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  #16  
Old 09-11-2003, 11:12 AM
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Location: Plano, TX
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I'm pretty certain this test convicts the pump. If you have DVM, check the ohms on the pump. I forget the correct value, but if you get a small number, perhaps 1-2 ohms, that's your problem for sure.

I've always thought that pump was pretty darn steep for a small electric motor and some plastic. Never seen it for less than $99. Since it does not get too cold down here in Dallas I just let it go, never really missed it.

I can't comment on the 126 chassis, so far I've only suffered through ownership of 123, 124, and 210 chassis cars If I was a betting man, I'd say a shorted aux water pump damages the PBU on a 126. Both the 126 and 123 were designed in about the same timeframe, so I'd expect similar behavior. When they did the 124 ~10 years later the designers had learned the PBU needed protection from the water pump.

Where did they hide the pump on the 126? On 123 & 124 cars it's pretty much open the hood and unplug it. One minute of work, one minute to wash your hands...

Feel free to mail down some Pacific Northwest micro-brew!

- JimY
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  #17  
Old 09-11-2003, 01:12 PM
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Location: franklin,mass
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JimY, the aux pump is between the wall of the engine conpartment and the fire wall, right beside the mono valve. You can just bearly see it under two hoses. The wall towards the motor has 4 screws that will alow you to gain enough run to remove the aux water pump. I can not see the wiring for the pump, as I would like to test it, but It looks very old, so I will have to remove it to test it. steve
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  #18  
Old 09-11-2003, 01:38 PM
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Location: Seattle
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On the 126, can you pull the fuse for the AUX water pump instead of unplugging it? May be easier if the wires are buried. May also disable other components too though. If they are Climate Control related components, this may or may not confuse this as a t-shoot step.

Pump is expensive, yes, but all in all, $100 to $140 is not bad for an electric hot h2o pump which has lasted me (eruh, the car -- I bought it used) 167k miles and 17 years.
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  #19  
Old 09-11-2003, 01:42 PM
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d2bernhard. What does T-shoot step mean? steve
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  #20  
Old 09-11-2003, 04:22 PM
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Sorry! T-shoot = Troubleshooting
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  #21  
Old 09-11-2003, 08:37 PM
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thanx, i'm still learning steve
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  #22  
Old 09-13-2003, 01:34 AM
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Disconnected a 2 piece "connector" on a harness that is located right next to the monovalve but is headed towards that aux water pump...it looks pretty easy to find... ( looking at the picture was helpful --see below -- seems to be the harness that I disconnected!)

Needless to say that did NOT solve the problem, but what did was a monovalve repair kit. This on teh higher mileage 300SD. In all fairness, this car had the problem of "continous heat" and not the intermittent heat.

The other car has more of that intermittent problem so I will try to disconnect the aux pump on that one and report back my findings.

I should have disconnect this thing a long time ago as we barely need heat in California. Here's a good picture from fastlane:

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Last edited by 300sd2000; 09-13-2003 at 01:39 AM.
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  #23  
Old 09-14-2003, 08:43 PM
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300sd2000 what a great picture, have you figured out what turns this pump on and off. I still can't seem to find the connector on mine. I am sure I will be doing a mono valve repair this week just to start, see if I can get sum heat out of Big Blue, my 300sd steve
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  #24  
Old 09-15-2003, 04:23 AM
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thank fastlane for the picture...I just linked to their existing picture.....as for the location, I found mine buried right next to the monovalve. It is a detachable connector just hanging loose in between battery and monovalve on my car.
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  #25  
Old 09-17-2003, 09:45 PM
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Here is my update:
Weather is cooler and heat is on all the time in the morning on the way to work. I am experiencing the hot air blasts -- even when moving steady. Not just after sitting at a light. The system then overcompensates with cool air and higher fan speed. It seems to need the pump in conjunction with the monovalve to keep the heater core temp happy.

On a side note, my AC seems to have grenaded. It stalled the car at idle trying to engage, and now makes a horrendous noise. I keep it on EC until I can get it looked at.
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  #26  
Old 10-15-2003, 09:03 PM
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"If you have DVM, check the ohms on the pump. I forget the correct value, but if you get a small number, perhaps 1-2 ohms, that's your problem for sure."

I am a novice at electrical testing. Could someone please explain what the above means? Waht settings do I use on my multimeter, etc.?
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  #27  
Old 10-16-2003, 12:07 AM
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Just to add a little confusion, I went through an intermittent stage of getting unwanted hot air sporadically; had one episode last spring, then a few since, and finally full-time unwanted hot air last week. Replacing the monovalve fixed it nicely.
The solenoid will indeed move even if the valve has failed; what goes is the rubber diaphragm that controls water flow. When it's torn, there's flow through to the heater core regardless of solenoid position. It's a cheap and easy job.
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  #28  
Old 10-16-2003, 01:44 AM
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Thanks! I was kinda thinking this too, but have 0 experience with these.

This is not the same monovalve as on the W124 (easy but not as cheap). Can anyone corroborate this diagnosis?
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  #29  
Old 10-16-2003, 01:59 AM
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On the 124 there is no rubber diaphragm. The solenoid works direct over the metal valve that blocks the hot water flow. Due the very high pressure inside the system, a rubber diaphragm seems to be not strong enough to block hot water flow. Wich diagnose are you asking for?
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  #30  
Old 10-16-2003, 02:03 AM
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Could my problem be a monovalve problem? Or do I need to look at the panel at this point?

(the aux pump runs, and seems to be fine.)
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