Since I have heat but very weak heat at idle, I know I have a bad auxiliary water pump (91 300D). However, the heat when I'm moving, while pretty good, does not seem as hot as it should be.

My question: does the auxiliary water pump contribute to any significant degree to the system's ability to heat the cabin when the car is NOT idling?

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 160k miles
06 E320 CDI "Rutherford", Black on Tan, 180k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 79k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife