I am having an overheating issue that I'm hoping someone here might shed some light on. I have a 2006 R50 with 89K miles. My commute takes me a mile or so to the freeway entrance, another eight miles on the freeway, and then another mile of stop and go to the parking garage at work. This time of year (+100 during the day) I always have the AC on high. A month ago I pulled into the parking garage and noticed that the coolant temp had jumped from the halfway hash mark to full/red. Since then I have driven the car with the centre display in diagnostic mode, showing the temp in degrees celsius, and I watch it constantly. A handful of times since then I have pulled into work and watched the temp suddenly start climbing from the normal operating high of around 95 degrees up to 107, 108 degrees. I then shut the engine off, but not before I pop the hood and quickly confirm that the radiator fan is not running. The radiator fan relays and resistor test ok. I am not losing any coolant, and my thermostat seems to be functioning. Any ideas? Thanks in advance.

 

Did you say the fan is NOT running?
when a mini is very hot hot, the fan may still run a bit after you turn off the key....
is the fan ever running??
Do a search....it is a 2 speed fan...low (quiet), and hi (loud).
Coolant level ok...full....if it has been run low...it may have an air bubble...
Has the coolant ever been changed...it is not longlife (it does not fail, but the anti corrosion addatives do get depleted....allowing dammage to occur in the system....

 

The fan runs when I first start the car with the ac on. I've tested the radiator fan resistor and relays using a test I found on a post here where you connect it directly to the battery and ground. The car runs normally until the stop and go traffic at the end of my commute, basically when I pull into the parking garage at work. The temp starts climbing as soon as the fan stops running, and continues climbing even if I turn off ac and turn on heat. Coolant system was drained, flushed, and refilled one year ago. There are no leaks and it has not run low since. Just started doing this as the weather became really hot here.

 

Oveheating in stop and go traffic/slow speed situations might point to a lack of flow....either coolant (worn water pump)or sticky thermostat, or possibly a plugged radiator...(ever use stop leak?)or lack of airflow....if the fan does work as intented....and the test you did only rules out the actual fan...not the wiring or even the programming...
Check the belt for signs of slippage....while at it, look at the waterpump weap holes...look at the simple/free stuff first. Good luck.
Reread reply....fan stops...look there...see below.

 

PS
The fan should not stop running till a pre-determined temp is reached...
I would focus on WHY THE FAN STOPS....when the car is close to overheating, the fan should be on high....and stay on till a minute or so AFTER THE CAR IS OFF.

 

Thanks Zippy. I will look at those items you suggested. I also ordered and received a Peake code reader today, thinking that might tell me if it is a problem with the ECU. I was under the impression that when the ac is on, the fan will always be running, regardless of temperature, and when the ac is off the fan will kick into low at 105C and high at 110. This problem seems to happen when the temp is around 98 or so, and then it begins to climb quickly once the fan shuts down.

 

The ecu should keep the fan running if the ac is off...
the numbers you listed seem right....first low....till a higher temp is reached (like a hot day, little airflow), then hi kicks on for a bit to drop the temp down....
The high I think will cycle a bit, but the low should be running inbetween....even with the ac on. I wonder if the test you did with the fan is accurate....but the code reader (if it is like many) let's you read more than codes, and let's you see engine parameters....fan on off temp readings, etc.