[Motor Daddy]

Originally Posted by Joel Koontz

Thermal fans only***FULLY***engage when the bi-metallic coil gets hot enough to engage the fan clutch.

I have never seen a thermal fan setting still when a motor is running so there is SOME drag being created by the fan. How much I don't know, perhaps 5 or 10 percent, but it is taking place the entire time the engine is running.

Even if the fan was not rotating in relation to the engine while the engine was running, it would be robbing the engine of power, because the friction of the oil would be a load (torque) on the crank. The torque*RPM/5252=HP.

[dmac]

You can prevent any excess alternator drag at the track by simply turning off the fan, especially with an electric water pump. But you probably don'y want to "turn off" your mechanical fan by removing the belt. If you are using electric fans for hp reasons, you may as wel use an electric pump too.

[dmac]

Originally Posted by lust4speed

Thermal fans only engage when the bi-metallic coil gets hot enough to engage the fan clutch, otherwise you only have the parasitic draw of the fan belt. Electric fans are only 80% efficient at best, and running the alternator to power the electric fan wastes that 20%. So an electric fan is less efficient on a daily driver. Electric fans are such a draw that I do shut off my electric fan on the drag car when pulling up to stage -- might not make that big of difference, but I feel better. When I pull to the return road I switch the fan back on and the alternator loads down -- all I did was trade a little less drag for a few seconds (OK, many seconds in my case) to be paid back on the return road. On the street providing the same cooling, the electric fan has to pull more energy due to its inherent inefficiency. That 45 amp load of the Mark VIII on high speed is quite a load.

I think this is wrong. An electric motor is much more efficient that a gas motor, so using gas to drive a fan has to be less efficient. Now the fact that you are using gas to run the alt to run the fan is maybe less efficient, but electrically controlling the fan by engine temp is more efficient than the bi-metal strip controlling the clutch that is affected simply by the air rushing over it than by actual engine temp so a mechanical has to be set to come on early.
Another point in favor of electric is that they should be able to be placed in a more efficient position, right on top of the radiator. Unless you have perfect shrouding, a closer fan will move more air through the radiator. Then you have the effectiveness of a pusher fan taking advantage of the direction the air is going in without an obstruction (the radiator) slowing the air down before it hits the fan. Imagine sitting on the engine side of the radiator. Is it easier to suck air thrugh the radiator, or to sit on the other side and blow through it? Even if you are back an inch, you get more air through the radiator, not from around it, by blowing through it, from as close as possible. You can't do this with a mechanical fan. If mechanical fans were as good, they would still be using them.
Overall, a thermostatically controlled electric well placed is going to be better than any mechanical, plus it can be shut off for the few seconds of racing.

[Motor Daddy]

Originally Posted by dmac

I think this is wrong. An electric motor is much more efficient that a gas motor, so using gas to drive a fan has to be less efficient. Now the fact that you are using gas to run the alt to run the fan is maybe less efficient, but electrically controlling the fan by engine temp is more efficient than the bi-metal strip controlling the clutch that is affected simply by the air rushing over it than by actual engine temp so a mechanical has to be set to come on early.
Another point in favor of electric is that they should be able to be placed in a more efficient position, right on top of the radiator. Unless you have perfect shrouding, a closer fan will move more air through the radiator. Then you have the effectiveness of a pusher fan taking advantage of the direction the air is going in without an obstruction (the radiator) slowing the air down before it hits the fan. Imagine sitting on the engine side of the radiator. Is it easier to suck air thrugh the radiator, or to sit on the other side and blow through it? Even if you are back an inch, you get more air through the radiator, not from around it, by blowing through it, from as close as possible. You can't do this with a mechanical fan. If mechanical fans were as good, they would still be using them.
Overall, a thermostatically controlled electric well placed is going to be better than any mechanical, plus it can be shut off for the few seconds of racing.

Bulls-eye.

[Half-Inch Stud]

Boy, tell you what; the mid-90's Lincoln MECH fan is probably the peak of optimal design.
While the Electric fan in fornt of it fails the 30 Amp Fuse on nearly every Lincoln. Been street-driving & towing with only the Mech fan in tha tLincoln and that Temp gauge stay put on "Normal" in all weather & driving situations.

Soooooo, I tried to get me a spare Lincoln fan for the U-Pull-it (for the 68GTO) and geez it is a "Ford" design to the point of high-difficulty to transfer to the Pontiac. Could be done but at high effort.

Makes me re-consider the elec fan.

Butt, that Lincoln Mech fan really decouples well (the best de-clutching "neutral" I've ever seen) when not needed.
================================================
During the re-camm effort going on, I gots a Mech Fan decision to make.

[David Holmberg]

Electric fans are worth a little in the performance and mileage areas according to new car mfgs.

However *** in a HD cooling application mechanical fans are used. Every 3/4 - 1 ton Diesel truck that I've seen comes with a mechanical fan.

When towing with my 460 HP, 875 TQ Diesel, I can tell the difference when the fan comes on.

With my BBC Suburban, when the fan comes on while towing I lose speed. It does make a difference. Both are when towing around 10K lbs.

[Steve C.]

Based on what I've read in performance articles they suggest it is better to have the elec fan mounted to pull air thru a radiater rather than push it thru.

[Motor Daddy]

Originally Posted by David Holmberg

Electric fans are worth a little in the performance and mileage areas according to new car mfgs.

However *** in a HD cooling application mechanical fans are used. Every 3/4 - 1 ton Diesel truck that I've seen comes with a mechanical fan.

When towing with my 460 HP, 875 TQ Diesel, I can tell the difference when the fan comes on.

With my BBC Suburban, when the fan comes on while towing I lose speed. It does make a difference. Both are when towing around 10K lbs.

Most big engines like CAT, Cummins, and Detroit use air pressure to lock and unlock the mechanical fan clutch. I used to start the Diesels in the morning with the hood open and watch the fan stay perfectly still, while the engine was running. When the fan clutch actuator opens when coolant temps get high enough the actuator opens and air pressure locks the clutch. That's when you hear some fan noise, and lots of it.

HMMWV's (Military Hummers) use power steering fluid pressure to unlock the fan clutch.

[1971WARBIRD]

Originally Posted by motor-daddy

HMMWV's (Military Hummers) use power steering fluid pressure to unlock the fan clutch.

we used hummers to escort convoys in Iraq,running up and down the length to keep them in line.when that fan kicked in at 60/65 mph it was like throwing out an anchor.

[Motor Daddy]

Originally Posted by 1971WARBIRD

we used hummers to escort convoys in Iraq,running up and down the length to keep them in line.when that fan kicked in at 60/65 mph it was like throwing out an anchor.

Yup, when the fan is locked you can feel the truck instantly start to feel like a dog. I'd be on the autobahn in my Hummer running hard to hurry up and fix somebody's broke sh!t and when the fan kicked in it used to piss me off. I'd be cussin' at the damn thing for slowing me down.

[1971WARBIRD]

Originally Posted by motor-daddy

Yup, when the fan is locked you can feel the truck instantly start to feel like a dog. I'd be on the autobahn in my Hummer running hard to hurry up and fix somebody's broke sh!t and when the fan kicked in it used to piss me off. I'd be cussin' at the damn thing for slowing me down.

noisy as h*ll also

[Motor Daddy]

Originally Posted by 1971WARBIRD

noisy as h*ll also

The M939 series 5 ton vehicles fan would scare the crap out of you when it kicked in at 50 MPH. When that thing locked it made a hell of a racket. No power when locked. None.

HMMWV's have a mechanical governor in the injector pump that kicks in roughly when the speedometer is an inch past buried (60 MPH Speedometer IIRC). When the fan clutch is locked the engine will not run up to the governor. In the other case it was the injector pump I was cussin' at.

[Kenth]

Originally Posted by dmac

I think this is wrong. An electric motor is much more efficient that a gas motor, so using gas to drive a fan has to be less efficient. Now the fact that you are using gas to run the alt to run the fan is maybe less efficient, but electrically controlling the fan by engine temp is more efficient than the bi-metal strip controlling the clutch that is affected simply by the air rushing over it than by actual engine temp so a mechanical has to be set to come on early.
Another point in favor of electric is that they should be able to be placed in a more efficient position, right on top of the radiator. Unless you have perfect shrouding, a closer fan will move more air through the radiator. Then you have the effectiveness of a pusher fan taking advantage of the direction the air is going in without an obstruction (the radiator) slowing the air down before it hits the fan. Imagine sitting on the engine side of the radiator. Is it easier to suck air thrugh the radiator, or to sit on the other side and blow through it? Even if you are back an inch, you get more air through the radiator, not from around it, by blowing through it, from as close as possible. You can't do this with a mechanical fan. If mechanical fans were as good, they would still be using them.
Overall, a thermostatically controlled electric well placed is going to be better than any mechanical, plus it can be shut off for the few seconds of racing.

Sure they would, if they only found a way to mount them on a sideway mounted engine?

[KS circutguy]

Bingo

[KS circutguy]

Best setup imo for street strip car is oem thermal fan clutch setup.

[Motor Daddy]

Originally Posted by KS circutguy

Best setup imo for street strip car is oem thermal fan clutch setup.

Define "best."

[Joel Koontz]

New Corvettes and late model Trans Ams don't have their motors mounted sideways and they do not use mechanical fans

[Half-Inch Stud]

Yea, that mid-90's Lincoln Mechanical cooling fan has to be to optimal design. Yeap.
Got 2 Lincolns and BOTH Elec fans are disabled. Yea, never notice that fan doing it's job, highways, towing, sideways, all quiet.

[Motor Daddy]

If you use a mechanical fan it requires the rotary motion of the crankshaft to be engaged and disengaged at a proportional ratio to the gear ratio of the pulley belt system. At some point there is work being done, whether it be friction in a bearing, or heat that is lost, etc etc. That means the system is robbing power from the engine. Power=work/time.

In an electrical circuit, when the circuit is open there is absolutely ZERO work being done.

The electrical fan only works when it has to, only as much as is needed, and is way more efficient when it is doing work.

Engine coolant temperatures often get hotter when the engine is run to normal operating temps and then shut down. Electric fans can and will run even when the engine is not running.

Less pulley and belt system required=less maintenance. Electrical systems are generally more maintenance free than bulky heavy mechanical systems.

[David Holmberg]

MD, you need to add that when an electric fan is running the load on the alternator is higher, causing an extra load on the motor.

Otherwise, I agree.