M54 cooling issues. Help. My melon is in overload.

Pondy

Pondy

Muppet
 At the summit of the picturesque fens
My M54 3 litre has a cooling issue (I think). I know the M54 is a beloved engine on here, so am hoping for some proper knowledge.
The scenario......
The viscous fan just wasn't speeding up when coolant temperatures were getting high. I have an auxillary electric fan which was cutting in to cool the engine back to normal temps. So I concluded the viscous clutch was knacked. I installed a new viscous fan at the weekend (equivalent BMW part number).

I ran the car at idle in the garage and found the new viscous fan is 'cutting in' too soon. At around 60c the fan speeds up and temps creep up to around 75c at idle. Doesn't get warmer than that, no matter how long I leave it.
So today I took the car out and did a 20 mile run; a mixture of town and open roads and a couple of sitting in roadworks traffic. The coolant temp and the oil (obviously) never went above 75c. The ambient was warm, around 19c.

Have I got a duff new viscous clutch, or is my thermostat 'leaking' by, or something else?

I have gone from a lack of cooling of the viscous to overcooling in one fell swoop! It's doing my nut in.
 
The words "equivalent BMW part number" bring chills to my heart. What you get is always a gamble. I found an article where they test the fan on a Z3 with an infrared thermometer. Should open at 88 degrees
 

Attachments

  • Screenshot 2025-10-07 at 10-27-44 BMW E46 Fan Clutch Testing BMW 325i (2001-2005) BMW 325Xi (2...png
    Screenshot 2025-10-07 at 10-27-44 BMW E46 Fan Clutch Testing BMW 325i (2001-2005) BMW 325Xi (2...png
    298.3 KB · Views: 3
Is the combined effort of the electric fan and the viscous over cooling the engine?
 
bigwinn said:
Is the combined effort of the electric fan and the viscous over cooling the engine?
Click to expand...
No. The electric fan only ever comes in as a last resort (at around 100c). The electric fan is predominantly for the A/C, but it doubles as an auxillary cooling fan.
The new viscous clutch is engaging too early, but if the thermostat isn't opening it shouldn't make any difference should it? IE, the fan can run at a million miles an hour but if there is no water in the radiator, it ain't gonna do anything.

I have just swapped the clutch again; I've put the old one back in. When I removed it there was a lot of 'crud' on the metallic strip, so that could have been the problem all along. I shall try it again later.

I just don't quite understand what the problem is......viscous fan, thermostat, or both (or possibly neither!!)
 
I've got an E53 X5 3.0d and took the viscous clutch off that for reasons I forget years ago and just left it with the electric one. Even on the hottest day of the summer dragging a harrow uphill at 5mph it doesn't overheat. On newer cars the viscous fans have gone completely.

Have you changed the thermostat? Apart from the usual getting lazy aspects, something I remember from a friend's E39 was that the M54 stat has some sort of electric preheater in it to prime the stat to open promptly.

Also, is the temp gauge run off the ECM or is it just off a new sender in the block? The ECM version quantises the temperature into 5 blocks so 12 o'clock "normal" covers quite a range of temperatures that you'll suddenly start seeing on a trad gauge.
 
smorris_12 said:
Also, is the temp gauge run off the ECM or is it just off a new sender in the block? The ECM version quantises the temperature into 5 blocks so 12 o'clock "normal" covers quite a range of temperatures that you'll suddenly start seeing on a trad gauge.
Click to expand...
My temp gauge is from a new sensor in the block, but I am taking readings from the data via a scanner (just don't know where it is getting the info from). The car has two coolant sensors installed; one in the middle of the rad and one in the head under the intake manifold.

And yes, apparently the stat does have an electrical connection which is supposed to open the stat under high load (so I have been told).
 
Changed the viscous clutch back to the old one and it is doing exactly the same as it was before; ie getting to around 95c and the electric fan is kicking in and drops it back to 87c.

As said, the electric fan is maintaining the temps so I'm going to leave it as it is. Better to run a tiny bit warm than 15 degrees too cold I guess.
 
I thought normal operating temperature for an M54 was about 95C? ISTR that's about the opening temperature of the thermostat. If so, the fan ought not to kick in until well over 100C.
 
smorris_12 said:
I thought normal operating temperature for an M54 was about 95C? ISTR that's about the opening temperature of the thermostat. If so, the fan ought not to kick in until well over 100C.
Click to expand...
I don't know. I can't find much useful info. The internet is only interested in overheating issues.
If what you say is true, then the electric fan is kicking in before the viscous clutch. Maybe it is supposed to do this? Maybe the viscous fan is just there for decoration and the electric fan is supposed to do all the work? I just don't know!

I hate things I don't understand....and I don't understand what the problem is (if any).
 
In a dual fan arrangement, I'd expect the electric fan to only kick in at very high temps (excluding air con cycling) otherwise the viscous one is pointless.

Had a Google and I'm right. Normal operating temp is 94-98. No point running the fan until it's higher than that or you'll end up with over-cooling (which 87C is, IMO.)

Is the radiator fan being controlled by the ECM? Also, is it running full tilt when it runs? On cars just a few years newer I know the electric fan is PWM controlled so is variable speed - don't know the M54 well enough, but I'd have thought it'd be the same (edit: it is PWM controlled. Can be controlled though inpa to test.)
 
smorris_12 said:
Had a Google and I'm right. Normal operating temp is 94-98. No point running the fan until it's higher than that or you'll end up with over-cooling (which 87C is, IMO.)
Click to expand...
According to the info on my scanner, the electric fan cuts in at around 95c. It cools to 87c then shuts off. BUT.....I don't know how accurate the scanner info is. I don't know how accurate my gauge is, either (probably not very as it's an aftermarket and screwed into the block where the drain plug was). My gauge shows around 8c higher than the scanner data, so it shows around 105c when the fan kicks in and falls back to 95c ish.

And yes, I think the electric fan is two speed (not variable). It definitely only spins on low speed at idle, as you can't hear it over the engine noise. I only knew it had kicked in cos the temps started to drop.

BUT....while all this is going on the viscous fan just sits there 'ticking over' at around 200rpm. I have a piece of white tape on a blade which I can count. It's not very scientific but it helps.
 
BTW my A/C has been disconnected mechanically, so it isn't affecting any cooling.
 
Because I may have missed it......................... if the viscous fan is working correctly, why have you even got an electric fan fitted? I understand your car may not duct air as efficiently as the zed due to the kit, but on the M54 zeds I've had (quite a few now) it is extremely rare for the fan to run at all, unless the ac is switched on.
Maybe unplug the electric fan for a while and see if you actually need it?
 
enuff_zed said:
Maybe unplug the electric fan for a while and see if you actually need it?
Click to expand...
I thought about doing that, but I am scared. If the temps are not displaying accurately, how long do I leave it? I don't want to blow a head gasket just to check if my viscous fan works, or not.

What I don't understand (among many other things) is why my existing viscous clutch isn't engaging as it seems all OK. It has fluid in as I can feel the resistance. I know the metallic strip works as I checked it with a heat gun on the bench (don't know the temps though).
I also don't understand why the new clutch kicks in so early. It speeds up at around 60c, which just seems nuts.

Surely, as these things are purely mechanical and not connected to anything (except the water pump pulley) they are made so that the metallic strip bends at a certain temperature, then straightens at a lower certain temperature, which would be the same for any of them? I would have thought the only differences would be physical size, depending on the car/ radiator?

I could spend a lot of time and money changing thermostats, clutches, messing with the coolant system and still find it doesn't help as I don't know what the issue is, or even if there is one.
 
Pondrew said:
I thought about doing that, but I am scared. If the temps are not displaying accurately, how long do I leave it? I don't want to blow a head gasket just to check if my viscous fan works, or not.

What I don't understand (among many other things) is why my existing viscous clutch isn't engaging as it seems all OK. It has fluid in as I can feel the resistance. I know the metallic strip works as I checked it with a heat gun on the bench (don't know the temps though).
I also don't understand why the new clutch kicks in so early. It speeds up at around 60c, which just seems nuts.

Surely, as these things are purely mechanical and not connected to anything (except the water pump pulley) they are made so that the metallic strip bends at a certain temperature, then straightens at a lower certain temperature, which would be the same for any of them? I would have thought the only differences would be physical size, depending on the car/ radiator?

I could spend a lot of time and money changing thermostats, clutches, messing with the coolant system and still find it doesn't help as I don't know what the issue is, or even if there is one.
Click to expand...
I guess with your different temperature sensor set up, maybe that causes you an issue? Normally the fan speed is controlled from the DME, taking in various parameters, including temperature but also road speed etc (I believe). I wasn't actually aware it had any viscous coupling? I thought it was an electric motor that ran at different speeds according to the DME input?
Viscous fans are usually driven off the water pump pulley and do rely on the temperature to engage them.

My assumptions are based on you using a standard M54 set up? Have you had to bin the electric fan to fit your car? If so, why bother with the viscous fan at all? Just use the electric one, which will do the same job as the original Z4 item, but without the staged speeds.

EDIT: Hang on, you used a Z3 didn't you? Did that come with a viscous fan rather than an electric one?
 
Last edited:
Did you change your water pump?

It could be a symptom of a pump that’s not as efficient as it should be that the fans are doing something you wouldn’t expect
 
After consultation with my learned friend above, I think I would remove the viscous completely and rely on the electric one. I did it years back on my 2.8i Capri and it worked perfectly.
Also, if the viscous fan isn't working properly then to a slight extent it is disrupting the cooling airflow getting to the block.
 
Pondrew said:
I have been looking at those. They are just SOO cheap, I worry how accurate they can be?
Click to expand...
Accurate enough for my purposes - admittedly I haven't gone anywhere near the upper end of the range but I've compared it to my Thermapen which is supposed to be accurate +/- 0.3C and it always seems to be within 1C of it
 
You must log in or register to reply here.
Back
Top Bottom