Sorry for the double post. Putting it here also as the Heating/Cooling forum gets less traffic.

Hey guys,

I recently pulled a 454 from the junkyard and of course, it has a big block clutch fan.

The rest of the BBC set up is going into my brother's Nova.

I was thinking of using the clutch fan on my malibu to replace the flext fan it has now.

My only problem is finding a non-thermal clutch. We pulled the engine from a 77 Suburban, and there's no PN for a non-thermal clutch for that application.

I've found the following part numbers, in case anyone knows how to read part numbers for replacement clutches.

215049 - 1970 Chevelle THERMAL
215045 - 1977 Suburban THERMAL
211049 - 1970 Chevelle CENTRIFUGAL

These are all #s for Imperial parts.

4949- 1970 Chevelle CENTRIFUGAL
4849- 1970 Chevelle THERMAL
4845- 1977 Suburban THERMAL

These #s are for Ready Aire parts.

I can already see that 49 and 45 are specific to the vehicles, but I don't know what they mean as far as fitting.

Why would their be a difference?

Bump.

Anyone know if all BB fans are similar enough so that you can swap a clutch from one to the other?

I researched a little and it seems the truck fan cluthes pushed the fan farther foward or something?

Why would you not want a thermal fan clutch? My impression is that a non-thermal clutch is designed for people who won't spend the money for the "right" part. It's a cheap-to-make compromise that doesn't really do the intended job. Am I missing something?

Be sure the fan will fit your shroud.

The different part numbers "probably" refer to different distances from the fan mounting surface to the water pump flange--the height of the fan clutch. Another difference is the size of the clutch itself. The heavy duty ones are bigger.

If you go to:
http://www.haydenauto.com/assets/2003Haydencat.pdf
and scroll down some, you'll find a dimentional chart that could be of help.

you will get better cooling from a mechanical fan by far ditch the clutch

fan blades will inter-change from different clutch fan assy's. i just went thru this while ago on my bbc z28.

jmo but a mechanical fan is the band-aid for the folks who are trying to cover up other cooling system problems, with fan shroud and a good clutch fan.....with proper size radiator that is a very good set up to cool about any engine.....

i myself run a clutch fan, fan shround and 3 row radiator in my 80 z28 bbc and it keeps it very cool.....and the added bonus is there is less hp draw using a clutch sytle fan...then a fixed mechanical fan......

The only reason I'm looking towards using a Centrifugal/Viscous set up is that I read an earlier post by Bomber 67 about "freak" accidents where a thermal clutch will suddenly engage on the back half of the track and since it was never designed to engage at such high rpms, the fan would get tossed through the radiator.

Sounds like some expensive carnage to me. My car runs relatively cool, 180-190, 200-210 on a very hot summer day in stop/go traffic. But I've also heard horror stories about flex fans coming off at high rpm and trashing shrouds/hoods and fuel lines. The fact that I have to be under the hood revving the engine to check the timing curve, is enough to scare me just thinking about the fan coming off AT ALL while I'm close to it.

29.95 Flexalite non-thermal clutch fan in Summit, its what I'm using.

Enrique, I have blown fans through radiators and all manner of parts while drag racing - but I think you misread my past posts on fan clutches. I do believe in fan clutches for most street/strip applications over any fixed fan, and I do prefer simple viscous fan clutches. That said I've never seen a thermal clutch "suddenly" engage at high rpm. By the way, the one time I had a fan fly into the radiator it was because of a Weiand pump that was mis-machined on hub to shaft interference fit.

Motown, everybody has their own set of knowledge - but your fixed fan is slowing you down. Or if you use an itsy bitsy blade fixed fan then you will not have good street rpm airflow through your radiator. Everything is a compromise, choose wisely for your use.

Thomas

Hi Thomas, sorry for misreading your posts.

Now, why is it that you like a viscous cluth over a thermal? Does the viscous still have a power advantage over the fixed flex fan?

By the way, how does a viscous clutch work?

I know on the thermal they have a little coil in the front that "grows" much like the choke mechanism inside my holley's electric choke. And some how that engages/disengages the fan at certain temps?

Almost anything will have a power advantage over a fixed fan - a fixed fan is always engaged no matter what the engine rpm. Flex fans offer little power benefit over rigid fan blades. A viscous coupler "de-clutches" limiting output rpm at high engine rpm. A thermal clutch is great for trailering applications where underhood temperatures get toasty and you can have higher rpms for slower speeds (down a gear while ascending a grade). The thermal clutch senses this and keeps the fan more engaged to increase airflow.

Oh yeah, what about electric fans? They definitely have their place, but consider: two good fans at 25 amps draw apiece means the alternator has to be fairly high output to cover the fans, stereo, and everything else. A 100+ amp alternator uses considerably more hp to spin than any 50 amp alternator. So, although electic fans don't directly take engine power to spin, by default the increased alternator hp draw probably exceeds the power benefit of not having the fan engine driven.

Thomas

Thanks a lot Thomas.

Thanks Robert, and if you don't mind, what fan/shroud are you using? You don't happen to be using a Suburban/Truck BBC fan with a Chevelle shroud?

Schurkey, thanks for the link, I just noticed it.

I removed the shroud when I went with the AFCO aluminum radiator and it runs just as cool without a shroud as it did before with a shroud. I was using the original smallblock shroud before the radiator change. I like the aluminum radiator,cools down(dissipates heat quicker) between rounds.

Thanks,
What fan are you using?

Nevermind, in your first post you stated it was a Flexalite fan.

Stock G.M. 7 blade fan with a flexalite fan clutch.

Centrifugal is non thermal.

Leo, thanks, I knew that already though. The issue was that there's no PN for a Centrifugal/nonthermal for the Suburban application, which is what I wanted to find since this is a fan set-up from a suburban.

But I'm thinking I can get away with using the Centrifugal/nonthermal part spec'd for the 1970 Chevelle/Malibu 402/454.

I run a seven blade clutch fan with a non thermal clutch as well.Thats all I ever used on any of big block cars over the years..never had a problem running hot,even with a 3 core and 10.50 to 1 compression.
Ever see a flex fan go thru a hood?

Originally posted by Slowpoke70:
But I'm thinking I can get away with using the Centrifugal/nonthermal part spec'd for the 1970 Chevelle/Malibu 402/454. ..that will work fine.

What brand of thermal clutch do you guys reccomend and where to buy ??

Thanks

Originally posted by CDN SS:
What brand of thermal clutch do you guys reccomend and where to buy ??

Thanks anyone???

The ones I run on my cars I get from Pep Boys..less than $30 each..and I've never had a problem..bought about half dozen over the years between my own cars and project cars.
Can't remember the name brand though graemlins/clonk.gif

I'd like to toss something in here. If you buy a new parts store thermal fan clutch, and plan on using it on an engine break-in, don't. Found this out the hard way. The fan clutch needs to sit vertical for a day or two before it'll work properly. As it sits around on a parts shelf, the fluid works it's way away from the portion where it works best, the edge of the housing. If you plan on using one, sit it on edge, as it would sit installed, for a couple of days. Tossing one on your car and daily driving it shouldn't be a problem, as you're getting airflow from the car moving.

And those of you with flex fans on your daily drivers, you should inspect them when you change oil. I pitched a blade on my '79 K10, not turning over 3k. Found 2 more blades ready to go. Luckily, it went straight out the bottom of the shroud. Bounced off the truck/road a couple of times after it got out.

My car is only a small block, but the stock GM clutch fan, shroud, and 3-row radiator has never let me down, even in extended periods of idling in 90 degree heat. While driving from Atlanta to Nashville for Chevellabration 2003, I got stuck in traffic on the interstate for nearly two hours to go one mile, on a pretty hot day. Water temp never went over 185. The stock fans are much quieter also. For a car that sees mostly street duty, I think the GM clutch fan is the way to go.

A guy was struck in the chest and killed by a flex fan blade while setting the timing on his bracket car at IRP a few years ago.

=( Thats the scariest thing ive heard in a long while. I see the importance of shrouds in a whole new light! I will be installing a new fan assembly to the 454 build this week. Not sure what I will run either, I just want something simple and cheap for a somewhat mean daily driver =) Id like to try a non-clutch fan, doesnt sound like too many people are fond of em'

Phil, the shroud isn't going to do jack to save your life if a flex fan lets go while you're under the hood. Think about it, these things put dents into hoods and cut through trans lines, the plastic shroud will hardly slow it down enough to save your life.

Dang, now I don't feel like doing any tuning until I toss that fan out and buy a good clutch for the BB fan.

Enrique, just give it a good inspection. Check for cracks, loose rivets, etc. They're safe as long as they're sound. I've run them for close to 20 years, never had a problem until a couple years ago. Of course, that truck is basically neglected because it's so reliable, that's why I missed it. BTW, there's still a nice hole in the bottom of the shroud to remind me to check the fan once in awhile.

Im am totally convinced to go with a clutch style fan =) phew...

Darren, true, I'll check it on Thursday if I go race. But since I already have the BB fan and components to mount it, all I need is a clutch and I'm ready to do the swap.

Go with a HD thermal fan clutch. They will cost about 60 bucks versus the elcheapo ones at any auto parts store that and a stock GM 7 blade fan should cool anything if the rest of the system is ok.

What Greg said. Get up off the extra $30 or so bux, run a quality thermal fan clutch. Best thing there is. Those aluminum flex fans, think about what it's like at RPM when the blades flatten out: like a round piece of plywood bolted on there. I've spent years learning this stuff running dirt cars in Phoenix in the summer.

I was almost killed by a pitched aluminum flex fan blade once, I was leaning over the front winging the thottle checking the timing at RPM. I went around the side and hit it again, the blade went through where my head was just a few seconds earlier. It would have cut my head off. Never again, that was too close, I can take a hint. Besides, think of the humiliation, it was a F0rd. Killed by a F0rd? Please.....

Tom