SteveG75

There is something wrong with your Vette. I have cruised all day cross country in July (100+ in Mid West) at 70 mph and my fans don't even come on. I have a 180 thermostat and the temp just sits there until I slow down.

If you don't have enough airfow, then you are probably missing the sealing foam between your radiator and the core support or the spoiler underneath. Both are essential to proper cooling.

DJ Dep

Let me add "there's something wrong with your Vette" too
They used this same fan clutch system on Vettes with engines that get VERY hot...never a problem. No service bulletins issued about problems with the fan clutch not providing sufficient power. Maybe you had a bad clutch. They DO wear out and when they go bad they won't provide sufficient cooling.

Dep

PhotoVette1

I just came back from a drive. It's about 90F sunny and I had the a/c on. The 'Vette runs right at 180F. If I drive at 65mph it runs right at 180F. If I go 70mph is when the temp climbs to 210F. I have a 180F t-stat and all the seals are new and in place--a new front spoiler too. Timing is 12d. With my rear end, I'm doing 3000rpm at 70mph.

One thing I don't hear is the fan roaring after I have stopped at a light--it should in this heat, at least for a few seconds.

Okay, time for a new fan clutch! Even though it is new--I'm betting it's defective.

DJ Dep

Easy ways to check the fan clutch.... Open the hood with the engine at idle and turn off the motor while watching the fan. If it continues to spin a LOT after you shut it off, it's probably shot. Second way...grab a fan blade with the engine off and see if you can "wiggle" the fan. If you can, fan clutch is shot. Third way, with the engine warmed up, hang on to the fan blade and have someone start the car. If you don't feel the blade pulling against you and trying to spin, then the fan clutch is probably shot. Be careful doing that third way. Fingers generally are NOT replaceable

Dep

Clint's C3

I guess I've never seen a declutching fan. All I've seen is a fan clutch that transmits a load from the fan pulley to the fan blades and does allow some slip. Are you saying the fan does not turn faster at higher RPMS? If you really want to dispute, we could confirm with a strobe light.

I'm still convinced the mechanical fan uses more power at higher RPMs.

Power = work / time. Work = force X distance. The drag (force)increases as wind resistance increases exponentially w/ respect to air velocity, thanks Bernoulli, Drag = 1/2 (coeficient of Drag) X ( density of air ) X Velocity squared. Distance the load moves also increases with RPM. So, not only are you moving against a larger load, you are moving the load futher (work = force X distance). Not to mention you have to accellerate the mass of the fan.

DJ Dep

Clint: The fan freewheels at highway speed. There are two types of fan clutches. One has a metallic heat sensing strip and when the engine gets hot the metal strip senses the heat drawn over it and freewheels the clutch. There is silicone inside the clutch to provide this freewheeling effect. That's why you should ALWAYS store a fan clutch "upright". The silicone CAN leak out of it if stored flat.
The other type works on centrifugal force and just freewheeels at speed/high RPM no matter what the engine temp. The factory puts the heat-sensing type on. You can get replacements in either type. The fan is spinning at high RPM, but nowhere near as fast as the engine is spinning.

A mechanical fan WITHOUT the fan clutch DOES use more power than a declutching fan. That's why all the performance engines as well as engines with A/C are equipped with fan clutches. Less drag on the engine and better cooling.

Dep

ACECO

Well as much as I hate to admit it, I'll have to go w/Dep on this one.

The whole idea of the fan clutch is to allow the fan itself to "declutch" at higher speeds and freewheel. In other words the water pump shaft will spin a lot faster than the fan itself. I'll grant you there probably is some minute load increase as RPM's increase, but certainly not nearly as much a standard mechanical fan w/o the fan clutch.

FWIW.

Clint's C3

I'll have to agree also, to a point. A "declutching" fan sounds like the one to have. I've only seen the OEM type as Dep well described, “with a metallic heat sensing strip and when the engine gets hot the metal strip senses the heat drawn over it and freewheels the clutch. There is silicone inside the clutch to provide this freewheeling effect". This fan has no extra freeweeling effect at high RPMs and load is determined by temperature.

So, unless you have a declutching fan, the speed of the fan and the drag, load, would increase with RPM rise. Of course, the Flex Fan guys would say that the Flex Fan flattens at speed to reduce drag, but that's a whole other discussion.

WayneLBurnham

A)"All the performance engines use fan clutches." Sorry, no way. Maybe in OEM/vette land, but not in the larger performance community. Until the electric fans got better and better flow, you would have a hard time finding a non-factory performance car of any type with the fan clutch instead of a flex fan. It's not that clutches can't work, it's that they are a part that ages and can fail. Now few use mechanical fans at all.

B)"Electric fan equipped vehicles run super hot under the hood." ALso not correct. Those vehicles MAY runn hotter than older vehicles, but it is not because of the fans. *Modern* electric fans way, way out perform mechanical fans in airflow through the radiator, either standard low rpm aggressive blades on factory fans to be used with clutches or clutchess flex fans where the fan blades flatten out at higher rpm. This was not true by the mid '80's but it is now. An electric fan mounts right against the radiator, not half a foot from it and does not rely on second level flow/suction containment schemes to pull efficiently. Take a look t the gap, especially on the sides to allow for engine movement, on your mechanical fan. This can easily exceed an inch even with a perfect condition shroud.

C)"Slanted radiator performs poorly" Incorrect. These cars come with decent sized radiators and the verticality does not matter at all except for the problem with air pockets forming easier and being tougher to get rid of. The problem, as others have noted, is poor air flow from the nose with or without fan considerations. Even with the lowest possible air dams the air flow off the front of the car is much less than that of a higher profile vehicle with a flat face going straight to the radiator. In the summer, where road surface temperatures can reach 150-160 degrees, another overlooked problem is the air actually being gathered by the front air effects is much hotter than that of a vehicle further off the ground - or, rather, where the average "height" of an air "particle" hitting the radiator is several feet higher.

D)"More power consumption at higher rpm - why not?" With a clutched fan, the fan blades do not flatter out much at higher and higher rpm, but the clutch is designed, in addition to "locking up" past a certain temperature, to not allow a maximum rpm beyond a certain point, where they begin slipping again, exactly as if it was cooler and not engaged. With a flex fan, they are called "flex" fans because the blades are designed to flatten out past a certain rpm, less as a concern of more and more parasitic loss at higher and higher rpm (although that is a design feature also) - or because in more traditional profiled vehicles you don't need air flow help at higher speeds - but primarily to allow such a fan to survive at up to 10,000 rpm. Again, aside from the slowest rpm motors, you should never, ever, ever run a non-flex fan without a clutch - they won't flatten out the blades and hence won't take the rpm. (I suppose you COULD run a clutch with a flex fan, although I can't see why - the larger numbered factory fans flow decently.)

E)Flex fan durability. Photovette was it? Guy - flex fans are built STRONGER than factory specs. That could have happened with any fan, and has happened with factory fans. Hayden is a good company too. That is, however, one other good thing about fan clutches - they are less likely to push a fan of any kind closer to failure.

F)"Grab ahold of a clutched fan when running the engine." Wow. Anyone who would do that has both a lot more guts and a lot few fingers, arms, face, head, blood, etc. than I ever will. If you really feel you have to run such a catastrophic test, they make these things called 2x4's? Jam one of those in there and the worse that happens is you damage a radiator or some minor accessories. True, by design a clutch should only fail by freewheeling, but don't test out all possible error conditions with a big sack of corrosive blood which will ruin the steel parts on your vette for the next owner.....

G)Yeah guy, you do still have a problem. Then again, so do I. With high end electric fans, like Zirgo or Spal, you can eliminate most of the concerns from air flow, regardless of air dam or radiator shorud seals or hood to support seals or anything. That might be it, that might not.
My problems seem to be controllable just with this five row copper, a constructed super shroud and spending a lot of effort plugging all the air flow leaks and forcing the front scoop down with two pieces of all thread rod, enough for me to have gained ground with the 460hp/500ftlb motor now in where the 225/300 ran a year ago - but not enough. I now seem to run 100-120 above ambient.

I went ahead and got a Dewitt's (came in two days ago), a 4kcfm Zirgo 16", a 1500cfm Zirgo 9" and a 1000 cfm Zirgo 8" (latter two are here) because I'm more concerned about the real engine to come and I want to be able to cross deserts in summer while hitting it hard.

My motto is "there's no kill like overkill!"

DJ Dep

Wayne: Three reasons why performance cars would have a flex fan in the old days rather than a declutching fan.

#1 The car is used ONLY for 1/4 mile dragstrip duty and the rules required it. They usually would install a small diameter flex fan blade to reduce weight and parasitic drag. But they only raced and ran the engine for a very short time.

#2 Those same guys got contingency money for using the flex fan.

#3 People didn't REALLY know the benefits of the declutching fan vs the flex fan. I know MANY people who took the fan clutch stuff off and installed a flex fan because they thought it would cool more efficiently or because their favorite racer was doing it that way. Amazing what advertising hype does to people .
EVERY performance car I bought was factory-equipped with a declutching fan. Interesting that they are STILL installing fan clutches on vehicles to this day. For a while Ford switched over to flex fans in the early 70's, but ended up going back to fan clutches. Probably because of the "noise factor".

On testing the fan clutch:
If you look closely, you'll see I said "Third way, with the engine warmed up, hang on to the fan blade and have someone start the car." I did NOT say "grab the fan while the engine is running". But an interesting side note....at the Lars tuning session in Chicago last weekend Lars told us that he knew a guy that did use that method of grabbing the fan blades while the engine was running to demonstrate the clutch effect. You just have to make sure the engine is completely warmed up

Dep

PhotoVette1

I imagine if you had a new flex-fan self-destruct at highway speeds and tear the crap out of your engine compartment, you probably wouldn't use one either. And ,as I said, Hayden treated me very very well. However, one of the things they did for me was give me a new HD fan clutch. Here is the results of my testing:

Back to my overheating on the highway problem. Here's the result of my fan/clutch testing.

In the garage: After turning on the a/c and blocking the radiator some, I ran the engine up to 2000 rpm.

The fan clutch would engage (air roaring out) then disengage (mostly) after 15 seconds or so--when the air temp got cooler--normal.

Then I ran it up 2500rpm--same thing happened--clutch disengages, but not all the way.

Then I ran it up to 3000rpm--what I cruise at on the highway. This time the clutch totally disengaged! About as much air flow as at idle.

Remember, at 65mph she runs cool, at 70mph she runs hot--2700rpm vs. 3000 rpm. The temperature doesn't jump to 210F, it slowly creeps up after about 15-20 minutes.

Am I looking at my problem?

And, what's the difference between HD clutchs and standard? I was told that a HD clutch gives you 80% of engine rpm and Standard gives you 50% of rpm--both when fully engaged. Is that right?

Mike Ward

Do you have a chin spoiler in place? My car would do the same thing without it.

WayneLBurnham

Mine still does that a little too, although it's past about 3500-3700 - really passed 4300 now. That rpm is where the flex fan flattens out or clutches start freewheeling and supposedly the directed air flow from the front of the car is expected to take over and exceed any fan-induced air flow. If there is a channelling air deficiency, that's where it shows up.

Dep - we ALL nuked the clutches - but again it was over failed older clutches more than anything else, and more on regular junkers than just actually raced vehicles.... On a $1,000 might make it go to work special, $50 for a flex fan and $30 for a spacer was NOT a desirable thing, just inevitable when the clutch went out and lef tyou on the side of the road in July. Overall I like clutches, except, I don't like manual fans at all. (Mine currently has a flex fan, but, then again, it came with it.... )

No, I realize you didn't say that - I was paraphrasing/generalizing. Guy, I WATCHED my idiot friend DO that "to impress a chick"!!! BTW, he got a decent cut on a few fingers. I don't remember if the chick was impressed or not (or whether she was WORTH impressing now!) but I do remember being furious at MY car being used as a test bed for advanced stupidity!

DJ Dep

Wayne: LOL...I think I'd be pissed too!!!

Note that both the L-88 and the ZL-1 both came equipped with fan clutch systems from the factory. That tells me they gotta be pretty good and worth having. Plus I think they look



Dep

rogie

My '80 vette with the 425 hp 383 stroker would run really warm even with a new 4 core rad and the stock fan with clutch. I put on a 6 blade plastic fan and got rid of the clutch. What a big difference...I'd never go back to the clutch fan again....temps at any speed are around 175 to 180 degrees...even running in parades at idle speeds and plus 85* the engine still runs under 190*. The 6 blade plastic fan is the best, cheapest & easiest investment to solve your cooling problems.
Another test for you is to take and put some insulated starter wrap around your temp sending unit...I'll bet your temps drop...mine did...the heat from the exhaust seems to register in your sender.

djcwardog

I ran into difficulty figuring out which NAPA fan clutch to use on my '73 big block with factory a/c. Yes, they sell a regular-duty one and a heavy-duty one. In my case I was replacing the flex-fan that came on my car with a new fan (from a vendor here). I wanted to save about half the price of that vendor's fan clutch so I went NAPA. Turns out that I needed the heavy-duty NAPA fan clutch to mate up with the fan I got. Yes again - for attaching the fan to the fan clutch the bolt patterns are different! Take your stock fan with you to match it up to whatever fan clutch they give you.

Clint's C3

I just hate to lose an argument. On the elec vs. mechanical fan question. I believe the elec is more efficient. Lots of arguments to the contrary. Following is a post regarding the easiest way to add 10 HP, from a Sr. member with a Vette that turns 11s. He obviously knows of what he speaks.



--------------------------------------------------------------------------------

$100 Permacool 2950 cfm electric fan and eliminate the mechanical fan.. That's about a 10 HP gain at the rear wheels...

GrandSportC3
CF Senior Member

Cruise-In IV Veteran
Cruise-In V Veteran
St. Jude Contributor

Member Since: Jul 2001

DJ Dep

Clint!! HA!!!! You just shot yourself in the foot quoting that guy!!!
He can't even figure out what kind of transmission to use, or if he is driving a race-only car or a street/strip car.
All that post prooves is the electric is AS GOOD AS the mechanical fan at cooling the engine.

Dep

Mike Ward

Not in this case. The test in question was on a dyno where the engine was hot enough to cause the fan clutch to lock up while at idle. The dyno crew then did a 'pull' in this condition and noted that the peak output was about 10 HP less than a previous pull when the fan clutch was NOT locked up.

The conclusion that a clutch fan eats 10 HP is therefore misleading for two reasons.

1) a clutch fan FREES UP 10 HP compared to a standard fan when the clutch is in freewheeling (normal) condition

2) The 10 HP "loss" was at or near engine red line. Who (in the real world) revs their engine to redline when it's hot enough to cause the fan clutch to kick in?

If the car in question had an electric fan similar in air-moving properties to the stock fan and the same test was done, I'm sure the losses would be similar or possibly greater.

It is an abberation of the laws of physics to believe that it is 'more efficient' to turn mechanical motion of an engine into electricity by driving an alternator, then turn the electrical energy back into mechanical motion through an electric fan. Far more efficient to just drive the fan mechanically in the first place.

WayneLBurnham

the power is taken. With an electric fan, the power does not come, immediately, off of the flywheel. Thus more engine torque is conserved. Greater energy is ultimately lost through the conversion from mechanical to electrical and back again, but this is through the electrical "spring" of the battery. An electric fan will not increase fuel economy, but will give more power to the wheels at demand. I don't have a good feeling for weight differences between a clutchless flex fan and an electric fan with it's motor but lighter blades. Fan clutches certainly are not light. Either way, it's minimal on the weight front.

My chief advocacy of them however is they cool better. They mount almost directly to the radiator, obviating the need for perfect sealing of shrouds, fairings, routing of incoming air, etc. (The need for channelling incoming air for traditional fan setups is, by itself, a way to lose power aerodynamically, BTW.)

A point missed is electric fans are also typically thermostatically controlled, just as via a fan clutch on mechanical fans.

No one has yet answered my question on whether an alternator actually causes more drag when it is sending current to the battery versus when the circuitry decides this is not needed (i.e. Is an alternator actually ever at idle? Does it always pull the same load, mechanically, and does it just sometimes actually use the power generated or does it "turn on" via establishing a field through the brushes and thus cause an increase in braking force?) I honestly do not know either way - I buy them based on amperage, one wire"ness", pretty/shiny/gaudy chromey"ness" and so on.... "Oh baby, I only DRIVES 'em - I don't know what makes 'em WORK!"

If an alternator really is always causing the same drag, whether charging is going on or not, then anything that uses the excess electricity not being used to charge the battery under minimal drain conditions is an improvement in efficiency - up until the point where a higher amperage alternator is required at least.

Electric fans, like electric fuel pumps and electric water pumps (which are not yet in general use) do reduce immediate power losses off the flywheel. Additionally, they reduce water pump wear and running imbalances on the reciprocating assembly. Even better, they can run after the engine is shutoff - a major improvement to combat near failure conditions on short term shutdowns (electric water pumps are REALLY great on this front...)