If the magnet is the problem, would heat just be ON/OFF and not controllable? Also, I've not seen that magnets are available. Are they?

Question/ Trying to learn: If heat is controllable at low speed, wouldn't magnet be OK? Why would speed cause low heat. As I quoted earlier, mono valve innards looked OK before rebuild kit was installed.

Pat

At this point the next step must be to inspect the monovalve itself and make sure the diaphragm is not torn. If it's torn then many other solutions are moot until you replace that part. Since tearing of the rubber is so common look there now. It takes about 2 minutes to inspect it and all you need is a screwdriver.

There is no magnet in the monovalve. There is a solenoid for valve actuation. Does not sound like the monovalve is your problem since power is needed to shut off flow.

Put your hand on the in/out hoses of the monovalve. If they are both hot, monovalve is not the problem.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

How will the solenoid actuate when there is no magnet?

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

By sending electricity through a coil of wire. Isn't elecity great?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

That's a little hard to do at highway speeds.

Sounds like you rebuilt the monovalve with a kit already? The monovalve is a normally closed open/ close type valve actuated by a solenoid to control temp by cycling at different rates.

Is your coolant level ok? What is your coolant temp? Shut engine after a long drive and feel all the coolant hoses/ radiator and report back the relative temps. That will tell you if there are flow issues. Upper lower rad hose, hose in and out of the firewall are the important ones to feel.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Higher engine rpm results in higher coolant pressure at the monovalve. Either the diaphragm is allowing coolant flow to the back side (which will prevent the valve from opening) or the spring in the valve is too weak to overcome the higher coolant pressure at high rpm. Or some combination thereof.

Be mindful that the monovalve is closed electromagnetically and spring-loaded to the open position. If you don't believe that the monovalve is the problem, replace it with a piece of copper tubing and you will have more heat than you can stand. I guarantee it.

Your problem isn't electrical. It isn't airflow related. It's the monovalve.

Its still available.
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

Attached Thumbnails

 

__________________
'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

Only the $128 genuine Mercedes part is called a lifting magnet. Kinda expensive heh? Must be a translation issue. It can't be a magnet. An electro magnet yes. Plain old magnet no.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Thats what mercedes calls it.

__________________
'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

100% true.


/

there is one thing which happened to me with monovalve
it melted completely and the plunger inside of the coil stayed
in closed position in a way that spring was weak to re-position
it on lack of voltage.

it was not obvious from the outside,..it melted inside the housing.


.

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w126 500SEC gen II euro, powered by OM617 turbo stolen from 84 300SD 2.88 diff,EGR blinded
next wish/project: w114 coupe OM603 powered

The electromagnet is the coil where the monovalve, AKA lifting magnet, slots into. Monovalve "rebuild kit" itself IS the magnet.

I got new one from MB, $108 through my parts guy. Same rubber labeling as my old Bosch unit, which also ruptured years later. MB has 1 year warranty on item.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Mercedes calls it a magnet but that is technically incorrect, as I pointed out earlier. Just think, if it really is a magnet, it would stick to anything that is iron and stay in one position and not able to be moved into the open/ closed positions.

Wikis on electromagnets and solenoids:

Electromagnet - Wikipedia, the free encyclopedia

Solenoid - Wikipedia, the free encyclopedia

An electromagnet is basically a coil of wire wound around an iron core (what you are incorrectly calling a magnet, the part that has to move, to do the actuation).

This monovalve assembly is an electromagnet, or solenoid:



Monovalve iron core actuator (what Mercedes calls a magnet? which it is not):

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked