SHELLNEKOV, Please put year and type of car in your profile then you wont get Ford, Chevy? answers. The mono valve was used from 1981 thru 85 in the 123 chassis, thats why the year of your car is important. The aux water pump works at idle and low RPM to force the coolant up hill to the heater core. Electrically failed, cool air at idle. Not needed once the water pump is spinning fast enough. Simply remove the 4 screws holding the cover on the mono valve (ENGINE OFF AND COOL) reach in and lift up the internal shaft and rubber diaphram. Note how the stacking of the washers go so it goes back together properly. Pull out around the diaphrams circumference and look for a tear in the rubber. Torn, needs a mono valve repair kit. Assembly filled with rust? needs a new mono valve.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.