Driving my Mini on a warm day, the coolent rises above the 180deg where it stays during cooler weather. In 95deg heat the coolent will rise to around 210F; while this isn't a big deal, it bothers me that it is rising at all. To me, once the coolent temperature starts rising, it means the thermostat is now 100% open all the time, and the radiator is no longer able to do its thing - the system has reached it's full cooling capacity. While there are a number of things I'm going to try to improve cooling capacity, it brings up a question.

How do you guys define "overheating"? Is there a magic coolent temperature above which you'd worry. Or, is it all good as long as the coolent isn't boiling, regardless of temperature. In other words, how do we know how hot is too hot?

 

I define overheating as: if the coolant stays in the system without boiling out, and nothing break, it isn't overheating. However, be sure to give it plenty of cool down time if you push it much past the normal running temp before turning it off.

 

So then why not just replace the 16lb cap with a 24lb cap to raise the overheating limit?

 

I would probably start worrying when I saw anything much over 220-230. Since the water in the system is under pressure, it won't boil at the normal 212. Even during the hot days here, I usually don't see my water temp above 210-215.