Auxillary water pump - help!

1979-1991 280SE, 300SE, 300SEL, 380SE, 380SEL, 380SEC, 420SE, 420SEL, 420SEC, 500SE, 500SEL, 500SEC, 560SEL, 560SEC
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CraigB
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Auxillary water pump - help!

Post by CraigB » Sat 25 Nov, 2017 3:58 pm

OK, firstly i did do a search on this and can't find it referred to on the forum. Wider searching shows where this pump seizing can set a whole car on fire from under the dash!

I have had a good run with HVAC in general and not looked into it on any of my cars, but I have dusted off Zac - the '89 560SEL - and as soon as ignition was turned on, you can hear a noise under the bonnet and pretty sure it is coming from the auxillary water pump, sitting below the monovalve. They are all close together and attached so touching any of them you feel the vibration. It remains the same regardless of what buttons you push and also the interior fan is not working.

So just checking before i start digging too much, what triggers the operation of that aux pump? I tried my gen 1 500sec and while I only ran it for a few minutes, whether i had it on full heater setting or A/c (that was blowing nice and cold) - I couldn't hear or feel any movement in the pump. So that could be stuffed? Logically, I would have thought when you have the heater on at least, that the pump would be going, but that could be very silent in operation. This could be operating as it should be ie. ignition on and it runs, but i am getting an early warning that it is about to crap itself.

Anyway, just thought i would put it out there and see if anybody had experience with this.
Craig Baulderstone
Lurch
280s's
280SE3.5
280SL
350SL
500SEC's
560SEL's

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AMG
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Re: Auxillary water pump - help!

Post by AMG » Tue 28 Nov, 2017 12:28 pm

Craig,

The only HVAC issues I ever had in Schultz were the drains from the heater box, which I removed and replaced with PE tube and the 'porcupine' blower motor controller/resistor on the blower motor, which made the automatic fan thing go funny - it can stop the fan working if it's stuffed, if I recall correctly.

Other than that, never had an issue and never had any problem with the pump - but then again I am struggling to remember whether I had a duovalve or monovalve. Pretty sure it was a monoovalve behind the false firewall, but also cannot remember any electric auxillary pump being there. I thought it might have been nearer to the header tank? I'm not so sure now I come to think of it. I'd have to go check the EPC.
Insofar as fire is concerned, I think the pump is fused - I'd have a hard time believing that a siezed pump wouldn't blow a fuse. But you learn something new every day!

I know the 124 has a duovalve and the pump is down on the chassis rail below the header tank, and in the 107 & 201 it's a monovalve on the firewall and vacuum operated, but that's no use to you for your 126039.

Let me know if you need a schematic or something - I'll email you a PDF.

Honestly cannot remember mate. sorry. Probably didn't help at all.
Current:
1987 560SL 4sp. auto Signalrot "Stella"
1987 190E 2.3-16 5sp. man. Blauschwarz "Hermann"
1992 300CE-24 6sp. man. Perlblau / Iceblau "Gretel"
1992 Range Rover Vogue SE 4sp auto Ardenne Green "Oswald"
2012 Renault Sport Megane RS265 Trophy 8:08 6 sp. man. Liquid Yellow "Jean Rédélé"
Previous:
1986 560SEL Anthracitgrau "Schultz" - In Mercedes Heaven
1987 190E 2.6 4sp. auto Signalrot "Sabine" - which now resides/owns Andrew M's Garage
1972 350SLC Astralsilber "Lurch" - now in the loving care of Craig B
1989 2.5-16 Blauschwarz 4sp. auto (parted) formerly owned by Derek/Hasan.

CraigB
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Re: Auxillary water pump - help!

Post by CraigB » Tue 28 Nov, 2017 12:56 pm

Thanks Joe - the pump is under the black box that sits in the middle behind the false firewall - short hose straight to the monovalve. Quite well hidden... great for repairs! Regarding the fires, I think it was benzworld i saw and I think it said later cars are fused or had protection. Someone sells fuse kits though for early cars. Were photos of the boards in the climate control unit all black.

Reading the story of this guys car fire, complete with pics of it basically gutted - and i think he was more upset that he didn't have time or remember to get his Glock out of the glovebox! Yes it was the US. But everyone was raving on about fire extinguishers and carrying them, which i agree, but it sounds like it started with a smell and the guy pulled over, and eventually somone with an extinguisher came by etc........nobody mentioned number one thing to do that probably would have saved the car disconnect the battery. I had that drummed into me doing fire rescue with CFS over the years - any car accident first thing is to get to the battery any way you can.

It sounds like, that apart from the monovalve the system is too reliable and nobody knows how it runs. I will hunt down a spare pump i think and just plug it in and see how noisy that is. I'm thinking that most likely the pump should be running but there is a bearing or something in mine gone and hence why i am hearing it now. Nice that the car is giving me early warnings of problems! The fan not running is a bit confusing but i also have a spare control box and will swap that in and see what happens.
Craig Baulderstone
Lurch
280s's
280SE3.5
280SL
350SL
500SEC's
560SEL's

CraigB
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Posts: 4808
Joined: Thu 23 Jun, 2005 2:18 pm
Model you own: I own multiple different models
Location: Hawthorndene (Adelaide)

Re: Auxillary water pump - help!

Post by CraigB » Tue 28 Nov, 2017 1:34 pm

Found the answer! I have had the "MB Technical Companion" by MB Club of America forever, but it never seems to answer the problems i have. That all changed today with an excellent breakdown of the CC system. "A small electric pump in the engine compartment circulates a uniform flow of coolant through the heat exchanger at low engine speeds. The pump is switched on by the electronic control unit whenever the footwell nozzles are open (heat mode). So it shouldn't be on all the time and I will swap in one of my spare control units which will no doubt solve the fan problem too. These cars really need to be used don't they.
Craig Baulderstone
Lurch
280s's
280SE3.5
280SL
350SL
500SEC's
560SEL's

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