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1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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1987 300SDL, 2011 E350
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15 Posts
ECS to the rescue?

Hi folks;
Thanks so much for the tip with the ECS tuning Genuine Benz valve insert. I have mine on order now and will report back with what I will find. The Benz dealer in Willow Grove PA had no idea that you could buy only the insert. Their only option was ordering the whole valve at 600USD.

https://www.ecstuning.com/b-genuine-mercedes-benz-parts/mono-valve-repair-kit/0008350644/

This is the last attempt with this design. If all of this playing around with the correct spring in the insert does not work then I will install a W124 valve. That one is better by design as the plunger needs to push close against the flow of coolant instead of with the coolant (the suction of the aux pump and engine water pump acerbates the erratic and incorrect closing of the valve).

All the best,
Ralf
 

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1987 300SDL, 2011 E350
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Success at last

Hi folks;
Thanks so much for the tip with the ECS tuning Genuine Benz valve insert. I have mine on order now and will report back with what I will find. The Benz dealer in Willow Grove PA had no idea that you could buy only the insert. Their only option was ordering the whole valve at 600USD.

https://www.ecstuning.com/b-genuine-mercedes-benz-parts/mono-valve-repair-kit/0008350644/

This is the last attempt with this design. If all of this playing around with the correct spring in the insert does not work then I will install a W124 valve. That one is better by design as the plunger needs to push close against the flow of coolant instead of with the coolant (the suction of the aux pump and engine water pump acerbates the erratic and incorrect closing of the valve).

All the best,
Ralf
I put in the genuine Benz mono valve insert and the heat comes on and stays on. The temp controller now works great as well. Awesome!
 

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1989 W124 260E Saloon. M103 lump.
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1,618 Posts
Thank god for that .But a leason well learnt for other members, that will have to go down this path sooner or later in the cars life timeThank yoiu all ..
 

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Hi, I was having the same problem on my 500SEC. The diaphragm inside the monovalve was torn. I've bought the MTC replacement from Amazon for 14$ althought the reviews for their producut were terrible. Ofcourse that their product did not work :) but I took the diaphragm and put it on the OEM assembly. Now it works perfectly and it is very responsive to the temp knob changes. So in the end I can say that I'm happy I spent only 14$ and solved the issue.
 

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1987 300SDL, 2011 E350
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This problem has driven me bunkers too. I made a video of the many things that you ought to check (and yes, it can be the mono valve depending on what you replaced it with).
Make sure you use the genuine mono valve for starters. Then make sure the little aux water pump is not stuck and fried your controller. Then check your inner cabin temp sensor blower motor. Finally, make sure your climate controller is the correct one and that it works. One item that must operate too is the AC compressor and system (the defroster function acts up otherwise).
 

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Canada cruiser

It would be a perfect scenario to have a T fitting with bleeder valve at the return hose from the heater core, as it is positioned at least as high the expansion tank.Unfortunately we have that monovalve and it's connections in the way.All I know for sure is if that bottom hose wont get similarly as hot as the top radiator hose,you may get heat,but it wont be anything like you will feel when all is well.I have done quite a few different makes of vehicles.This is true of all of them.The hardest car to get air pockets out of has to be a VW cabrio. Probably the easiest is a Ford fusion.Sometimes geographical location helps.I have a friend in North Jersey who lives up in a very hilly area, the driveway entrance to his garage is probably 30 degrees incline and all we do is pour in as much coolant as the expansion tank will take.Run the car.Wait for the needle to move.Turn the defrost on full blast.Top up after about 20 min.Put the cap on the reservoir,and go.
Love Canada.Furguson lake near Calabogie is blissful.
 

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know that if the acc controller is putting out ground cycles to much it will cause you to have less heat it should only ground the mono valve once every five seconds and if the aux pump is not working it will do the same. I'm working on a 350sdl with no heat at all , replaceed the insert in the monovalve and the thermostat (which it did need) but still no heat lol told my customer what the valve cost and i think its getting warm enough for them to wait till fall lol
 
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