Ok, yesterday's topic was a bit much... so today I got a simple one! :)

Lets talk about our stock fan/fan clutch. Paul brought up a good point about how his stock fan performs compared to the 16" Spal. Personally I'm surprised (I thought the spal moved a lot of air)... but then again, I think my fan clutch is dead.

Anyone want to talk about how it works, how the oil within the clutch controls the speed of the fan at varying tempratures, etc? Also... I wonder what type of CFM this thing puts out... and is there even a NEED for a Fan delete when you consider that if the water is cool.... the clutch slips... when it's hot the clutch engages. What kind of hp gains are you REALLY getting if any?

Anyone? :D

Boris

Good Topic, Boris. Ive been doing alot of fan clutch research in the last 24 hrs, cause I find its a subject many of us dont know too much about.

The clutch is the metal round thing thats riveted or screwed, in 3 places I believe on the stock M3 fan (4 places I believe on the smaller 318 fan, although that could be backwards) to the fan itself. And its a trickly little mechanism... You can buy them for anywhere from about $160, all the way down to $89 for the Sachs oe one. Those are all net prices.. Dont know what the dealer charges, but theres no need to go there.

So, anyway, the clutch has a chamber thats filled with silicone oil.. There is a bimetal piece which expands with heat.. As it expands, it opens a chamber into which the oil flows. Its this flow of the oil internally which regulates how much the fan 'freewheels', or how much it 'stick's, to really move the air. When the fan is cold, ie, after the car has been parked overnight, if you open the hood, and manually spin the fan, a good fan clutch should feel like its fluid damped when cold like this. You should feel a damped resistance, and it should NOT free wheel. It should NOT continue spinning after you take your hand off the fan. I found that my 318 fan and clutch which Id been driving for 50k miles felt MUCH loser than did the M3 fan and clutch, when cold. Now, dont be mislead.. If youve driven the car for several minutes, and its started to warm up, perhaps to 185 - 190 degrees on the coolant temp sensor, and turn the car off, and spin the blades, it WILL free wheel... Thats ok.. Its supposed to do that. It allows the engine to not be robbed of HP when you dont need the fan to cool things off. However, if you park, and idle the car for several minutes, and even step on the gas to maybe 1500-2000 rpms, and watch the coolant temp sensor rise over 200, you WILL reach a point when the fan clutch 'engages'.. You will know when this happens, because as you give it throttle, eventually, you will hear a Loud Whiny Roar, indicating the clutch is now engaging.. And its NOW that the thing is Really moving the air!!! And its now, if you turn the engine off, that you will feel good resistance to manually turning the blades. Its at this point, and when its completely cold, when you will be feeling the fluid damped resistance if the thing is working properly.. .When its hot enough, you can Also hear the telltale roar when you accelerate in like first gear.. its unmistakeable.. It reminds me a bit of a jet engine's whiney roar. Its way cool, and its what you want to hear if youre running the oe fan.. How much air does it move? We never see a cfm rating because a cfm rating is only given for fans which have some constant factors the fan clutch doesnt have, since its dependant to a degree on engine rpm. But, Ive seen on other applications, like on a chevy truck forum, that their mechanical fan was worth 5000 cfms.. I wouldnt be at all surprised if, on ours, the thing didnt put out at least 3200 cfms when engaged, or about twice the midrange 16" spal. But if youre going to do this manual test by feel, at idle, make sure its warmed up enough to create that 'Roar' indicating its been engaged. If you try to feel the air movment before this happens, you wont get a true indication of its capacity.

Interestingly, there is another type of mechanical fan arrangement called a Flex-a-lite, or something like that. .Instead of a fan clutch it works on the principle of blade flexion. Under certain conditions, the blades are designed to 'Flex' so as to go flat, and not move the air; kind of like the freewheeling of our fan clutch before it engages. That allows the engine to not be dragged down at all. Ive read that its These flexlite types of fans which alot of dragsters are using, as it seems that they are capable of really moving a ton of air. It is possible to adapt them to our cars, by applying the proper spacers, avaialable from flexalite dealers. Of course, Ive also read that, in conditions where every thousandth of a second counts, sometimes electrical fans will be used, for their complete lack of engine drag.. However, lets not forget that it takes power to make power. The drag on the alternator of a hi performance electrical fan has to be taken into consideration, as an engine dragging factor.

So, thats about the state of my research to date, and Ive found the whole topic very interesting. I think its very valid for this forum, because so many FI people are having to deal with heating issues all the time due to the extra power their engines are being asked to produce.

I knew you'd be the first to post, Paul :D. Anyway... that's great info.

It's amazing how clever this thing is designed. I didn't even realize (until recently) that the clutch is temperature sensitive at all. I'm sure others didn't know that either... which is why I wanted to start this thread. Many people think they need to get a SPAL to move more air, when in reality the stock fan can probably even do a better job if the fan clutch is doing its job!

Now... as long as nobody debates your description of the fans operation... I'd like to also discuss the "Fan Delete Mod." Since the thought is that the fan delete "frees up" the energy that would otherwise be used to power the fan... it looks like that is not the case when the clutch is disengaged.

Here's what I'm interested in: is this clutch an ON/OFF type? Or is it "infinitely variable." Also, is it possible to calculate the power loss when the clutch is disengaged? In other words: when it's taking the least power out of the engine?

It would be interesting if in your next dyno run you took a wrench with you (and if you can get consistant runs) remove the fan clutch on one of the runs to see the difference in power. Has anyone done this (even N/A?).

Boris

>>Here's what I'm interested in: is this clutch an ON/OFF type? Or is it "infinitely variable<<

Its definitely Variable.. there are degrees of engagement!!

>>when it's taking the least power out of the engine<<

When its most freewheeling! ie, when the oil has entered the engagement chamber the least.. which happens when the engine is running, but coldest. Like when youre driving along on the freeway, with plenty of flow, at 60mph or more, with coolant temp sensor reading in the 170s-180s. I would think that in the 190s approaching 200, its in the transition zone.. and Id think that above 205, its approaching full engagement. These are not accurate, but Id bet that, on our cars, from looking at the temp sensor readings, while noting fan sounds and feel, theyre not too far off.

It doesn't surprise me in the least that a stock mechanical fan can outperform an aftermarket electric fan. OEM fans are designed (engineered) to be reliable and provide cooling under the most extreme conditions. You'll be hard pressed to improve upon it.

>>If youve driven the car for several minutes, and its started to warm up, perhaps to 185 - 190 degrees on the coolant temp sensor, and turn the car off, and spin the blades, it WILL free wheel... Thats ok.. Its supposed to do that. It allows the engine to not be robbed of HP when you dont need the fan to cool things off. However, if you park, and idle the car for several minutes, and even step on the gas to maybe 1500-2000 rpms, and watch the coolant temp sensor rise over 200, you WILL reach a point when the fan clutch 'engages'<<

I think I may have mislead here, because I quoted approximate coolant temp sensor readings, and linked them to the degree of 'sticktion' of the fan clutch.. In reality, the fan clutch has no way of 'knowing' what the temperature in the head is.. What its really responding to is the temperature in the engine bay, in the vicinity of the fan. Now, consider the discussions weve had relative to the removal of the underhood weather stripping.. I think we found that most of the cooling which resulted occurred at the other end of the engine bay. But, if we are only running one fan, and its the mechanical one, like those of us who have removed the aux fan because of the aftercooler heat exchanger, and are using the OE fan instead of the spal, I would be very careful about doing anything now which would delay the engagement point of the fan clutch.. Same thing might apply to the ommission of the underpanel. To the extent that the engine bay is cooled, the engagement of the clutch will be delayed. Now, if that cooling really helped lower the coolant temperature, Id be all for it.. But I dont think it does. Therefore, tomorrow, back goes the weather stripping! I dont know if its the 'right' thing to do, but it seems to make sense, at least in my application

Paul, I think you should be fine. Weather stripping removal really helps with speed. I bet the temperature around the fan is approximately the same with or without the stripping. I could be wrong... but just a thought.

Also, I would think that the clutch would get it's heat from the water pump bolt, seeing as all that hardware in the water pump is directly connected and the metal conducts the heat to the clutch. Does that make sense? What does the TIS say about the fan clutch?

Also, anyone know if this is a normal "change" item as it seems to go bad after some time? Any word in the Bentley on how often it should be replaced, etc?

Thanks,

Boris

>>. Weather stripping removal really helps with speed<<

Ok.. good point.. we dont need the fan when were pulling air in via the cowl... thats when it should be most likely to be freewheeling anyway.. And when we are in traffic, no air is being pulled through the cowl anyway, so temps will be allowed to build, aiding in fan clutch engagement.

As for replacement intervals, Ive got the 318 fan on which I think the clutch may still not be totally dead, but its definitely softer than the one on the 6k mile M3 fan clutch, and youve got somewhere in the mid 40k useage, and yours is soft also.. So maybe a good guess might be to replace somewhere in the 45-60kmile period. According to bentley i can find no replacement interval.. but they do say that so long as there is at least Some resistance with the car cold, engine off, the clutch is still useful.. Only when it completely freewheels when cold, with no resistance, is replacement neccessary. Ill do some more searching tonight, and see if elsewhere on the net, I can find any data about failure rates/intervals, etc..
I too was thinking that perhaps, its leaching some heat from the waterpump shaft on which its mounted, although I dont know for sure.

So what water temps are you guys seeing in normal day to day driving?
Also please state if your F/I application is water cooled.
THanks,
Pedro.

Im seeing coolant temps while cruising, 85 degrees ambient, in the low 190s. With AC on, that will generally hover between 199 and 203. Thats with the oe M3 fan only. When I had replaced that with a spal 16" midrange, I found these temps to be generally about 10 degrees higher.