That's real funny, because the three vehicles I've found (in my lifetime) with rusted/ busted pump impellers were not producing any heat in the heater AND the hoses were not getting hot. "Warm" maybe.
You must have the magic truck, because what you describe goes against all theory of heat exchangers. For the record, I worked in the HVAC industry for about 12 years, and liquid -- to liquid and liquid - to air heat exchangers were 'part of the deal.'
Is it possible that the hoses were heating up from the exhaust manifold radiated heat?
