Off Subject: Engine Driven Fan VS Electric Fan...

[Dennis C.]

...Just trying to put things in perspective. Most things being kinda' equal, will a well designed 6 blade engine driven cooling fan provide - more, the same, or less cooling potential than a well designed puller electric fan of approx equal "size"...??? Any way to quantify or qualify the difference that the dame bramaged folks of the world can understand...??? TIA, Dennis

[Duke W.]

Re: Off Subject: Engine Driven Fan VS Electric Fan

Too many variables to make a meaningful comparison. In addition to OD, blade design and number of blades are part of the equation, plus an engine driven fan's flow varies with engine speed. As a general rule, engine driven fans are "too big" in order to provide sufficient air flow at idle. The Corvette gets around this with the thermo-clutch, which is a very good idea to keep the fan from eating up too much power and making too much noise at high revs.

Most aftermarket electric fan suppliers provide flow rates, but I've never seen any published flow rates for OE engine driven fans at various speeds, so there's no baseline for comparison.

Some aftermarket fan suppliers provide basic guidelines on how to size the fan based on engine size, vehicle weight, type of service - for example, if you tow, a bigger fan is probably adviseable.

Also be sure your alternator will deliver sufficient output at idle to maintain system voltage and that your wiring is sufficient size to handle the alternator's total output.

A two speed fan would be a good idea - a low speed triggered at say 200-205 and a high speed at 220 or so. Another approach is to have two fans - the first activating at 200-205 and the second at 220. This also provides redundancy, which is always a good design idea.

Also be aware that if the car has A/C the fan should also be activated by a high-side pressure switch to keep high side pressure in check and maintain adquate condensing capacity.

Duke

[Patrick H.]

Re: Off Subject: Engine Driven Fan VS Electric Fan

Dennis,

Cooling aside, the electric fan will use less power and create less noise. If you're thinking of using this on your project mobile, there's only one way I'd go. I'm sure that the OEMs haven't gone to electric fans just for these reasons, but I doubt that they'd use them if they were a lot less efficient, either.

I'd also be sure to use an aluminum radiator.

Patrick

[Joe L.]

Re: Off Subject: Engine Driven Fan VS Electric Fan

Dennis------

Look at it this way: every Corvette built since 1984 has used electric cooling fans exclusively. Since all 1984+ Corvettes have a conventional, longitudinal engine configuration, they could have used a conventional engine driven fan. But, they didn't. There may be a "clue" here.

[Duke W.]

Re: Off Subject: Engine Driven Fan VS Electric Fan

Believe it or not the switch to electric cooling fans on longitudinal powertrain configurations is motivated by fuel ecomony. Not having an engine driven fan can increase the EPA fuel economy by a few tenths, which in some cases is enough to round to the next higher whole MPG number and help the OEMs with CAFE. Electric fan(s) also increase SAE net power because a fan does not have to be included with the "as installed" engine configuration power tests.

My '88 Mercedes 190E 2.6 has an interesting fan configuration. Leave it to the Germans of that era to leave no stone unturned and over-engineer the cooling system to obsession.

It has an engine driven thermo-clutch fan similar to vintage Corvettes, except the fan itself is plastic. The clutch themostat keys of radiator air exit temperature as is the case with vintage Corvettes, and it tightens at about 100C coolant temperature. The thermostat opening temperature 87-90C.

Added to this are TWO, TWO-SPEED electric pusher fans in front of the radiator that are keyed off two systems. The low speed (both fans) is activated by a pressure switch on the high side of the A/C system, and high speed (both fans) is engaged by a 105C themoswitch in the cooling system. The two speeds are achieved by adding a resister to the circuit for low speed, which drops voltage at the motors. This is a ceramic cased resistor, which looks very similar to the ignition ballast resistor on vintage Corvettes.

The throttle linkage is even more amazing, but that's another story...

Electric fans are more "efficient" because they are only energized when necessary, which is usually at idle or low speed stop and go driving. At any speed above about 25-30 MPH dynamic pressure is sufficient to provide adequate cooling for most cars, so an engine driven fan, even a thermo clutch of flex blade type, just becomes parasitic loss, which increases fuel consumption for no benefit.

Duke

[John H.]

Re: Off Subject: Engine Driven Fan VS Electric Fan

The configuration of electric fans also varies widely. The typical catalog fan housing is round and attaches directly to the radiator core, which means air is only pulled through the circle described by the fan, so only about half of the radiator core is doing any cooling. The factory engine-driven fan uses a shroud that pulls air through every square inch of the core surface, all the way out to the corners, utilizing the entire core for cooling. Sealing the edges of the shroud to the radiator makes these even more efficient.

Most properly-designed OEM electric cooling fan arrangements on modern cars utilize a full shroud (to use the entire core surface for cooling), and have a number of large rubber flappers built into the shroud that are opened up by ram airflow at highway speed to increase total airflow through the radiator.

[Dennis C.]

Once again, thanks all for your helpful input... *NM*

[Dick W.]

Re: Off Subject: Engine Driven Fan VS Electric Fan

From one "damebramaged" old phart to another, do you have to use a "puller" fan? A "pusher" fan arangement is more efficient. The staged fans setup that Duke talks about would be ideal. Wire at least one to come on with the A/C compressor. That way you would have excellent A/C at low speeds.

An aluminum Griffin radiator would be the iceing on the cake. Use a 195 to 205 degree thermostat. You should have no problems pulling your camper with this arrangement

[Dennis C.]

Yo Dickie... Somewhere along the line...

...I thought I was led to believe that the electric puller fans were more effecient than the pusher fans. Perhaps I missunderstood. Please confirm my understanding, right or wrong. Thanks, Dipstick

[Dick W.]

Re: Yo Dickie... Somewhere along the line...

Let's try this again. I worked with some engineers several years ago on a project that required quite a bit of air movement. They all were of the opinion that you could push air more efficiently than you could pull it. You do not have the losses from air pulled in from areas that you are not trying to move it through. They were mobile air units utilizing 500 inch Cadillac engines with a fixed wooden/brass aircraft propeller. In excess of 100 decibles noise. Maybe that is what blew all the hair from the top of my head.

[Tracy C.]

Yo Dickie... Sometimes engineers are on drugs...

This link has some good info. If you read down far enough it says tis better to suck than blow. A well fitting shroud is important like any conventional pulley driven set-up.

tc

P.S. can't blame the guys you worked with for using drugs..after all, they were working with you




suck or blow theories exposed

[Dick W.]

Re: Yo Dickie... Sometimes engineers are on drugs.

But Dipstick ain't a runnin' 180 mph. Even iffen he uses "giggle gas".

[Tracy C.]

Re: Yo Dickie... Sometimes engineers are on drugs.

I've heard about that dasturdly giggle gas deed of his. In fact so has everyone else who read Roy's "priceless" article in the last Restorer. I'm kinda jealous through because the only giggle gas I can muster really stinks and does nothing for my vechicular acceleration.

I have fun with it anyway..

[Dennis C.]

You guys oughta charge admission for some...

...of these threads. Thanks again. And what, by the way, is this "giggle" gas you speak of...???

[Dick W.]

Re: You guys oughta charge admission for some...

I just know of rumors of the "giggle gas". It has been rumored that some white headed old phart in the Pacific Northwest used some in a race with the Maryland Missle or was the the Maryland Mucous? I also have heard that it will cause u-joints disintegrate leaving the car owner stranded several hundred miles from home. But then again that is just hearesay cause I left 'fer everyone else.