Re: Rear hydronic heater & under bus piping
Failure to communicate. Hydronic heat is a system that heats water, and circulates it through a loop with radiators or air to water heat exchangers of some sort. Technically an automotive heating system is one, never heard the heater core described as a hydronic heater. A lot of school buses have a diesel fueled boiler that heats the coolant to aid in cold engine start and fast warmup for the kiddies. I use a Espar hydronic heater for my heating in the bus. Full boiler system with both in floor tubes and also an air to water heater core in each room for additional heat. The engine is only in the system with water to water heat exchanger for heat when the bus is running.
To answer your question yes, theoretically it would aid in cooling the engine. We used to run our heaters full blast in sports cars in parades to help keep them from over heating at those slow speeds. I don't think it would make a hill of beans difference in a cooling system the size of a bus. In standard bus cooling system, when you turn off the heat, you turn off the water to the rear heaters, so it isn't in the system when you might possibly need the extra cooling which is in hot weather.
Buses are basically trucks, made to carry and tow loads. Unless you are pulling something really heavy or big, if the cooling system is working properly you won't have any problem.