M54 engine viscous fan. Not sure if I have an issue.

[Pond]

I have a feeling my viscous fan on my M54 (3 litre) is not operating as it should. I have searched about this but am still confused.

So...here is my scenario....

My viscous fan runs from cold but doesn't seem to speed up (much) when the engine gets hot. It does alter it's speed but not by much. I tested it by putting a bit of white tape on one of the blades and watching it with a torch shining on it.

The engine gets to operating temperature (90c ish) then slowly gets hotter. All the time the viscous is running, but it doesn't change it's speed much at all (but does a bit).
When the engine gets just over 100c, the auxillary/ A/C electric fan kicks in and cools the engine back to 90c ish but the viscous doesn't change, it just keeps 'ticking over'.

I am not sure this is the way it is supposed to work. I was under the impression that the viscous should maintain temperature and the electric fan is only there if more cooling is needed that the viscous can't do when flat out.

Can someone please confirm whether my viscous is playing up, or this is normal with this engine?

 

[AntStark]

In all the time I’ve owned my 3.0 the only time the electric fan has come on is when I activate the (non functioning) air conditioning. The viscous fan does all the work.

 

[Rudyrov]

I believe that the clutch or viscous coupling needs to lock up as it gets hot, I think that's the issue I had before my radiator blue up in traffic.
Unfortunately I don't have a direct test to share with you, however heres a great video that might help.

View: https://youtu.be/RDuGsDUiXQw?si=n78_-SYw3Rhi7TfU

 

[Pond]

I believe that the clutch or viscous coupling needs to lock up as it gets hot, I think that's the issue I had before my radiator blue up in traffic.
Unfortunately I don't have a direct test to share with you, however heres a great video that might help.

View: https://youtu.be/RDuGsDUiXQw?si=n78_-SYw3Rhi7TfU

Thanks. The video was very useful. It looks like I have fluid in the coupling and the bi-metallic strip looks all OK. It doesn't look like the rad is blocked or restricted (shone a torch through in various places).
I have a theory that because I have no engine trays fitted now, some of the air is travelling up the gap underneath on the fan side of the rad so fooling the strip on the viscous fan into thinking the air is cooler than it is.

Air will always find the path of least resistance. I shall test the theory with some towels.

 

[Eddie Zedder]

If it helps mine only kicks in when in stationary traffic on very hot days, you'll know when it does, it sounds like a freight train coming!

 

[ChrisD]

Thanks. The video was very useful. It looks like I have fluid in the coupling and the bi-metallic strip looks all OK. It doesn't look like the rad is blocked or restricted (shone a torch through in various places).
I have a theory that because I have no engine trays fitted now, some of the air is travelling up the gap underneath on the fan side of the rad so fooling the strip on the viscous fan into thinking the air is cooler than it is.

Air will always find the path of least resistance. I shall test the theory with some towels.

Can you not re-install your under trays? The overall powertrain heat management is designed taking into account the airflow paths created by these parts.

 

[Rudyrov]

Thanks. The video was very useful. It looks like I have fluid in the coupling and the bi-metallic strip looks all OK. It doesn't look like the rad is blocked or restricted (shone a torch through in various places).
I have a theory that because I have no engine trays fitted now, some of the air is travelling up the gap underneath on the fan side of the rad so fooling the strip on the viscous fan into thinking the air is cooler than it is.

Air will always find the path of least resistance. I shall test the theory with some towels.

Perhaps, you should remember that the thermal area that controls the fan clutch is in the center of the unit just a few inches behind the radiator.

 

[Duncodin]

Can you not re-install your under trays? The overall powertrain heat management is designed taking into account the airflow paths created by these parts.

I don't have the same rebody as Pond so I don't know what his is like but mine now has nothing to attach the front edge of the undertray to so I can't fit the front under tray even if I wanted to.

But my viscous fan comes on when it should.

When the engine is cold the fan is turning. It looks like it's spinning but it's just free wheeling. There's no power in it and I can stop it with my fingers. When the engine is hot and the fan is engaged i can hear the difference and, of course, I don't try to stop it with my fingers.

 

[Pond]

I don't have the same rebody as Pond so I don't know what his is like but mine now has nothing to attach the front edge of the undertray to so I can't fit the front under tray even if I wanted to.

But my viscous fan comes on when it should.

When the engine is cold the fan is turning. It looks like it's spinning but it's just free wheeling. There's no power in it and I can stop it with my fingers. When the engine is hot and the fan is engaged i can hear the difference and, of course, I don't try to stop it with my fingers.

I don't have anywhere to fit the tray, either.
When my engine is cold the viscous fan just 'ticks over', when the engine is hot it still just 'ticks over'. BUT...I noticed that my electric fan kicks in when the temp gauge reads around 100c. So I am wondering whether the electric fan is coming on before the viscous has a chance to speed up?

I don't want to change the coupling for it to do the same as it is now. All checks say the viscous fan should be OK. And the car isn't overheating, I am just not convinced it is operating quite correctly.

 

[ChrisD]

I think you’re right to be concerned and to ensure, as much as possible, things are working as they should. If you have a scan tool to read coolant temp and you feel brave enough you *could* run a short test with the electric fan disconnected. I understand that this seems to be stupid advice but I’d rather find out if the thing is faulty under controlled conditions rather than out in the wild.

 

[Duncodin]

The electric fan. Is that for the air con? My car doesn't have air con so I don't have an electric fan.

 

[Pond]

I think you’re right to be concerned and to ensure, as much as possible, things are working as they should. If you have a scan tool to read coolant temp and you feel brave enough you *could* run a short test with the electric fan disconnected. I understand that this seems to be stupid advice but I’d rather find out if the thing is faulty under controlled conditions rather than out in the wild.

Good idea about putting my scanner on to read the actual coolant temp, thanks. I hadn't thought of that. I have an aftermarket coolant gauge with the sensor in the drain plug of the block, so not convinced it is particularly accurate.
I had thought about disconnecting the electric fan, but would have to do that at the sensor on the radiator, as getting to the connector on the fan itself means a lot of work removing my front bumper, fog lights, grille, etc. It is not easy, then of course I have to put everything back!

 

[Pond]

The electric fan. Is that for the air con? My car doesn't have air con so I don't have an electric fan.

The electric fan is a dual purpose one. It it predominantly for the a/c but is used as an auxillary cooling fan aswell (triggered by a sensor in the radiator). My a/c is disconnected but the fan isn't.
Not sure whether it is engine-specific. Mine is a 3 litre M54, so will need more cooling than a smaller engine, presumably. But you would expect it has a larger radiator and larger viscous fan to cope with that.

 

[Duncodin]

Good idea about putting my scanner on to read the actual coolant temp, thanks. I hadn't thought of that. I have an aftermarket coolant gauge with the sensor in the drain plug of the block, so not convinced it is particularly accurate.
I had thought about disconnecting the electric fan, but would have to do that at the sensor on the radiator, as getting to the connector on the fan itself means a lot of work removing my front bumper, fog lights, grille, etc. It is not easy, then of course I have to put everything back!

This drain plug. Is that at the very bottom between the radiator and the block? The hottest place is the top of the block. ie best place to sense.

The cooling system on cars is "Pump assisted thermosyphon" meaning even without the pump the water would circulate (albeit not really fast enough) so, in the block the water gets hot and rises. In the radiator it cools and sinks. So water coming out of the radiator is coolest. So down there near the drain might not be a good place for a heat sensor. Maybe your water, at the top of the block, is much hotter than you think.

Does the electric fan have a dedicated fuse that you could pull out just for a test?


Going back to that term 'thermosyphon'. That's why really old cars had very tall radiators. They didn't have water pumps. They relied on the 'sinking' affect of water being cooled in a big rad to push the cooler water round the bottom hose into the bottom of the block pushing the hot water in the block out of the top into the radiator.

 

[Pond]

The hottest place is the top of the block. ie best place to sense.

Didn't have any choice with the location of the gauge sensor, other than drilling and tapping the engine somewhere (and I wasn't going to do that).
All other tappings have sensors which need to stay for one reason or another

I did actually study thermodynamics for three years as part of my HND in refrigeration. It was a very long time ago, though!

 

[Duncodin]

Here's a bodge

 

[Pond]

Here's a bodge

View attachment 349807

I know of someone who builds these cars and does theirs like that. It's more confusing that the legends are all in the wrong places and the "Chinglish".
I will be keeping mine as is. I will find out later how accurate my gauge is, as I'm going to run it with live data on the scanner.'

 

[Pond]

So I have run the car up to temperature again in my garage and put my scanner on it whilst doing so.
All temps are from my scanner (creator 410) but I don't know which sensor it takes the data from, the one in the radiator or the one under the intake manifold.

At 97c the viscous fan still just 'ticks over' but the electric aux fan kicks in. This runs until the temp drops to around 86c then stops. The viscous fan just keeps ticking over.
I would have expected the electric fan to cut in at a higher temperature (say 105c), but obviously don't know how accurate the scanner data is to the rad temps. I do know that the rad sensor is used by the electric fan.
I didn't disconnect the electric fan to see if the viscous would speed up, just in case the temps are not accurate.
So it looks like I am going to have to put a new viscous clutch in but am not convinced it will make any difference.

My gauge was showing around 8c higher than the data from the scanner, when it got to temp, BTW.

Inconclusive. That's what this has been.

 

[Duncodin]

. . .
It's more confusing that the legends are all in the wrong places and the "Chinglish".
. . .

Yeah. It's just a picture that google spat out. I noticed the legends but thought the picture was clear enough without leg ends.

It is quite a common mod used by people removing their belt driven fans and replacing with lectric.

 

[Nodzed]

I have a feeling my viscous fan on my M54 (3 litre) is not operating as it should. I have searched about this but am still confused.

So...here is my scenario....

My viscous fan runs from cold but doesn't seem to speed up (much) when the engine gets hot. It does alter it's speed but not by much. I tested it by putting a bit of white tape on one of the blades and watching it with a torch shining on it.

The engine gets to operating temperature (90c ish) then slowly gets hotter. All the time the viscous is running, but it doesn't change it's speed much at all (but does a bit).
When the engine gets just over 100c, the auxillary/ A/C electric fan kicks in and cools the engine back to 90c ish but the viscous doesn't change, it just keeps 'ticking over'.

I am not sure this is the way it is supposed to work. I was under the impression that the viscous should maintain temperature and the electric fan is only there if more cooling is needed that the viscous can't do when flat out.

Can someone please confirm whether my viscous is playing up, or this is normal with this engine?

If the viscous fan isn't controlling the temperature then it isn't functioning correctly end of! Get a new viscous clutch, they are not expensive and easy to change.