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Life at below 2000 RPM

1K views 6 replies 5 participants last post by  dude99 
#1 ·
Hi all,
This is a follow on to my heater problems. After replacing the mono valve kit (No torn rubber) and the thermostat, disconnecting the aux coolant pump and numerous R&Rs of associated components I am at the point that I have good heat up to the magic number 2000 RPM beyond which I lose heat. Its cold here and I am actively pissing off a lot of folks by driving keeping the RPM just below 2000 which by the way does not correspond to much speed. I have read many threads on the subject, but have not determined if anyone has figured out what is the culprit or at least a logical technical explanation of what is happening. Does paying $250+ for new complete mono valve, solenoid and all solve the problem or its the dash controller????
 
#2 ·
does your aux pump work? You say you disconnected it. If not try a working one. It made a hell of a difference in my 79 300D. Although I didn't completely loose heat above 2000rpm.
 
#3 ·
Hm. I'd test the aux pump before blindly disconnecting it. Should be easy to do, just turn the key on and go listen to it.

-J
 
#4 ·
If you used a non-Bosch OEM plunger replacement that is probably your problem. Same issue I had. Troubleshot everything under the sun and it was fine under 2k. Above 2k with neither the pump nor monovalve plugged in and the coolant flow from the engine would close the plunger and cut off the heat. Full replacement monovalve fixed it so it works perfectly with everything plugged in as intended.

If you can find an OEM plunger assembly in the junkyard that might be cheaper.

There has also been a success story noted here of removing the diaphragm from the replacement plunger and installing it on the OEM plunger if you happen to have kept it.

As an aside, if there was the same problem prior to your change of the plunger, considering that the one you removed was not torn, it was probably an aftermarket one as well.
 
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#5 ·
What you say makes perfect sense, but I could not even insert the replacement valve kit into the solenoid hole, it would go in half way and no further as though it was fatter in one end so initially I just used the rubber off of it to put on the OEM on the car (Assuming it was an OEM), but still had the same problem so I switched everything back. The diaphragm in my case was never torn to begin with, just a lot of crud on the screen which I cleaned. Funny thing is now the MV is not even connected, I had high heat all day yesterday at all RPMs, but today it got cold little after initially being hot when the car was completely warm, but the heat returned. I guess I start checking out used parts places. BTW what years and model I can use MV off of?
Thanks for your help
Ken
 
#7 ·
Something else just hit me. If you have air in the cooling system you could be getting cavitation above 2000RPM....
 
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