Rad Fans

[strummer]

Been away to lakes for a few days,going over Wraynose Pass very slow and very hilly temp gauge started to creep to red,just got to top before it hit boiling point,coming down the other side picking up speed the needle returned to normal.
Just checked rad fans,with engine running with air con on fan behind the rad,closest to engine was running the one in front wasnt,is this normal?How are they supposed to operate and what is the method for testing them?
  thanks

[henrym3]

If your a/c is on the aux fan should be running, also if your engine gets so hot the viscous fan can't cope the aux fan should kick in to help out. You didn't mention it but I assume you have checked the coolant level. I believe it is not uncommon for the aux fan to fail. As a basic check just see if you can turn the fan easily by hand to confirm it hasn't seized.

[strummer]

coolant level is fine,the aux fan is the one in front of the rad bumper side of the rad?

[henrym3]

correct,I should add that your viscous fan attached to the coolant pump should be able to cope with engine temperature on it's own, it's not like it gets that hot in this country. I assume that when you were going over the pass you had the a/c on.

[strummer]

just checked aux fan it is spinning freely when turned by hand,where next?

[henrym3]

when was the system last gassed, do you get cold air at any stage.

[strummer]

not gassed for last 5 years air con works well

[X5Sport]

It probably needs checking as these systems lose gas.  Can it cope with 16C on a hot day?

It sounds like you have enough gas if the a/c is running but it will very likely need a top up.  Mine was at about 50% when pressure checked but still ran the a/c (just) at 5 years from new.

The viscous fan should turn with the engine running, but possibly more slowly and as the system warms up will then lock in and run at engine speed.  The electric fan should run with the a/c and will ramp up speed wise if the engine temp gets too high.  With a cold engine you can (very carefully) stop the viscous fan but not on a hot engine!

I have never seen my temp go over half way even when buzzing about in the Welsh Mountains, but I have heard the electric fan running like a jet engine in those same circumstances.

You might have a faulty coupling in that it isn't engaging at high temp so not enough ram air is going through the rad.  It could also be a sticky thermostat not fully opening.

[henrym3]

Well, if your a/c works well at idle and at speed, I freely admit to being stumped as to what your problem is. As for the overheating of the engine, if coolant level is good and coolant is in good condition then possible a loose coolant pump belt or sticking thermostat.

[strummer]

If the air con needs regassing would that stop the aux fan running?

[Steamyrotter]

Yes.

There are pressure switches for over and under pressure that protects the system

[strummer]

Checked pressure in air con which was 35psi which is apparently spot on,checked for voltage at plug connector for aux fan which was 12v so ok as well,with engine running occasionally the fan would move a bit and then stop so looking like fan is faulty?Has anyone changed one?

[X5Sport]

The fan uses a 12V pulsed signal so a reading of 12V may not be the whole story.  The system varies the pulse length to change the fan speed.

Not sure if you can get the fan from anywhere but BMW and they want silly money for them 

A couple of folks on here have played with replacement electronics but it wasn't simple.

[Smeeagain]

[quote="Steamyrotter"]
Yes.

There are pressure switches for over and under pressure that protects the system
[/quote]

apologies if Im slightly highjacking the thread - is there a way to test the pressure switches?

Smee

[X5Sport]

Only with pressure.  They are usually just an on/off switch moved by pressure.  If you have enough gas then I would expect it to be a short circuit between the pins, open circuit if insufficient pressure present.