I would check the amperage of the auxillary pump while driving. If it is contiuous and not over 1.3 amps you are fine. I have seen the aspirator pump fail on these causing the in car temp senor to be strange.

The service CD has this system in detail. we have them in partsshop.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM