Coolant system fucked?

Just release the pressure and wait and see if it happens again. If you want, start the car with the overflow tank cap open to see if any bubbles are coming up, which would possibly indicate a fucked head gasket (worst case scenario though). You should be fine, cooling systems are typically pressurized and designed to relieve pressure if it builds up too high.

>>16254090
Okay, but it felt like the coolant was ALL running out as soon as I open the cap. Don't really want to have to call the service to pick it up.

>>16254079
Worst case scenario? A blown head gasket can leak combustion gasses into the cooling system.
Give the coolant that came out a good sniff. If it smells gassy, then head gasket.

If not, then it might just be a temperature differential since the car cooled off last. Or, hell, maybe the expansion tank was just overfilled last time.

>>16254119
Sounds like overfilled then. I can't say for certain, of course. But if you can, put a big pan under where the tank is and just let it out, siphoning out the rest until the level is down to the full line. Shouldn't have to say, but don't fill it up to the top, there needs to be an air gap to allow for expansion. After you do this, if it happens again take it to the shop.

>>16254304
>>16254127
Alright. Tomorrow I'll check it while it's warm and idling. I'm taking it to the shop anyway, it's free to get it diagnosed.