How do fan clutches fail?

[Chris E.]

Just curious, when they fail, do they engage all the time such that the fan is running all the time regardless of temp or RPM?

[Gerard F.]

Re: How do fan clutches fail?

Chris,

I think it is the opposite.

The fluid leaks out and the fan doesn't turn fast enough when hot. The clutch slips too much when hot.

[Joe C.]

Re: How do fan clutches fail?

Just curious, when they fail, do they engage all the time such that the fan is running all the time regardless of temp or RPM?

A worn seal causes leakage which will deplete the working fluid, which will cause the device to freewheel if enough of the oil is lost. The fluid provides a viscous coupling.

[Jim D.]

Re: How do fan clutches fail?

How do you explain those that have too much resistance when cold with no signs of leakage?

[Joe C.]

Re: How do fan clutches fail?

Regulator valve sticky, and/or return channels restricted, causing fluid impairment in migrating back into reservoirs (the bulges that you see in the cover plate of the Eaton clutches).

The clutch operates by way of a restrictor plate whose size varies as the bimetal spring rotates the valve. As the bimetal heats, the valve rotates further, which allows a greater volume of fluid to circulate through the concentric circles of the clutch chamber. More fluid means more viscous shear. The fluid returns to the reservoirs through return channels.

[Chris E.]

Re: How do fan clutches fail?

So I saw a little fluid has leaked out of my original. I was going to clean it up and put it on the car for Regionals.

Given that I'll only be running the car for 10 - 20 minutes at a crack, am I in danger of hurting the engine with a fan clutch that might be worn a bit?

In my hands, the clutch still has a good deal of resistance. Anything else I should check for?

[Joe L.]

Re: How do fan clutches fail?

So I saw a little fluid has leaked out of my original. I was going to clean it up and put it on the car for Regionals.

Given that I'll only be running the car for 10 - 20 minutes at a crack, am I in danger of hurting the engine with a fan clutch that might be worn a bit?

In my hands, the clutch still has a good deal of resistance. Anything else I should check for?

Chris------


If you're only running the car for 10-20 minutes at a time, I don't think a weak fan clutch will be much of a problem. At 10 minutes, that's barely enough time to get the engine completely warmed up.

[Joe C.]

Re: How do fan clutches fail?

So I saw a little fluid has leaked out of my original. I was going to clean it up and put it on the car for Regionals.

Given that I'll only be running the car for 10 - 20 minutes at a crack, am I in danger of hurting the engine with a fan clutch that might be worn a bit?

In my hands, the clutch still has a good deal of resistance. Anything else I should check for?

The resistance felt after the clutch has been idle for awhile is meaningless, as the fluid seeks the lowest level. After the clutch has been rotating for awhile, a combination of centrifugal force on the fluid, valve position, and the return channels will establish an equilibrium point at which the oil is flowing at the proper rate to maintain demanded viscous shear. It is only at this point that a valid evaluation can be made.

You would be much better served by checking the condition of the bearing before you decide to use a "spare" fan clutch. Mount a fan to the clutch, hold the hub in a vise, or mount to water pump. There should be almost lateral NO movement when the fan blade is worked back and forth against the bearing. If the bearing is healthy, the chances are that your seal is intact also, albeit somewhat dry with age.

[Terry M.]

Re: How do fan clutches fail?

Just curious, when they fail, do they engage all the time such that the fan is running all the time regardless of temp or RPM?

Since yesterday was "Talk like Shakespeare day," I'll say: "Let me count the ways."

I had one that froze solid once. It took a while for me to notice it -- and no signs of leakage either.
I was a passenger in a Corvette with a fan clutch that came apart and exited through the hood. Kind of alarming in an L88 with M40.

[Joe C.]

Re: How do fan clutches fail?

Since yesterday was "Talk like Shakespeare day," I'll say: "Let me count the ways."

I had one that froze solid once. It took a while for me to notice it -- and no signs of leakage either.
I was a passenger in a Corvette with a fan clutch that came apart and exited through the hood. Kind of alarming in an L88 with M40.

Hi Terry. Actually, to be honest about this, I have to say Friends, Romans, countrymen, lend me your ears;I come to bury Caesar, not to praise him.The evil that men do lives after them;The good is oft interred with their bones;So let it be with Caesar. The noble Brutus Hath told you Caesar was ambitious:If it were so, it was a grievous fault,And grievously hath Caesar answer'd it.Here, under leave of Brutus and the rest -For Brutus is an honourable man;So are they all, all honourable men -Come I to speak in Caesar's funeral.He was my friend, faithful and just to me:But Brutus says he was ambitious;And Brutus is an honourable man.He hath brought many captives home to Rome Whose ransoms did the general coffers fillid this in Caesar seem ambitious? When that the poor have cried, Caesar hath wept:Ambition should be made of sterner stuff:Yet Brutus says he was ambitious;And Brutus is an honourable man.You all did see that on the Lupercal. I thrice presented him a kingly crown,Which he did thrice refuse: was this ambition? Yet Brutus says he was ambitious;And, sure, he is an honourable man.I speak not to disprove what Brutus spoke,But here I am to speak what I do know.You all did love him once, not without cause:What cause withholds you then, to mourn for him? O judgment! thou art fled to brutish beasts,And men have lost their reason. Bear with me;My heart is in the coffin there with Caesar,And I must pause till it come back to me.

Now, that being said, when the fan exits the way that you describe, and as long as it clears the radiator, it creates an auxilliary cooling hole in the hood, which is quite effective................

[Peter J.]

Re: How do fan clutches fail?

Chris,
When I first bought my 66, it ran hot and I knew a guy who had been running a radiator repair shop for at least twenty years. His test for a fan clutch was to put on a leather work glove and see if he could stop it while the engine was idling. Mine stopped without much resistance and that was his diagnosis. I replaced the original with an Eaton copy that was close but not perfect. And problem solved.
Pete

[Gerard F.]

Re: How do fan clutches fail?

The resistance felt after the clutch has been idle for awhile is meaningless, as the fluid seeks the lowest level. After the clutch has been rotating for awhile, a combination of centrifugal force on the fluid, valve position, and the return channels will establish an equilibrium point at which the oil is flowing at the proper rate to maintain demanded viscous shear. It is only at this point that a valid evaluation can be made.

You would be much better served by checking the condition of the bearing before you decide to use a "spare" fan clutch. Mount a fan to the clutch, hold the hub in a vise, or mount to water pump. There should be almost lateral NO movement when the fan blade is worked back and forth against the bearing. If the bearing is healthy, the chances are that your seal is intact also, albeit somewhat dry with age.

Guisseppi,

Is there any procedural test for the fan clutch. How did the manufacturer test these clutches before they out them on the car, or are there any on the car tests for the dealers service shop.

Don't see anything in the service manual.

[Joe C.]

Re: How do fan clutches fail?

Guisseppi,

Is there any procedural test for the fan clutch. How did the manufacturer test these clutches before they out them on the car, or are there any on the car tests for the dealers service shop.

Don't see anything in the service manual.

As we all know, Gerardo, everybody has his own favorite test procedure............including those in which the victim, er, Tester's Apprentice (aka: testis) risks losing fingers in endeavouring to find out whether the fan blade will stop rotating...............................or not.

Even "Mister O" suggested my using one of the more popular tests to quickly determine if the device was stone dead or not, but you are skeptical as to its validity in determining a useful performance profile? Nothing in writing AFAIK. Give Eaton a call, inform them that you're an Engineer, and that you're doing a "white paper" on Corvette overtemperature issues. They should be able to come up with their test procedure.

Giuseppe

[Jack H.]

Re: How do fan clutches fail?

The performance profile of the clutch is guaranteed by design and the control of its constituent parts, Gerry. It's a rather complex curvalinear plane in 3-space.

One axis is RPM, the second is temperature and the third is %-slip. First, you need the design spec from either Eaton or Schwitzer. Then, you mount the fan clutch to it's specified load for proper drag (the fan PN that's called out in the fan clutch drawing/spec).

Now, you spin the input shaft using a stroboscope to verify RPM and move the stroboscope to the body of the fan clutch to get a second RPM reading. The difference in RPM is then translated into %-slip.

Do this across the RPM axis. Then, repeat the test varying temperature and making SURE you've allowed thermal equilibrium to take hold before each delta-T reading and %-slip calculation.

Finally, compare the two sets of numbers to the fan clutch drawing specification. The test is a time and instrumentation consuming B(*&^ to do! The only guy I know who fabricated a controlled environment to properly characterize fan clutch operation is Fred Oliva.

On the 'hand' method of determining good/bad, you may be able to spot a complete 'basket case' failure. But, there's no way you'll be able to verify full pass/fail conformance to spec by hand!

WAY back when, Fred Oliva put on a tech session and provided about eight fan clutches. He invited members from the audience who thought they could tell good from bad by hand to come forward and sort the eight fan clutches.

Bottom line NOBODY got it right!!! Turned out all of the samples were out of spec in one form or another...

[Jim V.]

Re: How do fan clutches fail?

Chris,
When I first bought my 66, it ran hot and I knew a guy who had been running a radiator repair shop for at least twenty years. His test for a fan clutch was to put on a leather work glove and see if he could stop it while the engine was idling. Mine stopped without much resistance and that was his diagnosis. I replaced the original with an Eaton copy that was close but not perfect. And problem solved.
Pete

Hmmm...how many hands did he have left?