rear flaps affect cooling?

[bevans6]

I have a little oil leak that I can neither find nor fix.  It puts oil all over the left side of my towed car.  The PO had a big full width rubber flap under the bumper, that I took off when I installed my trailer hitch.  I'm thinking it was there for a purpose, said purpose being to keep the oil and crap off the towed car...   If I put one back on, what would I expect to see as far as an affect on cooling, since the fans exhaust the radiator head down on the MCI.

Brian

[Ed Hackenbruch]

Brian, on my 5A i have mud flaps behind the back wheels and under the bumper i have what some people call a hula skirt or whiskers. It stops oil and rocks from being flipped up onto the car and doesn't affect the cooling as far as i can tell.....i usually run right at or just a hair below 180 most of the time.  It sounds like your oil leak might be from the slobber tubes. Do they go into a catch container?  Mine do and will throw oil on the left side of the car if i forget to drain it once in awhile.

[lostagain]

Yes it would impede the flow of air out of the engine compartment, and negatively affect the cooling. That is the theory anyway. If you still have the flap, why don't you try putting it back on to see what happens. It might be minimal enough that you could keep there. Some guys say that it really increases temp., others don't. I had a friend with a Prevost XL that installed a full flap and it didn't increase his running temp.

JC

[Ed Hackenbruch]

Maybe that is why the PO of my bus did not install a solid flap.

[bevans6]

thanks Ed.  I don't know where the leak is from, but it ain't the slobber tubes!  I got new check vents for them, and routed the hoses to catch cans.  The check valves that were on the vents had been "serviced" at some point by having their insides removed totally...  Reduced the mess by about 50%, but there is still oil accumulating under the chassis from somewhere.  I think it's coming from the alternator, but for the life of me I can't see where.  I figure if I can't fix the problem, I can at least work on making the symptom go away...That being the oil on my wife's car!  

Brian

[Kenny]

Hearing that your radiator blower discharges on top the the engine, then the heated air must then travel around the engine and exit out the bottom of the engine compartment. Unless someone has imperical proof, I would believe that a full length mud flap or air dam just behind the rear tires would create negitive pressures beyond the air dam or in the the engine compartment. Negitive pressure in the engine compartment would in turn increase air flow through the radiators.
Kenny

[bevans6]

The air flap in question is not just behind the rear tires (there are stock flaps there, actually) but at the rear bumper.  I think they will increase the air pressure inside the engine compartment, not reduce it, in that location, and the question is, anecdotally - how bad is it?  So far the answers are not too bad at all..., which is good!

Brian

[Kenny]

A full length mud flap across the bumper would act as an air dam causing increased pressure in the bottom discharge area of the engine compartment which will impede air flow through the radiators. Now if your engine compartment discharge area were out the back of the bus rather than underneath, a full length mud flap across the bumper should have little affect. As JC suggested a full length hula skirt or whisker type to catch the random rock, road kill kidney and oil drips while minimizing an air damming affect would be the better solution.
Kenny

[Just Dallas]

Removed

[JohnEd]

We have businesses here in Eugene that are called "Mill Supply".  They cut conveyor belts to size and they throw away what is left on the roll....40 feet I have seen.  I have a couple pieces maybe 10 feet long.  As you might expect, it is industructible.  It was free to me and it will be to any that wants to stop on their journey N or S thru Eugene. Give me some warning and I can make sure it is still there or get more.  Mud flaps??

I would add that putting a dam on the front of the bus would impede the air flow UNDER the bus and that decreases drag.  I doubt you will see the improvement in MPG in you wallet but maybe it is the principle of the thing ?? 

John

[Chopper Scott]

I have the same problem Brian. I thought of trying one that only covers the rear of the engine bay and not the entire bus. Just a thought.

[bevans6]

My neighbour has a wack of surplus conveyor belting, he uses it as a floor covering on the barn for his race horses.  I guess I will get some and try various things.  the MCI has mudflaps behind the rear axle already, but they aren't full width, maybe 3 feet in the middle under the transmission missing.  I can cut various widths of things and see what happens.

Brian

[eddiepotts]

Things that make you think. I have noticed now on those 95* days we have, my genny will get hot and shut down. It is a water cooled 21kw kabota. I don't know if it should be blowing air across the radiator and out the side of the bus through the vents or pulling air through and sending it across the engine like a car then out the hole in the bottom of the bus. Your belt idea may do the trick, depending which side of the hole I was to put it on, to force air up and across or stop the pressure block of the air moving across the bottom of the bus at 70mph.

[bevans6]

The underside of the bus is generally going to be a low pressure area.  Putting a flap ahead of the hole in the floor should increase the pressure differential, pulling more air down the hole to the underside of the bus.  Airflow along the side of the bus is fairly chaotic, but in general is a high-ish pressure area starting maybe 10 feet from the front of the bus.  the AC condenser on my bus drew air in from the side and down and out  the bottom, aided by a 2 hp fan.

Brian

[luvrbus]

Hope it works for you I do know it will not work on a Eagle behind the drivers or on at the rear bumper been there done that it will raise the temps on a 740 and 8v92 by 10 degrees on a Eagle.


good luck