My 2008 mini s hatchback with Nav. It will randomly show engine over temp warning. It will be on for 30 seconds then go off. This can happen when i drive the car for ten minues into the drive or after driving for an hour. I purchased an app and bluetooth OBDII unit and this shows the temp will jump to 239 degrees then back to 170 all within a few seconds time. In a 20 minute drive around town in 68 degree F weather it showed the overtemp warning three times. I replaced the temp sending unit. Used contact cleaner on the wiring connector while I was replacing the sending unit and it still does it. The car does not seem to be losing coolant fluid and is running fine. I just bought it so this is a used car problem i seem to have inherited. The car had the timing chain replaced last summer and the water pump last summer also.

 

When we see these temps jump around like that it is usually the thermostat failing as it is freaking out. I'd replace it as they are common to fail before you actually overheat and potentially have other damage
https://www.waymotorworks.com/afterm...5-r56-r57.html

 

thank you for the advice.

I undcerstand what you are talking about the thermostat. How does it change the temperature that fast. it is really a matter of seconds that I see a change on my app.