Fan clutch timing using an Iphone (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

TexFJ

SILVER Star
Joined
Jan 11, 2020
Threads
57
Messages
932
Location
Texas
Found a way to calculate my fan clutch speed using my iphone's slow mo speed.

70 degree day cold start had it at 60%.... sounds a little too much. Need to do it when the engine is warm, but I'm not sure if it'll change as the gauge never goes abofe 1/4


 
The speed of the fan in relation to the engine rpm is never constant. It's speed is changing all the time. Unless a person is a fan clutch engineer who has test data of rpms vs air flow vs radiator temperature vs engine temperature compared to other fan clutches, knowing the RPMs of the fan at some random moment in time isn't going to help identify whether the fan clutch us working properly or not.

The best way for us mere mortals to tell if the fan clutch is working properly or not is to look at a calendar. If the clutch is over ten years old it isn't working as well as it did when it was new. (That and the newspaper trick - and listening for a roar at startup and when it's hot).
 
The speed of the fan in relation to the engine rpm is never constant. It's speed is changing all the time. Unless a person is a fan clutch engineer who has test data of rpms vs air flow vs radiator temperature vs engine temperature compared to other fan clutches, knowing the RPMs of the fan at some random moment in time isn't going to help identify whether the fan clutch us working properly or not.

The best way for us mere mortals to tell if the fan clutch is working properly or not is to look at a calendar. If the clutch is over ten years old it isn't working as well as it did when it was new. (That and the newspaper trick - and listening for a roar at startup and when it's hot).
The normal operation for fan clutches, communicated by the fan clutch companies, has been Cold (20%-30%) and Hot (70%-90%). 60% at cold does seem to point to a start of an issue with the temp spring perhaps.

But we are mortals, as you stated. My investigation started due to a semi Roar.
 
A roaring fan clutch at first start of a cold engine is normal. The clutch works in a couple ways depending on where the silicon fluid is inside the clutch. YouTube has a couple good vids showing an illustration how it works. When the engine is stopped and cold, the fluid settles at the bottom. When it gets started up again, regardless of the temperature, the fluid will grab the clutch and make it spin until centrifugal force flings it out - disengaging the clutch. It's especially noticeable on really cold mornings because the fluid is more viscous and takes longer to flow.

If you're in doubt - replace it. I replaced mine after ten years not because I could definitively tell it wasn't working properly (it seemed ok) but just because it was "old" and I was refurbishing everything and got a new radiator. When I took the cruiser for a drive after the new fan clutch I could definitely tell the difference between it and the old one.
 
Last edited:
I notice mine on highway trips where I stop for gas a driving break. The fan roar always catches me by surprise as I accelerate down the onramp...and then it quiets down and I remember its there ;)
 
So I'm wondering the avg time from start for the viscous oil to be redistributed throughout the internals. I'm assuming this is when the roar goes away.
 
some years ago, I had my 61 only for a short time by then, I noticed that my clutch seems not to open at all. There was a constant slight howl from the fan.
Out of curiosity I opened the cluch carefully and found that the rotary valve which is operated by the bimetall spring was not closed on room temperature.
It seemed that the bimetall spring had gone a bit weak. I emptied the silicon fluid in a clean container and made myself a simple testing setup with a pot of water on a camping stove and a thermometer. I submerged the spring into the water and like this was able to watch the rotary valve working according to the water temperature. I think that I set the temperature at which the rotary valve starts to open at about 90°C or 194°F just to try it out. Reffilled the fluid fitted the two halfs back together....the cluch is just fine since then - that is about 50.000 km or 31.000 miles away. It howls after a cold start for about 500 meters or a third of a mile and on long uphills when the needle starts to creep up a bit - and cuts also out very noticeably when the rad temp has dropped enough. If you can't hear this action the clutch is quite likely always a bit on like mine was before. Or it´s not engaging at all - but then you would experience overheating in traffic jam or on uphills, and it would´nt howl when cold.
The engine feeled a lot free 'er and was quiter without the constant drag of the fan. I took some photo´s from the setup but unfortunately can´t access them now.
Just a thought to relax a bit from that unbelieveable c - virus around us all.
Stay healthy !
 
Last edited:
Found a way to calculate my fan clutch speed using my iphone's slow mo speed.

70 degree day cold start had it at 60%.... sounds a little too much. Need to do it when the engine is warm, but I'm not sure if it'll change as the gauge never goes abofe 1/4




Hey TexFJ, could you go into a bit more detail about how you are calculating fan speed? I see the tape on the fan and tge pulley, but im not clear how you figure out fan speed. Thanks
 
Hey TexFJ, could you go into a bit more detail about how you are calculating fan speed? I see the tape on the fan and tge pulley, but im not clear how you figure out fan speed. Thanks

I've slowed it down so I can count the number of rotations per a set time of the fan and then I divide it by the number of rotations of the pulley for the same set time. This gives me a % of the fan clutch spinning. I've read that during cold operation (assuming the fluid has already distributed) is normally around 20-30% of the pulley, hence spinning slow. Once the spring heats up it will allow for more coupling in the fan and the % will go up to 70-80% to blow more air through the radiator. It will never be 100%, if it is then it usually means that the fan clutch is bad.

Hope that explains my process.
 
I've slowed it down so I can count the number of rotations per a set time of the fan and then I divide it by the number of rotations of the pulley for the same set time. This gives me a % of the fan clutch spinning. I've read that during cold operation (assuming the fluid has already distributed) is normally around 20-30% of the pulley, hence spinning slow. Once the spring heats up it will allow for more coupling in the fan and the % will go up to 70-80% to blow more air through the radiator. It will never be 100%, if it is then it usually means that the fan clutch is bad.

Hope that explains my process.

Thanks TexFJ, that explains it. I haven’t done that test yet, but I think my fan clutch is pretty stiff even at cold temps. Lots of fan roar. It sounds like it might be an internal malfunction of the spring/ valve thing that regulates the temperature at which it kicks in. Wondering if this can be fixed?
 
Thanks TexFJ, that explains it. I haven’t done that test yet, but I think my fan clutch is pretty stiff even at cold temps. Lots of fan roar. It sounds like it might be an internal malfunction of the spring/ valve thing that regulates the temperature at which it kicks in. Wondering if this can be fixed?


Just remember to let the fluid work its way through on start up, this is what people are talking about when they say the roar. Initially after being still for so long fluid concentrates in one area of the clutch and it actually couples the fan. after a while it seeps into the other parts and then decouples until the spring gets hot and couples again to spin up faster.

refurbishing it is possible but messy, I'm assuming it's about cleaning it up and putting new fluid in. Also if your spring is the problem then you can't replace it and have to buy a new one... you could take it out and test it by heating up the spring with a hair dryer and see if that moves the spring and changes the way the fan spins.

I'd be sure it's really broken. if you think it's locked up, just make sure the fan spins with the engine off about 90 deg before stopping, if it doesn't budge then you have a problem and it's not the spring. If spins freely then you also have a problem and the fluid is prob gone.
 

Users who are viewing this thread

Back
Top Bottom