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 atmo

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.