Liquid cooled WWII aero engines generally used pressurized cooling systems, as this allowed running the coolant (usually a 70/30 glycol/water mix) past the atmospheric pressure boiling point. This, in turn, allowed smaller radiators, reducing drag.
The downside was that even a small rifle caliber hit to the cooling system caused the coolant to flash to steam and rapidly escape through the hole, giving the pilot only minutes until the engine seized.
The downside was that even a small rifle caliber hit to the cooling system caused the coolant to flash to steam and rapidly escape through the hole, giving the pilot only minutes until the engine seized.