I rebuilt my mono valve that had damaged rubber parts with a MTC kit. After that the coolant flowing through the valve would pull the valve shut, causing a "no heat at speed" condition. I have the valve out now and the flow blocked for summer. Are there any options for fixing this that would be less than $100?

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1984 300CD (sold)
1973 220DPK 4 spd (died)
1978 350SL 4 spd gray market
2003 SLK32 AMG
1988 300CE (sold)
1997 E420 (Totaled)
1998 E320 Wagon

The Bosch rebuild kits, which were never cheap but were reliable and lasted for years, are not currently available. The MTC kits used to be okay for 1-2 years but seem to now be complete junk.

There are threads on here where people have replaced the monovalve assembly either with one from a w124 - which has to be plumbed in where the aux coolant pump sits, as it's a different shape - and another where a member found a valve with equivalent function on eBay (I believe it fits in the stock location with a little adaptation).

Sorry I thought I had bookmarked both but apparently not....

IIRC both solutions came in under $100 for the parts (the used w124 valves seem to vary widely in price on eBay).

One forum member also advocates taking the entire monovalve unit off, disassembling it and cleaning it with CLR or an equivalent before writing it off. Some get very gummed up inside, more so if someone has run the car on "Prestone" in the past.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

I used the MTC kit and it did not work so I used the diaphragm from the MTC on the old solenoid. It has been working well for 4 months, I cant say about longevity, but you could do this many times before you've spent as much as the MB kit.

It's ashame you can't get a good kit anywhere. In the early nineties they were about $32 at the dealer. Lots of parts for older cars of all makes are no longer available with good quality. makes you wonder what it would take to go in business and make one. At a $100 a pop, you would think the business case could be made.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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