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Author Topic: Cooling - mud flaps  (Read 1017 times)
chuckd
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« on: July 02, 2013, 07:57:36 AM »

I was looking at the bus cooling system, while I was ruminating about my leaving the card board thermostats on, and something does not make sense.  The engine driven fan sucks air through the side mounted fan, and the air is then blown over the engine, and out the grill on the other side, at least I think it should do that.  However the path to that grill is convoluted and filled with a turbo charger, batteries etc.  My bus has (had) a 3/8s thick reinforced rubber mat across the entire back of the bus.  Now it looks like that would block air from escaping out that direction, so got my trusty sawsall and it came off.  Now I am thinking maybe not so smart, maybe that was designed to keep a high pressure area their so the air would cross over the engine.

I think I read years earlier, that removing this was a good idea, but when I searched I could not find anything.  So okay to remove the rear mud guard, or did I just do another self inflicted problem.

Thanks

Chuckd
Stillwater Mn
35 foot Prevost
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belfert
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« Reply #1 on: July 02, 2013, 08:08:30 AM »

I recall that mud flaps across the very rear actually cause cooling issues.  A lot of the GMs had factory installed flaps to help cooling, but they were forward of the engine, not at the rear. 
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
Emcemv
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« Reply #2 on: July 02, 2013, 09:25:18 AM »

i have read on this forum that the mud flap needs to be mounted directly behind the rear wheels, creating a low pressure area under the engine, helping to  exhaust the hot air, helping with cooling.

Bruce
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Bruce & Nancy Fagley
1973 MCI MC-7 Combo Freighter
450HP DD 8V-92T 2000 Reman
HT 740 Allison
Woodbury CT.
Purplewillie
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« Reply #3 on: July 02, 2013, 09:46:29 AM »


Just after purchasing our bus

And after I removed the rear flap
Mark
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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
Purplewillie
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« Reply #4 on: July 02, 2013, 09:51:36 AM »

Flap directly behind the rear wheels is correct , not at the rear bumper
Mark
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Mark & Char
1976 P8M4905a 8v71 v730
British Columbia Canada
usbusin
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'60 PD4104-4355(sold) Now Freightliner Conversion




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« Reply #5 on: July 02, 2013, 09:56:30 AM »


Flap directly behind the rear wheels is correct , not at the rear bumper
Mark

I know this is true for GM's.  Is it correct for Prevost's?

GaryD
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Gary D

USBUSIN was our 1960 PD4104 for 16 years Ustruckin' is our 2001 Freightliner truck conversion
bevans6
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« Reply #6 on: July 02, 2013, 10:31:48 AM »

Air will probably come in both sides (the radiator side with the fan and the grill side) and go out the bottom of the engine bay when the bus is at speed. The rear sides of the bus become a quite high pressure area and the bottom of the bus is a quite low pressure area, made more so by things like a flap in front of the engine bay, the height of the bay itself, and so on.  The rear mounted flap is usually just to protect the towed car, it will increase the pressure under the bay and reduce the flow of air.

Brian

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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
chessie4905
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« Reply #7 on: July 02, 2013, 10:48:19 AM »

 As most 2 cycle DD's like to leak oil, at least a little, the fan turns it into mist and it gets deposited on rear of coach or on towed item. This is why rear flaps came into use.Some companies make a broom type of flap to still allow air to pass a little. They eventually get oil coated so you can rub your head on it when getting under there.@#$&%. Probably no one noticed the running hotter issue, since it was only a little in most cases. Many of the behind the axle flaps rotted off or were removed during servicing. You can usually still see the mounting metal underneath, at least on GM's. Many of the conversions have had the horsepower upgraded=more heat. Makes shroud sealing and behind the axle flap use more important.
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GMC h8h 649#028
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chuckd
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« Reply #8 on: July 02, 2013, 11:20:45 AM »

Thanks guys, my Tracker gets rust proofed every trip, even with the mud flap.

Chucked
Stilleter mn
Prevost
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Jon
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« Reply #9 on: July 02, 2013, 12:03:18 PM »

I've had three Prevost coaches, an 87, 97 and an 06. I took the full width flaps off on the 87 and 97. I never had a cooling problem and couldn't see an advantage to the flap other than to add some bling because both had a polished stainless strip that ran full width.

I am not removing the flap on the 06. The air flow as designed is clearly to pass over the engine before exiting the engine area. There is a couple of baffles beneath the fan and they must remain in place. So the air from the fan has to pass over the engine and then exit either out the passenger side, passenger side bottom or out the louvers in the rear doors. With the flap in place it contributes to the negative pressure across the rear of the coach and encourages air to flow out the rear door louvers.

On an early vintage Prevost I would remove the flap, but since I don't design coaches my opinion is worth every cent you paid for it.
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Jon

Current coach 2006 Prevost, Liberty conversion
Knoxville, TN
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« Reply #10 on: July 02, 2013, 02:54:11 PM »

Thank you for this thread, I've heard many here allude to how important the mudflap on the rear of a GM bus is but never had anyone clarify that the flap should be IN FRONT of the engine.  I have a background in aerodynamics and used to work with air cooled cars ALOT,  until now the flap seemed counter-intuitive.   This finally makes sense to me now.

I'm headed to the shop to relocate my uniflap, now I must figure how to keep my already eternally oily towd clean.

Thanks for the excellent posting
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RJ
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« Reply #11 on: July 02, 2013, 03:08:09 PM »

Thank you for this thread, I've heard many here allude to how important the mudflap on the rear of a GM bus is but never had anyone clarify that the flap should be IN FRONT of the engine. 

NHB -

You might find this thread informative, too:

http://www.busnut.com/bbs/messages/233/31201.html

FWIW & HTH. . .

 Wink
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RJ Long
PD4106-2784 No More
Fresno CA
paul102a3
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« Reply #12 on: July 02, 2013, 08:52:37 PM »

My Prevost has warning labels all over the engine compartment stating that you must not remove the mud flaps and air dam located behind the rear wheels except for service.   
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2001 Prevost XL II
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