Electric Fans - Who Needs 'Em>

[Jughead]

I agree with you TT :thumbs: The Dual Spal electric fans with a BeCool/DeWitts radiator has been one of the top upgrades I have made on RamJet.

Unless you get a really well-engineered dual-fan setup with a full shroud that covers the entire face of the radiator core (with pressure-relief flaps for added ram airflow at highway speed), they're a poor substitute for the factory fan setup,

This is something I have believed for a long time. Electric fans aren't worth all the expense of the conversion. So why is everybody going with electric fans?

Kid, how did you interpret the above statement into ---"Electric fans aren't worth it"?

Bullshark

The fact that I've never seen an installation that meets the criteria of a "really well engineered dual-fan setup" leads me to the statement that "Electric fans aren't worth it".

Here is a pic your setup from DeWitts web site.

The shroud only covers about 80% of the radiator surface. That would make it "a poor substitute for the factory fan setup".

I'm enjoying all the discussion in this thread. More intelligent discussion here in one thread than in ALL the threads in a month elsewhere. :thumbs:

That's the setup I'm using and my BB runs cooler than my SB did with the belt driven fan.

 

[Bullshark]

Ok, lets take a closer look at the stock setup and ask some fundamental questions. What is the efficiency of the belt driven clutch fan? CFM (ft3/min) over the rpm, vehicle speed operating range. What are the air flow dynamics? I don't have the exact data, so speculation and experienced results is all we have. I'm betting that the primary volume of air flow is centered in front of the fan with a substantial decrease in flow as you get out to the radiator perimeter even with the stock shroud. I maintain the dual electronic fan setup pulls significantly more air across a larger area of the radiator than does the stock setup. So the ~20% you refer to is additional area used only when the vehicle speed and load is up and requires even more air flow. Remember, the purpose of our cooling system is to maintain the engine at its optimum operating temperature range across the ambient environmental extremes.... 195-200 degrees engine temp measured at the intake manifold for my RamJet 502.
I have owned 3 BB C2-3 Vettes with A/C over my life and have experienced overheating challenges in all of them. St. Louis can be pretty hot and humid in the summer:quote::sweat:

On RamJet, I control the dual fans with the Accel Gen VII ECU. Fan #1 is programed to turn on at 198 deg and off at 188, while Fan #2 is programed to turn on at 210 and off at 204. With this setup I typically only use one fan on warm days during idle or heavy loads. The only time Fan #2 comes on is on a 99-100+ degree day with A/C. I have since modified my setup to also turn on Fan #2 whenever A/C clutch is engaged to optimize cooling efficiency. I personally could never achieve this kind of control with the stock setup. Again, this is done for the primary purpose of keeping the engine operating efficiently at 195-200 degrees under all operating extremes. If you can do this reliably with a mechanical setup, then your configuration is more than adequate.

Still one of the best investments I have made. :drink:

BTW, PWM fan speed control is a waist of money IMHO. :stirpot:

Bullshark

 

[Twin_Turbo]

If you really want to do it properly you'll need something like this:

 

[Bullshark]

Marck, Sorry, I can't tell which end is up?? or who's on first? Need more description or pics. Also, where is the pressure-relief i.e. ("flaps") or spare area outside the shroud for added ram airflow at highway speed?

Bullshark

 

[Twin_Turbo]

the red is the front lower edge of the bumper, you're looking up to the rear of the rad.

Relief flaps? The normal flow will just exit through the fans.

 

[Bullshark]

I don't run AC on anythig

Spoken like a man from the Netherlands. :lol:

Bullshark

 

[Kid Vette]

Ok, lets take a closer look at the stock setup and ask some fundamental questions. What is the efficiency of the belt driven clutch fan? CFM (ft3/min) over the rpm, vehicle speed operating range. What are the air flow dynamics? I don't have the exact data, so speculation and experienced results is all we have. I'm betting that the primary volume of air flow is centered in front of the fan with a substantial decrease in flow as you get out to the radiator perimeter even with the stock shroud. I maintain the dual electronic fan setup pulls significantly more air across a larger area of the radiator than does the stock setup. So the ~20% you refer to is additional area used only when the vehicle speed and load is up and requires even more air flow.
Bullshark

Based on what?

 

[Bullshark]

The point is, you have less control over temperature with no thermal reserve.

Turtle, the thermal reserve you refer to is the second fan, the added ram airflow at higher speed, and the higher volume of coolant delivered to the engine at higher rpm. At least that is what I believe my RamJet experience is telling me.

Bullshark

 

[Bullshark]

Based on what?

As already stated.......speculation and the minimal data spal provides. I agree, my premise has no more validity than it's mechanical counterpart. I have no real test data. :nuts: Just observed results.

Bullshark

 

[Belgian1979vette]

Is it a fact that the stock clutch quits turning faster from about 3500 upwards?

I would think that the clutch would only loose a certain percentage of revolution of the fan.

 

[Twin_Turbo]

it controls the MINIMUM operating temp. .

therefore it controls temperature. You're playing with words. We all know the STEADY STATE max operating temp is controlled by the system design parameters and ambient temperature.

But, you are making my point for me.

Ok, I'm playing with words...whatever! You know what I mean, I know what you mean. Thermostat does not control how hot the operating temp is. It controls how fast the engine warms up and minimum operating temperatures, nothing else.

The point is, you have less control over temperature with no thermal reserve. You want fans pulling air past the radiator at all times to keep the coolant in the radiator as low as possible at all times so the engine thermostat will have more control over the maximum operating temperature.

Let me spell it out. I'll use an extreme example. If the electric fans kick off until the radiator coolant temp hits 185. Then the engine thermostat opens at 190 the delta T is only 5 degrees. You then immediately make a quick blast up a mountain road. What do you think the system temp is gonna do. Probably hit 230.

With the mechanical fan turning all the time the radiator coolant temp is lower say 140. The engine thermostat opens at 190 so the delta T is 50 degrees. Now you make the same quick blast up a mountain road. You have a lot of cooling capacity there due to the large mass of cool coolant in the radiator. The max temp probably will not exceed 190.

And at speed, who is going to argue that a negative pressure behind the radiator to increase the delta P resulting in more flow through the radiator is a bad thing.?

BTW, When i owned my Regal Grand National i bypassed the electric fan thermostat so it would run all the time when the key is on. Yea, the fan needed brushes much sooner than it would have but that's a small price to pay to keep engine temps from spiking.

You don't switch the fans off the coolant temp in the radiator, not if you do it properly. You put the switch in the head, which always runs a good amount of degrees hotter.

I don't agree that at speed the fans should not come on at all, if they do your radiator core is too small, the airflow is insufficient or there's some other issue (like late timing). See you are reasoning that the mech fan is needed at speed but it's not, in fact the fan partially freewheeling in there possible isn't doing much at all, the airflow from driving will easily be overcoming the pulling power of the fan. The fan only becomes efficient when the engine bay is hot enough for the thermo clutch to lock it and at low speed where it actually helps draw air through the radiator. For the rest of the time it's just wasting energy.

Because of this your reasoning that the clutch fan will maintain a lower radiator core temperature will not hold water IMO. The other factors greatly overpower the ability of the fan to pull air through at speed and as such at when comparing both at the same speed the core temperature would be about the same.

Why use a clutch fan? maybe because they're cheap? If you're so worried about keeping things cool, a dual setup with staggered temp switching will cure all that temp spiking you're worried about.

If your clutch fan is so awesome, why did you warp your heads from overheating multiple times now? You yourself said you probably didn't have much meat left in the deck surface from all the resurfacing? Doesn't sound like it's working very well. :noworry:

 

[turtlevette]

The point is, you have less control over temperature with no thermal reserve.

Turtle, the thermal reserve you refer to is the second fan, the added ram airflow at higher speed, and the higher volume of coolant delivered to the engine at higher rpm. At least that is what I believe my RamJet experience is telling me.

Bullshark

NO, Thermal reserve is when the coolant in the radiator is significantly less than that in the engine. You don't get much if any thermal reserve when fans go off completely off until some predetermined temperature.

Go ahead and run electric fans, just run them both all the time.

 

[turtlevette]

You don't switch the fans off the coolant temp in the radiator, not if you do it properly. You put the switch in the head, which always runs a good amount of degrees hotter.

I don't agree that at speed the fans should not come on at all, if they do your radiator core is too small, the airflow is insufficient or there's some other issue (like late timing). See you are reasoning that the mech fan is needed at speed but it's not, in fact the fan partially freewheeling in there possible isn't doing much at all, the airflow from driving will easily be overcoming the pulling power of the fan. The fan only becomes efficient when the engine bay is hot enough for the thermo clutch to lock it and at low speed where it actually helps draw air through the radiator. For the rest of the time it's just wasting energy.

Because of this your reasoning that the clutch fan will maintain a lower radiator core temperature will not hold water IMO. The other factors greatly overpower the ability of the fan to pull air through at speed and as such at when comparing both at the same speed the core temperature would be about the same.

Why use a clutch fan? maybe because they're cheap? If you're so worried about keeping things cool, a dual setup with staggered temp switching will cure all that temp spiking you're worried about.

If your clutch fan is so awesome, why did you warp your heads from overheating multiple times now? You yourself said you probably didn't have much meat left in the deck surface from all the resurfacing? Doesn't sound like it's working very well. :noworry:

1. Why ever switch off an electric fan? Why let the system heat up?

2. My experience with my car over 28 years has been that the C3 is NOT self cooling at highway speeds. That's only 400,000 miles of testing though, maybe i should drive anther few hundred thousand to make sure. That's as many miles only on my C3 than you will probably drive in total your whole life living in a small country.:1st: Some of the early C3s had an opening behind the license plate to allow a more direct path for airflow, but later ones had only a very small spoiler to force air up into the radiator. These spoilers are eventually broken from hitting parking bumps ect. and cooling efficiency decreases. Even in perfect condition a C3 is still not self cooling at speed.

A thermo fan clutch does NOT lock. The torque characteristic increases but it never locks, but neither does it freewheel. There is always some resistance and the fan is always working to some extent. I can hear mine going in and out on the highway as the radiator alternately cools and heats up.

3. I don't understand what you're trying to say. Because of this your reasoning that the clutch fan will maintain a lower radiator core temperature will not hold water IMO. The other factors greatly overpower the ability of the fan to pull air through at speed and as such at when comparing both at the same speed the core temperature would be about the same.

4. A second electric fan will not be able to come on and cool quickly enough to handle a huge delta Q from a WOT event.

5. Both times i warped the heads were from neglect. The rad had a pinhole and i neglected to check the coolant level. Level got too low and caused the heads to fry.

 

[Bullshark]

The point is, you have less control over temperature with no thermal reserve.

Turtle, the thermal reserve you refer to is the second fan, the added ram airflow at higher speed, and the higher volume of coolant delivered to the engine at higher rpm. At least that is what I believe my RamJet experience is telling me.

Bullshark

NO, Thermal reserve is when the coolant in the radiator is significantly less than that in the engine. You don't get much if any thermal reserve when fans go off completely off until some predetermined temperature.

Go ahead and run electric fans, just run them both all the time.

Damn turtle....you going to make me dust off my old thermodynamics book?..:surrender: I can't remember all those thermodynamics laws, but I'm pretty sure they describe the heat transfer dynamics here. The relatively slow thermal time constant of this system allows plenty of time for the second fan, the added ram airflow at higher speed, and the higher volume of coolant delivered to the engine at higher rpm, to respond. That's potential thermal energy transfer reserve in this EE's mind. Hope I don't have to call in the thermal guys. :sos:

Two against one, turtle, .... better give it up. :clobbered:

Bullshark

 

[big2bird]

This is a GREAT discussion. About the only thing I picked up and disagree with is Turtle saying fan imbalance will not speed up water pump wear. Sorry Jim, no way. Fan imbalance will trash a water pump and/or fan clutch mucho fastero.

 

[turtlevette]

The relatively slow thermal time constant of this system allows plenty of time for the second fan,

Two against one, turtle, .... better give it up. :clobbered:

Bullshark

slow thermal time constant.......YEAAA on the way to the show n' shine.

The problem is you guys NEVER beat on your cars so you never see temp spikes.

2 against one, but science is on my side. I don't know as much about cars as you guys but i'm a pretty damn good engineer.....if i do say so myself.

 

[Kid Vette]

This is a GREAT discussion. About the only thing I picked up and disagree with is Turtle saying fan imbalance will not speed up water pump wear. Sorry Jim, no way. Fan imbalance will trash a water pump and/or fan clutch mucho fastero.

I suppose fan imbalance has no effect on an electric fan?:huh2:

 

[Bullshark]

slow thermal time constant.......YEAAA on the way to the show n' shine.

The problem is you guys NEVER beat on your cars so you never see temp spikes.

You haven't seen Ramjet's smoke. It's 10 to 2, ditch to ditch all the way to the show. :waxer: :yahoo:

Ok, I grant you that a big factor in this time constant equation is the radiator. That big BeCool aluminum radiator has a much better thermal transfer efficiency than that old clogged up copper one you probably have. :skeptic:.... Not to mention all the other variables.
Next time your in StL. give me a call, we will go to a show. :devil: :goodevil:

Bullshark

 

[big2bird]

This is a GREAT discussion. About the only thing I picked up and disagree with is Turtle saying fan imbalance will not speed up water pump wear. Sorry Jim, no way. Fan imbalance will trash a water pump and/or fan clutch mucho fastero.

I suppose fan imbalance has no effect on an electric fan?:huh2:

"ANY imbalance on ANY shaft with bearings will trash ANY bearing.":smash: Better?
I still feel Gene hit the mark with the transverse engine engineering solution. It solved a problem, and using the same setup with other powerplants reduces inventory.
As for WHICH is better for our cars, I leave it to the egg heads.

 

[Kid Vette]

Is it a fact that the stock clutch quits turning faster from about 3500 upwards?

I would think that the clutch would only loose a certain percentage of revolution of the fan.

It was stated as fact in the same article in CE. It also seems only logical. At higher RPMs there will be more and more resistance to the fan spinning, thus the percentage of fan RPMs compared to engine RPMs will get lower and lower. This same fan/clutch setup was used on 302 ci Z28s back in the day and we all know how rev happy they were. Never heard of a fan exploding on them.