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Author Topic: Radiator fan consumes over 10% of engine HP!  (Read 8565 times)
Mex-Busnut
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« on: June 08, 2011, 06:19:59 PM »

Dear Friends,

I was reading where the radiator fan on my 6V92TA can consume as much as 40 horsepower! The engine is supposedly set up at 330 HP. Many modern vehicles have temperature-controlled clutches on the fans, or electric fans. Is there anything a crazed busnut can do in this department to reduce drag on the engine, and thus liberate some HP and increase fuel economy:

Here is a picture of my setup.

Thanks in advance! 
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Dr. Steve, San Juan del Río, Querétaro, Mexico, North America, Planet Earth, Milky Way.
1981 Dina Olímpico (Flxible Flxliner clone), 6V92TA Detroit Diesel
Rockwell model RM135A 9-speed manual tranny.
Jake brakes
100 miles North West of Mexico City, Mexico. 6,800 feet altitude.
robertglines1
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« Reply #1 on: June 08, 2011, 06:33:23 PM »

Really don't think 40 hp is bad. Even elect is going to require power generation. Or hydraulic you have to drive pump. Is your bus running cool enough under a hard climb? You wouldn't want to run less if it isn't. Nothing more dependable than belt drive! No pump to fail or electric motor to burn out; always happens at a bad time. Simple is sometimes best and most dependable in long run.
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
luvrbus
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« Reply #2 on: June 08, 2011, 06:35:58 PM »

A Horton 2 speed fan clutch, electric fans will do you no good,but you will be wasting your money with 6v92 and a Horton very seldom will you be able to run on low and set down when you get a price for one they are proud of it
 I always thought a 6v92 -330 hp used around 50 hp

good luck
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HighTechRedneck
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« Reply #3 on: June 08, 2011, 06:41:54 PM »

A couple more considerations on it.  

When you need the horsepower the most is generally the same time that your engine needs the most cooling capacity.

And diesel pushers generally need most of the fan's capability at cruising speed.  Unlike vehicles with a front end radiator, the forward motion doesn't help move air through the radiator.  In fact it can make it harder to get a good flow into it.  Hence the various scoops and air dams that some people use to help with engine cooling while driving.
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robertglines1
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« Reply #4 on: June 08, 2011, 07:07:13 PM »

Dr. Steve    Your thinking   that's good !    Mechanical is more dependable for your travel plans just listening to your post you plan on desert and mountains. will max out your cooling system. Much easier to find belt on road than elect motor or hydraulic motor or pump.   and cheaper.   Bob
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
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« Reply #5 on: June 08, 2011, 07:42:07 PM »

Dear Friends,

I was reading where the radiator fan on my 6V92TA can consume as much as 40 horsepower! The engine is supposedly set up at 330 HP. Many modern vehicles have temperature-controlled clutches on the fans, or electric fans. Is there anything a crazed busnut can do in this department to reduce drag on the engine, and thus liberate some HP and increase fuel economy:

Here is a picture of my setup.

Thanks in advance! 

The issue of parasitic fan loss, and available alternative fan solutions, have been things that troubled me since day 1 of owning my bus - because the OEM fan setup was gone, replaced by (gasp) an electric setup.

After a ton of research and fan calculations (I'm a mechanical engineer myself), I have concluded, and MCI seems to agree with me, that a fan only needs its max capacity less than 10% of its time. A fan's power consumption goes up approximately cubic to its rpm. In other words, that 40hp fan would only consume 5hp at half its rpm. At 5hp, the fan would still retain a good portion of its CFM, because as you decrease CFM, you also have less resistance through the rad, which makes flow easier.

OEMs have to cover the worst driving situations: uphill, full throttle, AC full blast, 105 degree and high humidity. As private owners and engineers, we can choose what driving situations to cover.

My bus has never overheated, even climbing through BC rockies in 90 degree weather. How? Because of the relatively little 6V71 and manual transmission. On a 6V92 or 8V92 with an auto, it's a completely difference story. You're now dealing with heat rejection of a much larger engine, more hp, torque converter, and turbo intercooler. Electric fans are pretty much out of the question. But an electro-magnetic fan drive that operates in partial mode, consuming 3 - 5 hp, may perfectly suffice 90% of the time.


My rad is just about shot, and I'm reluctant to pay $1600 to get it rebuilt (because my OEM fan is missing). I've taken on a brave cooling project: an F350 radiator from the 7.3 Powerstroke era, along with two electric fan assemblies (4 fans total, plus one pusher) out of Nissan Altimas. For anyone who's interested, or in serious doubt that it'll work, I'll beposting an update in the next month or so. My preliminary calculations say it will work. Worst case, I'll be using my misters a lot  Grin
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TomC
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« Reply #6 on: June 08, 2011, 08:18:43 PM »

If I had your setup, I'd install the 2spd air operated fan clutch.  I lopes around using about 5hp to gently pull air through at all times (by eddy current-like a slipping motor) then when you need it, it engages to normal fan speed.  I have a gear drive on my Vdrive that doesn't allow for the two speed.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #7 on: June 08, 2011, 08:49:59 PM »

  The fans used are generally crude, more akin to clubs, not exactly a nice twisted aerofoil prop like an airplane or wind tunnel fan with hig aspect ratio blades. You could get some gain, maybe as much as 20% or more with a decent blade. As suggested, a prop/fan directly driven by an electric motor would be more efficient.

  But the only time that fan will ever see 40 HP is in low gear, on the governor, at sea level. Once the Bus is moving, induced airflow will reduce the load, at cruising speed with lower RPM will reduce load, and higher altitude with lower air density will reduce load. Its probably only pulling 15-20 HP or less sailing down the highway once it slows down and has air blowing through it.

  I would start with making sure air flow is unrestricted, make sure the fan has good bearings, that its balanced (both in weight as well as loading,that each blade is pitched the same), blade face is clean/polished. Its doubtful you would gain much through engineering changes to ever witness much at the pump.
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RJ
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« Reply #8 on: June 08, 2011, 09:05:22 PM »

Dr Steve -

Fan and cooling issues have been beaten to death time and time again on both major bus bulletin boards.

Simple answer?

For the OEM powertrain, it's hard to second-guess the factory.

Fuel economy vs the cooling fan?

It's the weight of the operator's right shoe that has the biggest effect, everything else is minor. 

Pushing a vehicle that has the aerodynamics of a brick down the highway is going to take fuel - wind resistance is your second-biggest enemy.

With 10 gears to play with, it's going to be easy to keep the 6V in it's "sweet spot," thus lowering the cooling load on the radiator/fan.

Don't forget the engine's also cooled by the lubricating oil - make sure you're running straight 40 wt - and that the oil cooling system is functioning properly.  Additional cooling here, thermostatically controlled, might be a more thoughtful approach to your non-issue.

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #9 on: June 08, 2011, 09:18:06 PM »

Buses don't induce air the fan works more at cruising speeds several nice variable pitch thermo control fans on the market for buses I had one on the Eagle not cheap for a 32 in 16 blade but they work
.Boomer has a nice electric fan setup on his Eagle but he done a lot of research and spent some bucks for his Cummins engine and I have doubts his would work on a 8v92. Cat has great info on what hp,size,cfm and type it takes to cool their engines in any application they have a hydraulic system listed by flow,pressure,HP and sizes but no electric fwiw and RJ pretty well hit the nail on the head

good luck

  
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« Reply #10 on: June 09, 2011, 09:24:20 PM »

My old Crown Supercoach had two rather very large belts pulling the big fan.  A knowledgeable mechanic once said the two could easily handle 50hp.  The coolant capacity was 32 gallons and the oil capacity was 44 quarts.  (if faulty memory serves)  HB of CJ (old coot)  Smiley Smiley Smiley
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Mex-Busnut
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« Reply #11 on: June 10, 2011, 06:55:02 AM »

Thanks to all of you for your most enlightening comments. I would like to get 100 miles per gallon on my little bus, and pay 10 cents a gallon for diesel...
 Grin

Dr Steve -

Don't forget the engine's also cooled by the lubricating oil - make sure you're running straight 40 wt - and that the oil cooling system is functioning properly.  

Mr. RJ et al:

The previous owner (a professional tour bus operator) has been running straight Mobil 40-weight diesel oil in this bus. Is this the best oil for it? Also, how often do you guys recommend the oil and filters be changed? I need it to last me trouble-free another 30 years, at which time, good Lord willing and the creek don't rise, I will be 83 years old, and ready to inherit the bus to my most awesome grandsons...

Thanks in advance!

« Last Edit: June 10, 2011, 06:59:36 AM by Mex-Busnut » Logged

Dr. Steve, San Juan del Río, Querétaro, Mexico, North America, Planet Earth, Milky Way.
1981 Dina Olímpico (Flxible Flxliner clone), 6V92TA Detroit Diesel
Rockwell model RM135A 9-speed manual tranny.
Jake brakes
100 miles North West of Mexico City, Mexico. 6,800 feet altitude.
TomC
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« Reply #12 on: June 10, 2011, 07:10:48 AM »

Depending on your kind of driving, I would either just change the oil twice a year or every 10,000 miles. 

When I was driving, I found through oil analysis (available at Speedco oil change outlets) that 12,000 miles was the magic number.  Amazing to that the 3406B Caterpillar did not need any oil added during that time.  As compared now to Detroits DD engines at 50,000 mile oil changes!  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #13 on: June 10, 2011, 07:31:47 AM »

Buses don't induce air the fan works more at cruising speeds

  Then their blowing the air the wrong way.   
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HighTechRedneck
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« Reply #14 on: June 10, 2011, 08:26:09 AM »

Buses don't induce air the fan works more at cruising speeds

  Then their blowing the air the wrong way.   

When in motion (without factoring in ambient wind conditions), the airflow down the side is perpendicular to the radiator grill.  That flow actually works against the fan's effort to draw air in.  The higher the speed, the more work is required to pull air in.

Why don't buses blow the hot air out through the radiator instead?  I'm just guessing here, but perhaps if that much air was being pushed outward while at cruising speed, that same perpendicular air flow that resisted inflow, when confronted with a high volume of air pushing out into it would form back pressure restricting outflow.

I have wondered why they didn't put the radiator on the back of the bus and have the fan(s) push the air through it with the aid of the natural vacuum on the back like they did the AC condenser on my RTS.

I've always thought the roof top scoop on the old Flx's were a great idea, the next best thing to a front mounted radiator.  It seems like you could really make a difference combining that with a thermal clutched fan and exhausting the flow out the back.  But maybe the extra drag induced by the air scoop consumes more power than it saves.  I don't know.
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