Radiator fan on most of the time

[Robin]

I'm surprised how often my radiator fan's comes on even when not queued in traffic.
I even put the heater fan on directed up the windscreen to lose engine heat without heating me, but no difference.
Does anyone else find in warm weather their radiator fan is on for most of the time ?

[hornel Z3M]

I took my M out this morning for a 35 mile trip, stopped in lights went up to 90 mph, the needle on the temp gauge never budged (which i commented on the to other half)and the fan never came on once, so you may have some blocked fins in the rad or the thermostat is not opening wide enough, there must be a problem somewhere but at least your fan is working

[Badman gee]

I took my M out this morning for a 35 mile trip, stopped in lights went up to 90 mph, the needle on the temp gauge never budged (which i commented on the to other half)and the fan never came on once, so you may have some blocked fins in the rad or the thermostat is not opening wide enough, there must be a problem somewhere but at least your fan is working

Don't tell me you drove it Paul !

[hornel Z3M]

35 flipping miles. i hate knocking the mileage up.

[Badman gee]

35 flipping miles. i hate knocking the mileage up.

Far too much sir

[Robin]

I took my M out this morning for a 35 mile trip, stopped in lights went up to 90 mph, the needle on the temp gauge never budged (which i commented on the to other half)and the fan never came on once, so you may have some blocked fins in the rad or the thermostat is not opening wide enough, there must be a problem somewhere but at least your fan is working

Thanks. I better check out the whole cooling system. Especially as the fans' a drain on power plus waterpump bearings have a finite life & if they sieze they can take out the whole rad !
So the less the fan kicks in the better.

[Southernboy]

Here are the areas you must check:-
1. Viscous clutch on mechanical fan...if it's stuffed, it will spin easily and freely by hand. If stuffed...replace clutch.
2. Waterpump impellers broken. This prevents coolant being circulated....Replace waterpump.
3. Thermostat stuck in the closed position...very rare...mostly stuck in open position...but it can happen...replace thermostat.
4. All the above are in good condition...then check the correct functioning of the thermostatic switch fitted to the top left side of the radiator (left standing in front of the motor). It has a range of operation and generally will kick in when the coolant temp rises above 98.C or there-abouts...It is unlikely though, since the temp guage on the instruments is driven by a different temp sensor, and the temp / Fan switch operates independently...you are showing a high temp on the guage and an electric fan operating...this means your problem must be under items 1,2 or 3....

[Del]

The electric fan in my daily driver (not the Z3) is currently coming on very quickly (even before engine warmed) and I assumed it was something to do with the unusual heat in the UK (31 C in my front garden as we speak) and the car's aircon. system. If I turn the aircon off the fan stops.

[Robin]

Here are the areas you must check:-
1. Viscous clutch on mechanical fan...if it's stuffed, it will spin easily and freely by hand. If stuffed...replace clutch.
2. Waterpump impellers broken. This prevents coolant being circulated....Replace waterpump.
3. Thermostat stuck in the closed position...very rare...mostly stuck in open position...but it can happen...replace thermostat.
4. All the above are in good condition...then check the correct functioning of the thermostatic switch fitted to the top left side of the radiator (left standing in front of the motor). It has a range of operation and generally will kick in when the coolant temp rises above 98.C or there-abouts...It is unlikely though, since the temp guage on the instruments is driven by a different temp sensor, and the temp / Fan switch operates independently...you are showing a high temp on the guage and an electric fan operating...this means your problem must be under items 1,2 or 3....

Thanks SB.
My radiator blades are clear. Water level OK.

Del, Is the fan in the front for aircon ?
I never use aircon as doesn't work anyway.

The rear viscous fan feels slightly viscous when spun by hand even when engine cold. So I started up 1st thing today & noticed it spinning right away!
Can the coupling get too viscous too soon in this 30 degree weather before the engine's even heated or perhaps these fans never completely decouple in any weather?
I guess there's never going to be zero friction so the fan's always going to spin slightly but even with cold engine it seems to spin quite enthusiastically & as I say I can feel some drag when I spin it by hand.
I mean is this normal in hot weather or is my viscous coupling shot ?

[Southernboy]

If the viscous is shot...the fancan be stopped easily while the motor is running...to test this, start the motor, and use a rolled up newspaper and put it in the way of the fan...if it stops...the viscous clutch is US'd...get another one...
NB. there are aftermarket viscous clutches which you don't want to get...they never disengage...the result is it spins as fast as the motor, and it sounds like a jumbo jet revving up...they generally come from the far east...best is to spend the money and replace with an OEM unit. Hot weather has little to no effect on the function...it's more governed by the heat of the engine. The Aircon fan is in the front of the radiator and should only kick in when the aircon is swtched on. I have removed my mechanical / viscous fan completely, and replaced the thermo-switch for the aircon fan withan 83 degree thermo switch..it kicks on the aircon fan when the coolant temp exceeds 83 degrees...So, in effect it has replaced my mechanical fan, and I have done away with the drag on the motor which the viscous clutch imparts. As you see, I live in a "hot" climate, and the only time I have noticed my temp guage rise slightly above the mid point on the guage is when I'm stuck in traffic for an extended time...I simply turn the heater on full as well as the blower fan, point the hot air to the windscreen position and open the windows...the guage quickly settles back to the mid point..once the car is moving again, I can revert to "normal" function and turn the heater off...Ideally I'd like to fit a larger electric fan which will move more air through the radiator...but that's for another day...

[Robert T]

Um, I thought the newspaper stopping the fan was a good thing. When not locked the viscous coupling drags the fan round, providing some cooling. When it gets hot, the coupling locks and the fan speed will vary directly with the engine speed, such that if you blip the throttle it sounds like a propellor. When locked, the newspaper would not stop the fan.

Cheers R.

Sent from my Galaxy SII using Tapatalk 2

[Del]

I've seen mention of that test for the primary fan and tried it on mine. My understanding is that when the engine is cold the fan is "free wheeling", is moving more slowly and so can be stopped quite easily. When "locked" by a hot engine, it is revolving faster with the speed of the engine and cannot be stopped - if so, the clutch mechanism is no good. A rolled paper is safer than fingers but needs to be a "weak roll" with just a few pages so that it can be brushed aside by a properly working hot fan - without causing damage to the blades.

My 1.9 hasn't got air con and doesn't have a secondary electric fan. I guess this secondary fan is thermostatically controlled and is intended to cool the condenser for the air conditioning gas/fluid?

[Southernboy]

The viscous clutch only becomes operative when hot...therefor th test with the rolled up newspaper should be conducted when the fan is hot and supposed to be fully operational...if the newspaper can stop it when hot, the viscous clutch is useless...replace!

[Robert T]

I thought we were looking for a viscous coupling that is locked when it is cold, hence the reverse test I was doing.

It it is locked when cold, replace. If it fails to lock when hot, replace.

Cheers R.

[Robin]

If the viscous is shot...the fancan be stopped easily while the motor is running...to test this, start the motor, and use a rolled up newspaper and put it in the way of the fan...if it stops...the viscous clutch is US'd...get another one...
NB. there are aftermarket viscous clutches which you don't want to get...they never disengage...the result is it spins as fast as the motor, and it sounds like a jumbo jet revving up...they generally come from the far east...best is to spend the money and replace with an OEM unit. Hot weather has little to no effect on the function...it's more governed by the heat of the engine. The Aircon fan is in the front of the radiator and should only kick in when the aircon is swtched on. I have removed my mechanical / viscous fan completely, and replaced the thermo-switch for the aircon fan withan 83 degree thermo switch..it kicks on the aircon fan when the coolant temp exceeds 83 degrees...So, in effect it has replaced my mechanical fan, and I have done away with the drag on the motor which the viscous clutch imparts. As you see, I live in a "hot" climate, and the only time I have noticed my temp guage rise slightly above the mid point on the guage is when I'm stuck in traffic for an extended time...I simply turn the heater on full as well as the blower fan, point the hot air to the windscreen position and open the windows...the guage quickly settles back to the mid point..once the car is moving again, I can revert to "normal" function and turn the heater off...Ideally I'd like to fit a larger electric fan which will move more air through the radiator...but that's for another day...

I like the sound of this. Thanks for the tip. I think the the viscous driven fan is more of a drag on the engine than is needed for much of the time. Electronic control of the aircon fan will be much more efficient. Whereabouts is the aircon thermoswitch & where did you install one to measure the water temp instead ?

[Southernboy]

The thermo switch for the fan is on the left top side of the radiator - viewed as you stand facing the engine - It simply screws out of the side after you detach the wiring connector. The engine temp to the instrument cluster guage is located on the engine block near the water pump area if I recall...
You can get an 83 degree thermo switch from BMW as an OEM part, I seem to recall it comes fitted to some of the newer cars which don't have a viscous fan any longer, but your local BMW dealer will help there. Also, you will need the plastic connector to replace the one on the car, as they are different...also available from BMW...then it's a matter of draining coolant from the drain plug under the radiator, unscrew the old switch / replace with new switch / and fit the new connector to the existing wiring / re-fill the rad (after replacing the drain plug)...Whilst you have the rad drained, unclip the 2 radiator clips at the top left & right, and using a 32mm socket with a long lever, undo the fan nut - it's a reverse thread, and what you do once the socket is on the nut, is give the lever a sharp smack from the left to right and the fan nut will come loose....spin the fan off, and by manoevering the rad /fan cowling out the way, you can lift the fan up and out. If you ever want to replace the mech fan...the reverse procedure is required...although you don't have to drain any coolant....just do all these tasks when the engine is cool!!!

[Robin]

Many thanks SB. Will be good to ditch the somewhat primitive & power wasting viscous fan.