Cooling Fan only working with AC on

[2wheelsoff]

SOLVED - Expansion tank leak didn't allow pressurization. Leak was at the evacuation hole where the cap purges fluid ...very elusive...video at the end of the thread.


Hi all,

I have searched and not coming across the same issue. WP and Thermostat are less than 7k miles old, 3.5i N55 motor 77k total miles 2011 x5.

When towing, with AC on the engine heat soaked and started boiling over, when I parked it for 5-7 minutes.

I had a low coolant warning (know level senosor functioning) the week before and topped off (1/4 gallon of distilled)...thinking it just boiled over at some time due to some hot weather we've been having in Denver.

I lost just over 1 gallon of fluid in the parking lot and was still 45 mins from home. I let it cool for 30 mins, filled with distilled (was towing home from autocross so had water with me for the racecar luckily), then ran the bleed procedure on the electric WP. I blasted the heat and drove home without issue, until I parked it at home...same issue, heat soak led to boil over....once it started bubbling, I ran the coolant bleed procedure to keep the water circulating through the radiator.... I only lost about 1/3 of a gallon.

I figured out the hidden menu unlock and have been watching the temp...with AC on the fan works and I maintain less than 96 degrees C ...usually highway driving = 87C + or - a few. I let it heat up to 99C with the AC off in the driveway and fan never kicked on, run AC and cools it down to under 90C. Shut off and heat soak brings it to 97-100C no Electric fan after run either.

I also never received the orange limp mode warnining nor the catasrophic RED warning to shut down.

From this research

TIS - https://www.newtis.info/tisv2/a/en/e...ooling/XnZEwDx

https://www.newtis.info/tisv2/a/en/e...c-fan/CkYajpf4


Question is shouldn't the relay K9137 be energized via AC being on, and then other than the DME not signaling correctly...any other options that would cause the failure? Coolant Sensor is showing temp on dash and seems right.

I am seeing that the only part I can see that would have failed is the relay or fuse 171 (100A) going to the relay. I am thinking diagnostic is to just jump the 30 and 87 pins on the relay when the temp is above 97 as long as there fuse is not blown and 12v at pin 30 on the relay (K9137 below), with AC OFF.

https://www.newtis.info/tisv2/a/en/e...sav/1Vnc2EMKWo

any help is immensly appreciated. I am proficient in 80's - early 2000's BMW's but at a loss here.