Joe, I forgot to answer that one.
The coolant loop going through the coach on coaches of that vintage got generally acceptable flow rates to provide the necessary heat because of the engine pump.
I suspect because Prevost was from Canada that they were more sensitive to having a coach you could heat so to insure in extreme cold that sufficient amounts of engine coolant made it from the engine to the windshield in particular, and other area a supplemental pump was provided.
On my 87 that pump was mounted low, passenger side, near the engine, and I do not know if our respective converters moved the pump or if Prevost made a design change between your 86 and my 87. In my 87 Liberty installed heat exchangers with fans in numerous places such as under the sofa, under the bath vanity, under the dinette, etc. Those heat exchangers were part of the cooling system and I was of the opinion the small pump would provide additional flow to them as well.
FWIW Prevost sold parts for that pump and I replaced the brushes once. I do not think that pump has anything to do with controlling engine temps except to the extent the heat exchangers throughout the cooling system would reduce the coolant temps to a degree, but there was no way I would use them to cool the engine on a hot day.
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