Flex Fan Diameter and spacer size?

[Derrick]

Quick question for you guys. What diameter flex fan do I need for a 75 L48 and what thickness of spacer?

I'm going to go with the Flex-a-lite brand 6 blade setup.

Thanks in advance!

 

[Vettehead Mikey]

If it's not too late, please don't downgrade your car with a 'flex fan'. The stock fan with fan clutch ass'y is a far superior piece in terms of efficiency and reliability.

 

[tat2ed]

Doesn't the flex fan provide better air flow since it is a one piece system? I thought there would be slippage with a clutch type fan. What makes the clutch fan better?

 

[Vettehead Mikey]

It may provide more flow at high engine speed depending on the design, but that's not a required or desirable feature. Max flow is required at LOW engine speed to handle bumper to bumper traffic situations. The stock fan and fan clutch does a perfect job of that.

High engine speed is usually accompanied by high vehicle speed. The ram flow through the radiator provided by the forward movement of the vehicle is sufficient, no fan needed.

That's the beauty of the fan clutch, locks up when the engine is hot and releases when it's not.

The big drawback of the flex fan is they drive air (and noise) 100% of the time. There are also many reports of flex fans loosing blades or coming off the engine completely, doesn't sound like something I need under the hood.

 

[Evolution1980]

It may provide more flow at high engine speed depending on the design, but that's not...a desirable feature.

Why is more air at high engine speed not desirable?

The big drawback of the flex fan is they drive air...100% of the time.

Why is driving air 100% of the time a big drawback?

There are also many reports of flex fans loosing blades or coming off the engine completely, doesn't sound like something I need under the hood.

There are also many reports of clutch fans going bad and people's cars overheating. Doesn't sound like something I need under the hood.

We each probably know more people with clutch fans or flexfans that haven't failed than those that have failed.

...just playing devil's advocate.

Derrick, if I happen to remember to do so tonight, I'll see what I find out about my setup. It's been years since I first installed mine and I don't remember the specifics.

 

[JohnZ]

A flex fan is a lousy substitute for the correct factory fan and clutch, for the reasons Mikey noted; if they were so good, GM would have used them. At highway speed, flex fans actually reduce airflow through the radiator; thermo-modulated clutch fans decouple at normal coolant temperatures and over 3500 rpm, and flex fans don't. The engineers spent thousands of hours and millions of dollars developing cooling system components that work under the full range of operating conditions; you can't out-engineer them piece-by-piece out of a hot-rod catalog - that's why it's called a cooling "system". :eyerole

 

[Evolution1980]

A flex fan is a lousy substitute for the correct factory fan and clutch, for the reasons Mikey noted; if they were so good, GM would have used them. The engineers spent thousands of hours and millions of dollars developing cooling system components that work under the full range of operating conditions; you can't out-engineer them piece-by-piece out of a hot-rod catalog

Then why aren't they still using 'em? :confused :eyerole
For the same reasons any individual component or entire systems aren't used anymore. Advances and better technologies. Why aren't we using the same suspension geometry from 1973 on the C6's? Because they have better designs now. Maybe they didn't use flexfans back then because they didn't have 'em or they weren't as structurally solid as they are now. I don't know...

I'm not saying that flexfans are any better or worse than the OEM setup, but you and Mikey are making Flexfans out to be the devil and now you blanketed any other potential "upgrade" or replacement part from a 'hot-rod catalog'.

He will probably notice zero difference between a flex fan and a clutch fan. If his clutch fan is broken, then it's likely cheaper to get a flexfan. And he may like the looks of the flexfan better. I know I do. I've had mine for years and have had zero cooling problems with my car at any speed for any duration.

I'm happy that we can offer him suggestions/advice, but at least answer his question as well. As of yet, no one has given him the answer he's looking for.

(Not trying to be snippy or overly sensitive. I'm a little irritated at other things not related to you guys or anything having to do with the CAC and it appears to be manifesting itself in my post. )

 

[Vettehead Mikey]

Why is more air at high engine speed not desirable?

Why is driving air 100% of the time a big drawback?

It costs engine HP to drive a fan, no matter how little that may be. If the ram air by itself is 'getting the job done,' spinning the fan any faster than necessary is pure waste. Noise is also a factor.

 

[Vettehead Mikey]

Then why aren't they still using 'em? :confused :eyerole

They're still used on plenty of vehicles- my last Infiniti had one. Sometimes radiator position and location with respect to the engine accessory drives makes it impossible to use a mechanically driven fan of any type. My present daily driver has too low a nose to fit one so it has an electrically driven one instead.

I don't know of any vehicle that came from the factory with a flex fan.

With respect to reliability, clutch fans usually die a prolonged death giving the owner plenty of warning of impending failure. From the little I know of flex fans, a blade release happens with no warning at all.

Flex fans have been around since at least the '70s. I can remember them in all sorts of day-glo anodized colours. Looked faaaaaar out back in the disco daze!

 

[petes74ttop]

Hi Derrick, well you sure got some answers there, it's your car and if you want a flex fan than go for it. I agree with JohnZ and I will not re-engineer my car, for the most part I figure that GM spent time and money so that my car would not over heat and most of the parts that I replace are stock, at least in the cooling system. Also you should use a 180* robert shaw thermostat. PG

 

[Crimson Thunder]

Make sure you use high quality bolts to mount the flex fan and its spacers.If one of those long 4inch bolts fail at 5000 RPM it will be a bad day for your radiator and possibly your hood.

 

[tat2ed]

what is the indication that the clutch is going out in the fan? Does it stop spinning or just freewheel? Or does it not disengage?

 

[petes74ttop]

Quick question for you guys. What diameter flex fan do I need for a 75 L48 and what thickness of spacer?

I'm going to go with the Flex-a-lite brand 6 blade setup.

Thanks in advance!

I think the stock fans were 17 1/2 in diameter, Not sure about the spacer, PG

 

[Evolution1980]

Derrick, if I happen to remember to do so tonight, I'll see what I find out about my setup. It's been years since I first installed mine and I don't remember the specifics.

I got 18.5" for the approximate diameter of the fan. Since I couldn't actually get an end-to-end measurement across the true center of the fan, I had to approximate.
The spacer is definitely 2" as shown.

I'm pretty sure that this fan may be the one you want...
This could be the spacer.

NOTE: My answers are not "for sure". They are "I'm pretty sure, but I could be wrong" answers.

 

[Derrick]

Thanks for the reply guys....sorry I've been MIA. Been traveling on business and haven't had a chance to respond.

Current condition of the car is that is cools absolutely fine in city traffic....temp is always less than 200....but the temp tends to clim to 220 - 240 at highway speeds. Car has a new water pump, correct fan shroud, and 180 thermostat...also new.

I figure the fan clutch is bad and I like the look of the flex fans. I think the flex fan technology is better than that of the 1970s technology. My occupation is engineering so anyway I can make the car more efficient with new technology the better....plus the flex fans are cheaper than a new clutch.

I've ordered a 17 1/2 flex fan with 2" spacer. After posting this question and seeing some of the comments I did a more in depth search on this forum and found the following thread to be very useful:
http://corvetteactioncenter.com/forums/showthread.php?t=3787&highlight=fan+spacer


I'll post an update once I get the flex fan on the car next week. Thanks for the input

 

[Vettehead Mikey]

Current condition of the car is that is cools absolutely fine in city traffic....temp is always less than 200....but the temp tends to clim to 220 - 240 at highway speeds.

Then your problem is NOT with the fan or fan clutch. You most likely have a problem with insufficent airflow through the radiator at highway speed.

Do you have the chin spiler in place and all the radiator shroud air seals? How old is the radiator?

 

[Derrick]

Then your problem is NOT with the fan or fan clutch. You most likely have a problem with insufficent airflow through the radiator at highway speed.

Installed the 17" flex-a-lite fan and 2" spacer yesterday with excellent results. The car's temp during normal city driving is 10-15 degrees lower than before. We also tested the highway performance with even better results! After several miles on the highway at 70mph the temp never reached 200 degrees. In fact I even picked up the speeds to 80 and 90 mph for a few minutes without the temp climbing past 195 degrees. Before installing the flex fan the engine temp would have climbed to 220-240 degrees easy.

I'd highly recommend the flex fan for any of you that are considering. At a total price of under $60 from summit which included the fan, spacer kit and handling charges, it's a definite bargain! Looks good too.

I heard many people complain about the flex fan sound...but mine is unnoticeable unless you floor it. In my opinion it has a nice tone to it.

Also just a side note. The new flex fan and spacer weighed in at 3.4lbs and the old fan and clutch weighed in at 9.6lbs.

Thanks for all the posts relating to this thread!

 

[Evolution1980]

I heard many people complain about the flex fan sound...but mine is unnoticeable unless you floor it. In my opinion it has a nice tone to it.

I don't even notice the sound on mine. Maybe it's drowned out by my exhaust note? The only time I notice the fan at all is if I'm standing at the front of the car with the engine running at the hood up, just as you'd likely hear the clutch fan if it was engaged. Glad everything worked out for you. Happy Motorin'!

 

[Vettehead Mikey]

I'm glad you found a work around to deal with the problem, but this just proves the point- you are not getting enough air flow through the radiator to cool the engine properly.

I would be curious as to why it was needed above and beyond the stock fan. :confused

 

[Vette79]

Then your problem is NOT with the fan or fan clutch. You most likely have a problem with insufficent airflow through the radiator at highway speed.

Do you have the chin spiler in place and all the radiator shroud air seals? How old is the radiator?

This is something I will be looking at later today. I have the same exact problem. My radiator is new. Maybe the shroud air seals are the problem. What is a chin spiler?