Aux fan overheating

[London 5]

My 2001 4.4 is overheating due to the aux fan starting but stopping very shortly after. Can someone suggest the part that might be at fault as the fan itself seems ok? Which switch/sensors need looking at?

I've had the thermostat, pipes, water pump, belts, rocker gaskets,
replaced recently.was also smoke tested.

Thanks

[TiAgX5]

Originally Posted by London 5

My 2001 4.4 is overheating due to the aux fan starting but stopping very shortly after. Can someone suggest the part that might be at fault as the fan itself seems ok? Which switch/sensors need looking at?

I've had the thermostat, pipes, water pump, belts, rocker gaskets,
replaced recently.was also smoke tested.

Thanks

My aux fan only comes on when the AC is activated. I've noticed it will cycle on and off when the AC system pressure drops below 35 psi measured at the low pressure port.

[Jeffatpm]

Mine would spin like one rotation and then disengage, I had to replace the aux fan. I think it was shorted out and pulling too much current so the computer cut off the power.

[London 5]

Thanks for the ideas, I’ve had the viscous fan replaced this week and still getting overheating when driven hard'ish

My wife has been driving it on the school run and shopping with temp running normal.

The garage noticed the radiator is only getting very hot at the top +sides, but the centre is cool to the touch. The suggestion is either the water pump (which is brand new) or a blocked radiator..

If anyone knows, are blocked rads common and what blocking them, can they be unblocked or just replace it?

If it’s blocked and the pump worked would the pressure go up if tested with?

Thanks for your help,

Ben

[SlickGT1]

I doubt you can unblock a clocked rad. Depends what clogged it. If it's a piece of metal, you are screwed. Not sure what else can be causing this. What coolant are you using?

[London 5]

I'm using Green Nulon which is ok for BMW I hear.

I've topped up with this, not sure what was in it before. I've since heard you should not mix them, so I'm planing to flush the system see if that improves it.
I'm also thinking the blockage may actually prevent flushing so I'm going to measure how much comes out.

How long should a radiator replace take?

Thanks

[TerminatorX5]

the fan on those years is placed in front of the radiator and is subject to the road elements, such as bugs and leaves getting in it... same design as in E39 6- and 8-cylinder cars (not sure about the 4-cylinder E39s). supposedly, if it is not turning, then taking it out and cleaning the bearings might revive the fan. some models used to have a resistor pack to control the speed (like in the AC system) that could have been replaced and that would have revived otherwise working fan... the newer models (i think, including yours) are using Pulse Modulated Wave (PMW) to control the speed, so there is no resistor pack to blame...

The electric fan by design is supposed to come during the AC load or if the regular can't otherwise keep the temp in check, say you are in Death Valley doing rodeo driving... This means, that if your AC is not on, chances that the fan comes on are very slim. Of course you could direct-wire it, so it is on at all the times, but I am not so sure what implication it may cause...

As far as your problem goes, you did mention that there was soome cooling system work done on your car recently - which begs the question...

did the guys put everything together right? there could be an issue with reinstalling the whole thing incorrectly...

Or, something as simple as an air bubble trapped in the system - then it needs proper bleeding...

[SlickGT1]

Term got me thinking with the whole cooling system work. How old is that thermostat?

Short trips, IE; school run and shopping is fine. Because water is in the warmup stage. Thermostat closed.

Driven hardish, thermostat needs to open but doesn't, can overheats.

Yes, I know, T-stats fail open, but I've personally had 2 BMWs where they failed closed.

Oh and put the blue coolant back in. Take out that strange mix.

[drgeeforce]

You have a fan directly attached to the water pump with a thermostatic viscous coupling. Turn on the A/C, the fan should engage. IF fan engages, then it is not the fan. If it does not engage, then the coupler is bad PN17417505109..
There's a temp sensor on the lower hose PN13621433077 and a double temperature switch PN13621703993 you may have overlooked.
Sometimes its an overlooked item like a fan belt not on the pulley.

[Isambard]

Put the beer down Slick and get your reading goggles on!

OP has already said the following : I've had the thermostat, pipes, water pump, belts, rocker gaskets,
replaced recently.was also smoke tested.

Clue's in the words..

Ben, I've just changed the rad on mine, fairly easy, just time consuming due to unbolting everything and disconnecting hoses etc.. Approx 2-3 hours total time.

Also, you might want to get one of these: eBay Australia: Buy new & used fashion, electronics & home d to get the viscous fan off to get the shroud out to get the rad out.. and breathe. Or make one yourself. Personally for the sake of a few quid I bought this and it did the trick nicely.

Edit: Oh, and you'll need to replace the heat exchanger X rings-2off. No.12 here: RealOEM.com * BMW E53 X5 4.4i Oil-cooler pipe/heat exchanger

Ian