Fan hit radiator at high rpm

[Jim N.]

'69 L89 Duntov car. I decided to refresh the cooling system because my water pump was not correct and I suspected the fan clutch was not engaging. Found a Dec '68 rebuild water pump and purchased a new reproduction fan clutch from Zip. First drive I accelerated engine to about 6,000 rpm and promptly buried the fan in the radiator, broke the shroud (original), destroyed the fan, fan clutch, and radiator. I sent the water pump back to be checked out, bought a new reproduction radiator, fan and fan clutch. I assembled all IAW the AIM, ensured 1/2" clearance between the leading edge of the fan blade and the shroud mounting bolts and greater than .7" fan-shroud clearance all around the fan. First drive I accelerated engine to about 5,500 rpm and promptly buried the fan in the radiator - again. I have rechecked all the installation. There is a mark on the new shroud near the top mounting bolts which shows the fan hit the shroud. The only things common to these two accidents are the rebuilt water pump, the steel 5-blade fan, and the new shroud.
I need help figuring out what happened. The only thing I can think of is the fan clutch is not easing off at higher rpm, and the fan is actually bending forward to contact the shroud. Any thoughts?

[Larry M.]

Re: Fan hit radiator at high rpm

Motor mounts????

Larry

[Leif A.]

Re: Fan hit radiator at high rpm

Motor mounts????

Larry

My first thought, as well.

[Jim N.]

Re: Fan hit radiator at high rpm

My first thought, as well.

Sorry, I should have stated I replaced the motor mounts after the first incident. Looked at them after the second incident, and they look good.

[Joseph S.]

Re: Fan hit radiator at high rpm

The Waterpump should not be an issue. Your pulleys would not line up if it was out of spec. Did you measure the new fan clutch to the old fan clutch. Is the new shaft longer than the old one?

[Jim N.]

Re: Fan hit radiator at high rpm

I did not measure the old one, and unfortunately I threw it away. I think I did stand the two of them side by side, but I'm not sure. But when mounted, I was able to get a little over 1/2" clearance from the upper shroud mounting surface, and the one fan blade which remains in place still passes by that surface with about 1/2" clearance. If anyone has a measurement of the fan clutch shaft I would appreciate it.

[Mark Z.]

Re: Fan hit radiator at high rpm

Is a Feb70 ls5 clutch dtd 11 2 69 the same part?

[Jim N.]

Re: Fan hit radiator at high rpm

Is a Feb70 ls5 clutch dtd 11 2 69 the same part?

If your car has a date coded fan clutch then it's probably original - unless a restorer stamped a replacement. In my case the fan clutch in question is definitely an after market reproduction.

[Ed S.]

Re: Fan hit radiator at high rpm

If you suspect that the problem might be your after market repro clutch fan and can't validate its dimensions as compared to an original clutch fan and associated components I suggest you call KirkConnell - they specialize in restoring clutch fans, especially for Corvettes - good people - small shop - my guess is they will spend some time talking with you. They might be able to give you the dimensions for a correct fan clutch and associated components that you can compare to your hardware. Then you can verify that it or is not the fan & clutch that is the problem. http://www.kirkconnellcorvettes.com/.

And for what it is worth..... my 2 cents..... something is moving that should not be at high RPM or under load. Never heard of a fan clutch or fan stretching and then going back to its original shape when at rest.

[Dan B.]

Re: Fan hit radiator at high rpm

Did you remove any bolts from the radiator support? Give that a good check to rule out any possible movement.

[Joe L.]

Re: Fan hit radiator at high rpm

And for what it is worth..... my 2 cents..... something is moving that should not be at high RPM or under load. Never heard of a fan clutch or fan stretching and then going back to its original shape when at rest.

Ed-------

I TOTALLY agree!

[Jim N.]

Re: Fan hit radiator at high rpm

Dan, I actually removed the hood and pulled the radiator and the support out in order to install the new radiator. Used all new foam seals, so it took some pressure to get it all together. When I reinstalled it I tried to use all the slop in the holes to get as much clearance as possible, then tightened the bolts. Six side bolts and two bottom bolts. They were still tight after the most recent incident.

[Joe L.]

Re: Fan hit radiator at high rpm

'69 L89 Duntov car. I decided to refresh the cooling system because my water pump was not correct and I suspected the fan clutch was not engaging. Found a Dec '68 rebuild water pump and purchased a new reproduction fan clutch from Zip. First drive I accelerated engine to about 6,000 rpm and promptly buried the fan in the radiator, broke the shroud (original), destroyed the fan, fan clutch, and radiator. I sent the water pump back to be checked out, bought a new reproduction radiator, fan and fan clutch. I assembled all IAW the AIM, ensured 1/2" clearance between the leading edge of the fan blade and the shroud mounting bolts and greater than .7" fan-shroud clearance all around the fan. First drive I accelerated engine to about 5,500 rpm and promptly buried the fan in the radiator - again. I have rechecked all the installation. There is a mark on the new shroud near the top mounting bolts which shows the fan hit the shroud. The only things common to these two accidents are the rebuilt water pump, the steel 5-blade fan, and the new shroud.
I need help figuring out what happened. The only thing I can think of is the fan clutch is not easing off at higher rpm, and the fan is actually bending forward to contact the shroud. Any thoughts?

Jim------

A few thoughts: if the fan clutch were not "easing off" at higher RPM, that would be no different than a car with a direct drive fan and no fan clutch. Many of those were once built (and cars with original fan clutches so converted) and I never heard of one having your problem.

If the bearings in the fan clutch were bad enough to allow the fan to move enough to hit the shroud, that should be readily apparent by moving the attached fan by hand with the engine off.

I do not understand how the fan could move enough to contact and destroy the radiator unless something else moved significantly. An original fan is not going to "flex" enough under any circumstances I can think of.

Any deficiency that could result in what you describe and connected to the waterpump, fan clutch, or fan blade should be readily apparent with the engine off. As has been mentioned, it's not going to "correct itself" and appear normal with the engine off.

One thought: this all sounds like a motor mount problem. Many of the replacement motor mounts available today can appear OK but are of very low quality and can fail "from the get-go". Did you use original-style, non-locking mounts for the sake of originality? I absolutely DO NOT RECOMMEND the use of non-locking style mounts for ANY 1963-82 Corvette. What can occur is EXACTLY what you have described.

[Bill M.]

Re: Fan hit radiator at high rpm

Jim take a look at your transmission mount while you are looking at the motor mounts.

[Joe L.]

Re: Fan hit radiator at high rpm

Jim take a look at your transmission mount while you are looking at the motor mounts.

Bill-----

Yes, that's another possibility. In fact, in some circles the transmission mount is actually considered the rear motor mount. However, if a failed transmission mount does happen, if one has used LOCKING-STYLE side motor mounts, that will usually limit any "ensuing catastrophe" from a failed transmission mount. Another good reason to always use locking style side motor mounts regardless of originality.