[craiglemans]

Guys, thanks for all the help in tracking down this issue!!! I have been dealing with a cooling issue for a while and I never put 2 and 2 together until I read some posts on this site. About 4 years ago, I "upgraded" from my old flex fan to a 6 blade clutch fan. Immediatly the car ran much warm and I put a new HD clutch on it from advance auto. since then, I've been tracking down other issues and never thought much about it.

I drove the car to Syracuse Nationals this past weekend and the temps climbed up to 225 on the highway. After reading some links on this site I figured I would give my old flex fan a try. Turns out my old flex fan is a 7 blade 19" bohemoth. Not sure what it was off (it came on the car when I bought it), but looks similar to some caddy fans that I've seen on ebay.

With my old flex fan, the car now stays @ 180 on the highway and seems to stabilize around 195 at lights and then goes back down to 180 once I start moving again. So, it turns out that the flex was the silver bullet for my cooling issue!!!

For the record, I'm not saying all clutch fans are bad, I just had a low quality clutch that ended up over-riding my t-stat. Without this site I never would have figure this out. thanks again guys!!!

[lust4speed]

You have to be fair in your comparisions. The largest stock clutch fan is 19.5" and has seven blades. I've run both the HD clutch with the 19.5" fan, and the 19" 7 blade flex fan. It was pretty much a draw between the two on which was the absolute best for cooling, but the flex fan noise was too much for me and I went back to the clutch setup.

[Rugratman]

Are you running a spacer on the flex fan?
If not, it should help also.

[Z Code 400]

18" 7 Blade Flex Fan and 2.50" spacer ran 30° cooler on my car (+100°F ambient) than any combination of 18" and 19" 5 and 7 blade fans and Severe Duty clutches...Robert

[Z Code 400]

http://forums.maxperformanceinc.com/...d.php?t=563796

[JSchmitz]

I've ran all different kinds of flex fans over the years. None of them cooled as well as a clutch fan. They didn't even cool as well as a GOOD heavy duty clutch. A severe duty clutch will about pull the grill through the radiator. The key is getting a good clutch. I use Hayden clutches with great success. Using some old, used up, p.o.s. clutch is not a good measure for comparison. What kind of fan do they run on heavy duty trucks, etc.? A clutch fan. There's a reason.

[Z Code 400]

My 7 blade, 18" Lincoln Flex Fan outperforms every clutch (Hayden, 4 Seasons, Ever-Kool and Torq-Flo) with every fan (5 and 7 blade) that I have ever used and is much, much quieter.

While it is true, the SD clutch will pull a lot of air WHEN applied, it pulls almost NOTHING when it is freewheeling. It is during this freewheeling period that the temperatures creep up.

It's hard to compare HD trucks to our Pontiacs. Look at the Pontiac service manual for some clues: "A 5-blade Power-Flex fan is used in Police and Taxi applications when maximum cooling is required..."

Now, my 1985 Suburban has a thermostatic clutch and came from the factory with a 19.0", 5 blade fan. I replaced this with a 19" 7 blade fan and it works very nicely. It never gets over 200°F and runs about 175°-180° @ 70 mph with the A/C on in +100°F ambient temperatures. However, during long periods of idling, the temperature creeps up to 200°F, while the fan is freewheeling.

Just as an experiment, I threw my 7 blade Lincoln fan on there and it never got over 185°F, regardless of idling, load or ambient temperatures.

Keep in mind that some engine produce much more heat than others too.

The best fan out there is the rolled-edge, 18.0" 7-Blade Pontiac Flex Fan that came on Grandville's and Safari Wagons with the 455 engine. They bear part number 3998988...Robert

[JSchmitz]

Originally Posted by Z Code 400

While it is true, the SD clutch will pull a lot of air WHEN applied, it pulls almost NOTHING when it is freewheeling. It is during this freewheeling period that the temperatures creep up.

Thermostatically controlled fan clutches only "freewheel" when the incoming air temperature is low enough to disengage the clutch. This means it doesn't need to be pulling air. That's the whole point. Clutches also limit the fan speed to a percentage of the water pump speed. Flex fans don't. I know they are supposed to flatten out. I just have never seen one pull a lot of air (without a lot of drag).

Originally Posted by Z Code 400

It's hard to compare HD trucks to our Pontiacs.

No, it isn't. Any engine with a high cooling demand will benefit from a good fan. The fan/clutch doesn't know what label is on the heat producer. My point was, That the oem's choose clutch fans for vehicles with a high cooling demands. Maybe you should call and straighten them out.

I'm not saying flex fans are junk. I ran a plastic one for years with good success. I've also ran several kinds of aftermarket, and factory, metal flex fans. None of them held a candle to a good clutch.

I think a lot of people try an old p.o.s. clutch that's leaked half the oil out. Then they claim clutches don't work.

[Nomadac]

My experience with Flex fans vs. Clutch fans has been on a 55 Chevy Nomad. Both the 283 c.i. engine and then a 383 stroker motor had cooling problems when sitting in traffic and high ambient temps. I tried numerous flex fans stainless and fixed blade aluminum. Then I relocated the radiator to the front of the core support so I could install a shroud. I added a HD Fan clutch from Flex-a-lite and there 6 blade clutch 17" fan and my cooling problems were solved.

My 83 GMC Suburban 2500 7.4 L has a 7 blade clutch fan that appears to be somewhat of a flex type blade. My 2001 Chevy Suburban 8.1L has a 5 blade steel clutch fan and both vehicles have been used for trailer towing and never experienced a cooling problem or ever overheating even in long hill climbs pulling a 7600# TT.

My point being the clutch fans when used in HD applications and high temps. seem to provide more air flow at lower speeds or traffic when the outside temps. are in the 90's and under a load.

My current 63 GP has a 6 blade flex fan with spacer and shroud and does not seem to move the air that the same fan I used on my Nomad. I am looking for a 19" clutch fan and have a clutch for a Pontiac I will install. I am currently looking at a 7 blade clutch fan that fits:
67-68 Z28
69 w/ A/C & A.T.
69 396 w/A/C Fan Drive
69 w/o A/C Fan Drive
70 350 or 396
I have not been able to receive a reply as to the bolt pattern measurements and if it will exchange with the Fan Clutch for a Pontiac. If so this seems to be the answer, as it is supposed to be made to OEM standards of quality. Does anyone know if a Chevy Fan will work on a Pontiac?

[Z Code 400]

Originally Posted by JSchmitz

"I think a lot of people try an old p.o.s. clutch that's leaked half the oil out. Then they claim clutches don't work...."

I have used several of them from a number of different companies (Hayden, 4 Seasons, Torq-Flo, AC Delco)and none of them cool as well as a flex or solid fan and for the record, the factory fans are much quieter and offer more airflow than the aftermarket flex/solid fans....Period.

Originally Posted by JSchmitz

"Any engine with a high cooling demand will benefit from a good fan. The fan/clutch doesn't know what label is on the heat producer. My point was, That the oem's choose clutch fans for vehicles with a high cooling demands. Maybe you should call and straighten them out...."

I agree. But, perhaps you would like to refer to the 1975 Pontiac Service Manual for their description of the 5 Blade Power-Flex Fan:

"Police and Taxi packages are equipped with the 5 blade Power-Flex Fan where maximum cooling is required. The blades flatten out to a near zero pitch at or near 5,000 rpm."

Funny....I have seen several Safari Wagons with the trailer towing package that came equipped with the #3998988 18.0" 7 Blade Flex Fan.

Maybe you better call Pontiac and tell them a clutch would work better...Robert

[Z Code 400]

Originally Posted by Nomadac

"I have not been able to receive a reply as to the bolt pattern measurements and if it will exchange with the Fan Clutch for a Pontiac. If so this seems to be the answer, as it is supposed to be made to OEM standards of quality. Does anyone know if a Chevy Fan will work on a Pontiac???"

All the GM fans I have worked with have the same pattern...Robert

[Region Warrior]

I've had good success with both last 30 yrs(19.5" and 50/50 into shroud).
But never had to replace a water pump using flex fans...yet.

[70 Lemans]

I hate to hijack this thread but my info is relevant,

Long story short,

Day one running 16deg initial timing with 33 deg total. Running 200 degrees. I changed nothing but the clutch fan Hayden 2797. I ran it for 45 min with it never getting over 162 deg. Actually it’s kind of scary how cool this thing is running, I actually almost blew off the air cleaner cover when I REV’ED it.

Ill be making a spacer to bring thermostat spring closer to radiator by 1 inch.

We will see what happens

When will it desingage?

Steve

[Z Code 400]

Steve,

The spacer is not reliable with a clutch. Use a longer clutch, like the one used on the V6 Buicks...Robert

[sixt8bird]

I have to agree with the flex fan cooling better. At least on my car. I swapped a couple clutch fans on my car that I race and the temps hovered around 200 when the flex fan would never climb above 175. Im sticking with the factory power flex fan.

[70 Lemans]

I was thinkng billet aluminum. I have acess to a lathe. Will this be ok. Could even use steel.
I did reasearch on this clutch here on py seamed to work great for other people. Me to good. I'm sure when the car is under load things will be fine. It sure move lots of air.

Originally Posted by Z Code 400

Steve,

The spacer is not reliable with a clutch. Use a longer clutch, like the one used on the V6 Buicks...Robert

[Z Code 400]

I would use steel.....and I would employ an 'hourglass' profile for light weight....similar to the oval track spacers currently available. With a 'flange' on either side of the hourglass, you could use studs in the water pump and studs in the spacer.

Providing you get the centering correct, this should be very durable...Robert

[70 Lemans]

Getting everything on center is a piece of cake. 5/8 Id 5/8 od. 5/8 ream for Id.

What is the most efficient distants from the radiator?

Originally Posted by Z Code 400

I would use steel.....and I would employ an 'hourglass' profile for light weight....similar to the oval track spacers currently available. With a 'flange' on either side of the hourglass, you could use studs in the water pump and studs in the spacer.

Providing you get the centering correct, this should be very durable...Robert

[Z Code 400]

1.5 to 2.5 inches blade to core distance...Robert

[lust4speed]

I would think that the fan is pulling the air through the radiator, and the air would be the same temperature 1" away or 3" away as long as a shroud is employed. I agree that without a shroud, the closer the fan is to the radiator the more efficient the draw through.