N18 boiling coolant
 

Ok so I just opened the hood this evening after a short drive. I noticed the coolant was boiling in the expansion tank. It got me scared immediately. As I slowly Opened the cap lots of coolant spewed from underneath the cap. What do you think could be the cause of this? My ultragauge has my car always in the correct temperature operating window, 222.8 when warm and around 200-205 degrees in sport mode. Any suggestions as the cause of this boiling? When my last mechanic finally fixed my oil pan gasket, I saw that he slightly overfilled the coolant reservior when he topped it off. But I didn’t think much of it. But I’ve now heard that this could cause some boiling. So yeah I’m hoping it’s either this or a faulty old reservoir cap. Just really hope it has nothing to do with the head gasket lol. Any insight would be appreciated. Thanks fellas

It could be a stuck closed thermostat or as you mentioned a reservoir cap?

Thanks for the input. My temperatures have always been in the normal range. If it was stuck closed wouldn’t I overheat a bit?

Update: when I opened up the coolant tank cap that one night, loads of coolant spewed onto the ground. After that, I closed it back up and the coolant level was actually right near the level where it should be. After that i let it sit overnight, and the coolant level was right near the “min” level like it should be when cold. The car has been running fine ever since. No boiling or anything since then, and all running temps are still normal like they previously were. I think my coolant was just extremely overfilled by my last foolish mechanic to cause this issue. Anyways, Looks like I’m good to go for now. As always, an extra input is always appreciated. Thanks fellas-Blake

Maybe just a Thermostat glitch? Like.... it got stuck closed for some reason?
Either way, the thermostat and housing have always been an issue, so if it happens again, I'd just swap it out.

I do find it interesting that you are running 222 degrees, and around 200 in sport mode. Im usually around 210 in regular mode, and 175-180 in sport mode :/

Yeah it still hasn’t happened again knock on wood. After a lot of reading it seams a lot of people here have cars running around 222 and say it’s completely normal