I think one of the better high volume acquarium pumps with 5/8 inch 
lines and all aluminum parts driven by a defroster motor's lowest speed 
would run a lot of heat through this cooling circuit.  The electrical 
load would be like other easily handled equipment.
  At least this isn't a rehash of old think.  
  I think the water cooled diesel and gas motor VW vans have plenty of 
radiator capacity, but the water circuit fails to supply the heat to the 
radiator.  That's why the fan's two speeds are so rarely called to an ON 
condition even though the motor may be well over the prefered operation 
temperature.  Move those coolants, be they water or oil, and this 
marginal situation may be brought within engine life extending limits.
LOVE IT,  seems we may be making some real progress.

John