overheating. how to diagnose a dead fan clutch?

[gareth]

firstly, apologies to anyone who takes offence about the E34 related content but i promise it's only a quickie and relevant to E30's too......


my wifes E34 (manual 525i sport, M50) is overheating:

the coolant level is fine at the moment but it does lose some over time. this has never got too low as it has a warning on the dash.

there is no obvious noise or discharge from the water pump and the belt is all ok.

the only thing i can see is the fan clutch... but i'm not sure! when it's a bit too hot (3/4 of the way on the gauge) the fan still spins freely by hand. am i right in thinking this should be locked up by this point?[/list]

[Brianmoooore]

If it's OK when moving along, and only creeps up when moving slowly or stopped, then it's probably the clutch.
If it overheats all the time check the thermostat, and your water pump.
If the waterpump has a plastic rotor then change it ASAP.
Now get that engine out of there and into an E30. It's wasted lugging all that metal around.

[gareth]

If it's OK when moving along, and only creeps up when moving slowly or stopped, then it's probably the clutch.
If it overheats all the time check the thermostat, and your water pump.
If the waterpump has a plastic rotor then change it ASAP.
Now get that engine out of there and into an E30. It's wasted lugging all that metal around.

it overheats even at a steady 50mph... i reckon it's both the fan clutch and maybe the thermostat.

that said, out of the five bmw's i've owned, i've had te water pump fail on 4 of them!

[Brianmoooore]

The fan clutch doesn't do anything at 50 MPH.
Early M50s had a notorious plastic water pump rotor which should be changed on sight. They break up and lodge shards of plastic throughout the cooling system. Unfortunately, they can't be identified without removing them.

[gareth]

i may just get a new water pump as a matter of course. the car is fairly early (J reg)...

it'll only cost Ԛ£20 - Ԛ£30.

which of B17018 or B1701/A on www.gsfcarparts.com right?

[Brianmoooore]

B17018A

[randomdave325]

to test your fan just leave it ticking over n when it's hot you should hear a difference when it kicks in n it get hot n draughty under the bonnet. when it's spinning try and stop it with a piece of rubber hose or rolled up mag (not your hand if u like it!!!). don't just jam it in there. rest it gently against the blades. if it stops then it's whiskered. if not you won't stop it easily (if at all). for the thermostat check if the bottom hose is getting hot. if not the thermostat is usually stuck. take it out n try again. if none of the above. then probably the dodgy plastic waterpump impellor. just chuck it n fit new. good luck

[gareth]

ok. i've had a play today so this is not 2nd hand wife symptoms!

the car overheats at any speed. the water level was a little low but not below the bottom of the expansion tank. the fan clutch is shot as it never tightens up, however, i don't think this is the real cause of the problems...

the bottom hose is cold!!! i've not investigated further due to lack of light. i've run the car around on several short trips and it's spent about 2 hours at around operating temp (sometimes a bit warm too) but the bottom hose is totally cold, not even a bit of warmth.

do these plastic water pump impellers totally disintegrate to the point that it wouldn't even heat the bottom hose? or does this level of cold indicate the thermostat sticking?

[Brianmoooore]

The plastic rotor can disintigrate to the point wher there is no circulation at all, and this results in local violent overheating in the engine, which is a good way to blow the gasket or warp/crack the head.
Thermostat stuck shut also gives a cold bottom hose of course, so I would check out both ASAP.

[gareth]

luckily i have a GSF dealer 5 mins from me and i know them well so hopefully i can order a fan clutch, thermostat and water pump and use what i need and return the rest... probably need all of them though! Ԛ£75 + vat for the lot though so it can't be all that bad!