I have a 2013 MINI JCW Hardtop which gave a yellow warning light that it was getting hot after about 10-15 minutes of idling. It was around 96 deg F outside temp that day. The coolant temp was 238 F degrees when I got the warning light and said drive moderately. I started to drive slowly and after 50 ft the temps climbed to 254 and red warning light to pull over. As I was going to pull over, the temp started to drop down to 200-220 degrees. I’ve driven it another time after that and temps fluctuate during driving from 175-200 and climbs higher when idling at a light. The coolant level was just a little above the MIN arrow so I topped it off to the Max level. The coolant level had stayed the same since, and I have checked for leaks but cannot find any in any of the hoses and the water pump side. Can’t really get a visual of the thermostat without taking parts off. I thought at first maybe my coolant just needed changing because it’s overdue for change, but then I noticed my heater was not warming up and just blowing cool air. It continues to overheat at idle and the radiator fan is running and goes into full blast after the temps reach. 228 degrees via Scanguage. Shop I called said the car will throw a code if the thermostat is stuck. Is this really true and is it possible that it’s stuck and just not throwing a code? TIA!

 

Try bleeding air from the cooling system.

When engine is cold, add coolant to reservoir until level is midway between max and min. Then run the engine and open the bleeder screw on the top of the thermostat housing until coolant flows out without any air bubbles. Then let the engine cool again and add coolant until level is midway between max and min in the reservoir.

 

Mine had a P0597 when mine failed. Wasn't overheating, just a persistent CEL

https://www.northamericanmotoring.co...cuit-open.html

 

^^ +1 Yep sometimes the internal electronic valve gets slow or error and since its emission related throw a CEL

 

Do all the coolant hoses get warm/hot with the engine running? Maybe it is just a faulty temp sensor.

There are two kinds of thermostat housings: one with an integral (non-replacable) and one with a replaceable temp sensor. The latter can be identified by the wired temp sensor (secured with a metal spring) from above.

Regarding coolant level: you can top it off until max level with no issues. In the worst case, it will release some from the fill cap when hot. It will make bleeding a bit easier (which should always happen with a hot engine and heating set to max, cabin blower set to min). I've been running my Mini with above max for years with no issues (never had a leak, never released coolant due to overfilling).

Practical bleeding procedure

PS.: I once forgot to re-latch the friction wheel after working on the water pump. The engine overheat warning came on when it run but no code was thrown.