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.

[2wheelsoff]

Update - fuse 171 shows continuity (located on top of the battery)

[80stech]

It sounds like your coolant is not strong enough. Water boils at 100c

[ard]

OE, OEM or aftermarket WP and Thermostat?


I think the cut out relay provides power to the Fan. As long as the control signal on Pin 1 is powered it should conduct power to the fan.


That relay isnt controlling the fan. It controls the POWER to the fan


The fan itself is controlled on pin 4 of X1797 ..and that signal is a PWM signal.




and I dont think it is coolant 'strength'....


DO NOT jumper any of that.


You should monitor the wire to that relay on pin 1, and also the two heavy red wires on X17278, X17279 and see that they are indeed 12V and stay that way when driving and in the driveway.


Any reason to suspect some of the other temp sensors?? (which the DDE uses to decide when to run the fan...)

[2wheelsoff]

Thanks for the response ard,

I'll diagnose when the relay is getting power to control signal (terminal1) tomorrow... I don't think the problem is the relay as the fan is on (and adjusts speed according to temp when AC is on).

What other temp sonsors are there in the car? According to the diagram it only shows one temp sensor at the top/front of the head. I also checked realoem and not seeing other coolant sensors.

I agree it isn't coolant strength (lemons car we only run distilled, or tap water in a pinch) and holds temp. BMW runs at 2 bar = boiling 120C.

I am thinking maybe the cap is failing and not holding pressure...ordered one.

Water pump is Continental, and Tstat is Wahler. Fluid is BMW oem...though right now is 70-80% distilled.

Thanks again...stumped still.

Originally Posted by ard

OE, OEM or aftermarket WP and Thermostat?


I think the cut out relay provides power to the Fan. As long as the control signal on Pin 1 is powered it should conduct power to the fan.


That relay isnt controlling the fan. It controls the POWER to the fan


The fan itself is controlled on pin 4 of X1797 ..and that signal is a PWM signal.




and I dont think it is coolant 'strength'....


DO NOT jumper any of that.


You should monitor the wire to that relay on pin 1, and also the two heavy red wires on X17278, X17279 and see that they are indeed 12V and stay that way when driving and in the driveway.


Any reason to suspect some of the other temp sensors?? (which the DDE uses to decide when to run the fan...)

[80stech]

Why are you thinking that there is a problem with the fan? Having a boil over after hot soak at 100c isn't the fan's fault. If the coolant was even close to being strong enough it would not boil at 100c even if the pressure wasn't holding.

[2wheelsoff]

Originally Posted by 80stech

Why are you thinking that there is a problem with the fan? Having a boil over after hot soak at 100c isn't the fan's fault. If the coolant was even close to being strong enough it would not boil at 100c even if the pressure wasn't holding.

Not sure what the temp was when boiling over, has to be well over 100c first time when it dumped 1 gallon. it is bmw coolant 50% mix... Re read first post, diagnostic temps are after the boil overs happened... Pure distilled will boil at 120c under normal bmw coolant pressure. Thinking it's the cap

[ard]

Originally Posted by 2wheelsoff

Thanks for the response ard,

I'll diagnose when the relay is getting power to control signal (terminal1) tomorrow... I don't think the problem is the relay as the fan is on (and adjusts speed according to temp when AC is on).

What other temp sonsors are there in the car? According to the diagram it only shows one temp sensor at the top/front of the head. I also checked realoem and not seeing other coolant sensors.

I agree it isn't coolant strength (lemons car we only run distilled, or tap water in a pinch) and holds temp. BMW runs at 2 bar = boiling 120C.

I am thinking maybe the cap is failing and not holding pressure...ordered one.

Water pump is Continental, and Tstat is Wahler. Fluid is BMW oem...though right now is 70-80% distilled.

Thanks again...stumped still.

I was just looking at the diagram... B6236a and Y6279. The latter being unfamiliar.


Cap is cheap enough....b

[2wheelsoff]

Originally Posted by ard

I was just looking at the diagram... B6236a and Y6279. The latter being unfamiliar.


Cap is cheap enough....b

The Y6279 is the heater in the thermostat to force it open under certain conditions controlled by the DME.

I just found temp sensor B604 comes out of the radiator...it isn't showing on the engine cooling wiring diagram...thinking it is part of the heating system..or was overlooked in the TIS...though doubt it.

https://www.newtis.info/tisv2/a/en/e...utlet/DvBACO5I

Cap arrives tomorrow.

[ard]

B604 exists on E53 diesels.....input to DME, controls fan


Weird