Radiator Cap - Update My Prevent Coolant Loss

85mercedes03
TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS

DATE: December 1985 REF. NO. 20/34

SUBJECT: COOLANT LOSS THROUGH A FAULTY RADIATOR OR EXPANSION TANK CAP ALL PASSENGER CARS (EXCEPT MODEL 124.030 AND MODEL 126 WITH ENGINE 116/117)

Figure 1 - Radiator Cap:

The reason for coolant loss (at approximately 110~C) may be a faulty pressure/vacuum valve in the cap.

NOTE: This seems to be more apparent in caps made by Reutter, which have a plastic valve plate (arrow, Figure 1).
In these instances, the first step is to replace the radiator cap.. If this does not correct the problem, replace the expansion tank (check for a damaged or weakened filter neck). If the above steps are ineffective in correcting the problem, perform the related tests (i.e. Pressure/leakage test).
Parts Information

Part Name Part Number

Cap 123 501 02 15