of all varieties. The piece with the white center is a ceramic material, the black "cup" you mention has a carbon face on it. The carbon rubs against the ceramic and forms a dynamic seal. These types of seals have to remain wet or they will leak. Once the ceramic is worn to the point that it is rough, game over.

Sometimes you can resurrect one of these types of seals if it isn't too far gone. On a flat surface (like a pane of glass) lay down a piece of 2000 grit sandpaper, press the carbon face against it firmly and give it 1/4 turn, and no more than that! It should knock off any high spots and allow the seal to re-seat. The pump MUST have water in it when you run it, or you can burn the seal out in a matter of seconds.

All that said- would I try to fix it? No. If it ever leaked, the motor bearings are failing sooner rather than later.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Thanks... that is exactly it.
You are absolutely correct... this is a 'wet' seal ceramic against plastic...don't see any carbon or is the entire cup a carbon piece...I guess so.
Maybe the dryness was the reason the pressure test was bad... but also the rubber seals are 'gone'.

Maybe time to say good bye.
Interesting anyhow... to play Sherlock

Martin

I had a try at repairing one of these after the one on my car went down .And i replaced it with a Valeo pump .Still running now after 5 years . Now you can bypass them , but its there for a job .If mercedes could make the engine run right without the pump in question they would have done .As the auxiliary coolant pump is in there to stop hot spots in the heater system as well as the engine block .Because the main coolant pump on the engine is not efficient to do the job on its own..

Where do you get a 'Valeo' Pump?

I have replaced seals now (use 37 x 2 for the 'head gasket' and a 12.5 x 1.8 for the ceramic ring) and the old pump seems to be fairly tight , much better than it was before,.

Not sure I could try it out until I have a better one, Valeo?

Martin

What a steaming pile of bull*****. The Aux pump is there for the sole purpose of boosting the heat output of the heater core. Read the service manual, it even tells you that. The Aux pump is simply a convenience/comfort item. With it bypassed the output from the heater is slightly less and reduces a bit at stoplights or when idling. It has NOTHING to do with cooling the engine.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

aux pump continued: I have tested the resealed aux pump (spins and is fairly tight) and installed it... seems to work...but I am not 100% sure if I connected the pins correctly as the plastic plug housing was not existing. I just plugged in the 2 pins and there are 2 options.

I guess the wheel needs to spin so the water gets thrown out to the circumference of the wheel housing (if it spins the other way must be wrong).
I tested the pump rotation direction... I left the pins in the order shown in the picture. Maybe someone can say if the orange /black wires are connected correctly??

No coolant leaks! (lucky me).


Now the Monovalve disaster: I installed one of these crap aftermarket units and I seemed to get heat for a while (maybe 10 minutes) but after that the heat went away and never came back! Cold air only. I'll start a new thread with the monovalve.

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Rebuilt aux pump works well (I am happy) and I bought a new Mercedes monovalve for $ 38. As a note never ever but the junk aftermarket monovalve!

Can someone help me with the plug at water pump- see my last picture.

Martin

Monovalve or monovalve cartridge for $38? A monovalve lists for over $400.

Sixto
83 300SD can be yours
98 E320 wagon

Careful with the aux pump. When those go south they normally fry the push button control unit.

Mine is unplugged until I can source a proper one. Its only function is to make the heater run warmer at idle.