Viscous fan failed

Fri Jul 24, 2009 8:04 pm

The fan on my 318is isn't cutting in when it's hot, resulting in the expansion tank overflowing on Wednesday.
Is this likely to be due to a knackered clutch in the water pump? How easy is it to fix or replace?

Fri Jul 24, 2009 8:19 pm

The clutch is in the fan itself,have you done the newspaper test?

when the engine is hot (when fan normally kicks in) try and stop the fan with a rolled up newspaper,if the paper gets shreaded its working fine,if the newspaper stops the fan the clutch is foiked

Fri Jul 24, 2009 9:10 pm

Overheating can be other issues as well on these 20 year old motors,a radiator that passes the 'hosepipe' test could well be blocked with crud.
The water pump could also be past it's best and the water jacket could also be full of silt,causing the system to run hot due to poor circulation.
Thermostat may be failing to open/shut at the required point as well.
Is the heater getting hot?If not,you have a circulation issue.
Hope it's the viscous fan coupling,as that is an easy,cheap fix!

Sat Jul 25, 2009 12:04 am

leeparkes wrote:The clutch is in the fan itself,have you done the newspaper test?

when the engine is hot (when fan normally kicks in) try and stop the fan with a rolled up newspaper,if the paper gets shreaded its working fine,if the newspaper stops the fan the clutch is foiked

The fan doesn't kick in at all even when the temp gauge was up in the red. Electric fan would be easy to test but I don't know much about the viscous system.

Sat Jul 25, 2009 12:32 am

If the gauge has reached a position where the fan should obviously have cut in (don't need newspapers - it roars if you rev it when then coupling is locked), then it's a fair bet that the coupling has failed! Only other possibilities are gauge problems, where the coolant isn't as hot as you think, and a partially blocked radiator, where the central area that triggers the coupling is cool.

Sat Jul 25, 2009 1:37 pm

I'm guessing it's the coupling, is it an easy fix?
Won't be the gauge as the expansion tank overflowed due to the temp it reached.

Sat Jul 25, 2009 1:58 pm

easy to change the fan clutch, but you need a big open ended spanner (32mm IIRC) the thread is reverse thread so get the spanner on the nut (its on the front of the fan centre) and hit it the "wrong" way to loosen it. once the fan is off it will be obvious how to change. Easy on a four pot as plently of space to get the spanner on the nut.

however one question you dont answer (and i am surprised Brian didn't pick this up!!) does the car over heat when on the move (i.e. over 20 mph) or only when you come to a stop.

if the answer to this question is yes then the problem is not the fan or fan clutch...look for knackerd waterpump, blocked radiator, faulty thermostat (or even a removed thermostat...never do this) or finally the biggie...head gasket

mrlee

Sat Jul 25, 2009 2:53 pm

mrLEE30 wrote: one question you dont answer (and i am surprised Brian didn't pick this up!!) does the car over heat when on the move (i.e. over 20 mph) or only when you come to a stop.

That's 'cause I don't always read all of the thread!

Sat Jul 25, 2009 3:54 pm

so many problems so little time to answer them!!!

you should ask Steve to get you a zone secretary!! A saucy one too!!

Tue Jul 28, 2009 7:59 pm

Like the idea of a saucy secretary, can you get me one too!!

General driving it's fine, I've never had a problem and the gauge sits at about halfway once warm. It only got really hot when I was at a drift day last week and it even boiled over the header once. To stop it happening again I just drove round for a couple of minutes to get the airflow through the rad and it returned to normal pretty quick. I'd imagine I'd get the same problem if I got stuck in heavy traffic.

Wed Jul 29, 2009 10:02 am

^^^ classic case of a tired viscous clutch in my view. If you're doing stuff like drifting, you'll want to make sure the cooling system is tip top, escpecially things like the radiator and viscous fan. Would be worth giving it the once over and replacing some of the more tired elements in my opinion...