The high boiling point and concomitant lack of pressure in the system sounds quite tempting. A small leak would present a much lower hazard.

        The greatly reduced heat transfer abilities of NPG make me think twice. This pretty much guaranties that the engine will run hotter than it would on water and EG, everything else being equal.

        The higher viscosity means that the pump will suck up more HP, but the higher boiling point means that it won't easily cavitate.

        I would also think that any severe hot spots (like the area near the spark plugs) would go to 375 and boil anyway. Is the extra 150 degrees a problem? Who knows?

        Bill Dube'