I replaced the valve with an aftermarket valve. The faster I go, the less heat I get. Seems like the dynamic suction is pulling the valve closed. Is this the problem? If so how do I fix it?

A lot of the aftermarket valves don't work properly, even when new...

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

one solution is to pay $150 for MB monovalve. Another is to put a rubber o ring between of the valve and the water inlet. This keeps a stream of hot water flowing at speed. You will need to remove it to get max AC in the summer.

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1990 350 SDL
Currently: 180,000 miles
Factory rebuilt bottom end rods, bearings and head gasket @ 75,000 in 1997

I was not aware Bosch valves were still available

Try running with the monovalve electrically disconnected. Do you still lose heat at speed?

Sixto
83 300SD
98 E320 wagon