tried to fix monovalve, broke car instead
 

okay, okay... thats an exaggeration. but i tried to inspect and r&r my monovalve - the part with the torn diaphragm and all. it turned into a minor disaster. first, all the coolant drained out onto the pavement when i opened it up. two, i couldnt get the valve out of the housing. it was completely stuck in. i tried to be gentle, but eventually the whole outer housing just sort of popped apart. and, more crucially, i broke one of the thin copper wires running to the electrical connector. i can still the the broken lead coming out of the coil, but its not connected to the switch.

it seemed like such a simple process. alas, i am a novice. i sort of pressed it all back together, put it back where it came from, topped off the coolant, and gave her a test drive. heat came on, no more coolant spilled out. but still, i have to go get the thing fixed now. yuck.

where did i go wrong? that thing was really wedged in there.

I just replaced my MONO valve insert yesterday and yes it seemed hard to pull up. I got the feeling it was magnetized? Someone more familiar with this valve could hopefully verify this. I know the coil produces a magnetized field to raise and lower the diaphram but I would think this would not be the case with the key off. I've seen alot of these units very rusty upon disassembly in wrecking yards. That would cause stubborn removal as well. Its best to remove this insert with a cold engine and the radiator cap off, no pressure. Less coolant loss.

yeah. my engine was totally cold, and i took the cap off. but still, the cooland poured out in about two seconds. on the other hand, it drained out into an area that was showing a leak sometime ago, so this at least suggests where the leak was coming from.

i put it all back together, and will fix it up tomorrow. im just wondering if i can drive it as is for now.

Assuming you are not loosing coolant , drive it!

yeah. the valve is in the open position, so i should just have heat, no?

I think so.

I recently changed my monovalve insert and am proud to announce that I no longer want to crash my car into a wall!! (long story). I removed the radiator overflow cap and reinstalled it prior to touching the monovalve. Try this next time as it may actually purge the remaining pressure from your cooling system and prevent anti-freeze from spilling on your driveway.

What's a "monovalve"...??
 

What in the world are you guys callin a "monovalve" that has to do with the cooling system... a thermostat???
Anxiously waiting to see if my brain has ceased to work,

It's a single plunger, heater core coolant whatsit, flow control valve doohickey, that works on a duty cycle doodah on the firewall by the battery thingamyjig.:D


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I'm guessing you didn't take off the coolant tank cap first....

The Monovalve is not part of a 1980 or earlier cabin heating system. On those 123's & 126's the 'Dreaded Servo' takes care of this function when it is working.

At any rate the monovalve operates in an on-off cycle related to the heat required and regulates the hot water flow to the heater coil in the cabin. It is not a variable opening valve, just has two positions.

Hey, I have a spare monovalve if anyone wants it.
 

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Hello All. :)

I picked up a spare monovalve at the pick n pull the last time I went.

If anyone needs one, I am willing to sell it. ;)

Just PM me here.

Thanks
RichC
:Peace!:

Thanks for the education...
 

Thanks for the information... so it's part of the dreaded " Environmental " system on these vintage MBz(s). Lucklily our 1980 240D is strictly a manual system [thank you Lord]... and when we tackle restoration of the 1980 300D's Heat/A-C system I'm hoping to find salvage parts from a 240D that will enable me to convert it to a manual system.

Do any of you guys have any thoughts on the pacticality of such a conversion? I don't think I would have to change any of the console "box"... just the control parts... and of course some to much of what's behind there. Does anyone know of some good system diagrams of these 1980 manual and automatic systems?
Regards,

actually, i did take the radiator cap off first, which is the strange thing. however, i had been having temp problems that i thought might have been related to a bubble in teh system somewhere. perhaps this had something to do with the fact. also, my coolant system had been staying under pressure endlessly, even when sitting for a while. i really didnt expect to have such a leaky situation at all, and wasnt prepared for it.

Current opinion seems to lean towards repairing with an aluminum bodied servo or the new digital replacement system. Easier than a complete swap of a manual system.