Hi,
OK now -
BREATHE... You should be completely OK. 1/4 Cup is equal to 2 fl. oz. of Window Fluid which is pretty much 50/50 water/isopropanol, so you have 1 fl. oz. of purified water and 1 fl. oz. of rubbing alchohol. Before the advent of ethylene-glycol, early antifreeze was a water/isopropanol mix.
In a 4.5 gal. system, that equates to 0.17% dilution. Your Car won't even know it's there. The alcohol will eventually vent to atmosphere and in the meantime, will actually reduce the surface tension of the coolant allowing it to shed heat more easily and run cooler (won't be noticeable, but it will) - this is how Water Wetter works. Better now...??
RELAX... but don't let others mess with your car in the future 'cause you never know what they're gonna do. Good thing it wasn't a Qt. low on Oil...
Happy Motoring!... Jim'99
BTW, if yours is a '99 (ALWAYS state model year when asking advise - the coolant capacity varies) it's not a bad idea to plan on a flush and coolant replacement. Porsche says it's lifetime fluid, but it ain't, the corrosion inhibitor package breaks down in this lifespan and needs to be replaced to preserve the integrity of the cooling system components. 5yr./150k mi. (whichever comes first) is the longest any coolant should run. Also, be sure to replace with any
phosphate, silicate, and borate-free Coolant such as Prestone 5/150 Extended Life, Sierra and others.
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