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Old 03-24-2019, 04:12 AM   #1
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Thinking outside of the (engine compartment) box

In the past decade, anytime I am in the presence of diesel mechanics, I always ask them the same question " which engine is best for a type D bus?" They will often answer "none" because they feel there is not adequate cooling in the engine box. Are there any good solutions for this?
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Old 03-24-2019, 04:30 AM   #2
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In the past decade, anytime I am in the presence of diesel mechanics, I always ask them the same question " which engine is best for a type D bus?" They will often answer "none" because they feel there is not adequate cooling in the engine box. Are there any good solutions for this?
Rear engine buses have the most cooling issues.
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Old 03-24-2019, 06:49 AM   #3
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Rear engine buses have the most cooling issues.
Has anyone ever though of putting a radiator on the roof directly above the engine compartment
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Old 03-24-2019, 10:52 AM   #4
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Has anyone ever though of putting a radiator on the roof directly above the engine compartment
At one time I wanted to put a Nissan L6 motor from a 280Z into my 1984 pickup and replace the L4. To squeeze it in, I was thinking of the radiator on the roof.
Then I bought a Weber carb and an aftermarket long-pipe exhaust header, and I never looked back. She would easy crawl up a 45° incline at 600 RPM with my foot barely on the gas pedal, and I could just feather the gas even at that low RMP, and she would pull strong.
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Old 03-27-2019, 04:23 PM   #5
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You could do it sure. Just would need to build some sort of shielding and housing for it and the hoses. But ductwork underneath the bus might be a good alternative, or even locating the rad to the front if possible!
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Old 03-27-2019, 09:21 PM   #6
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You could do it sure. Just would need to build some sort of shielding and housing for it and the hoses. But ductwork underneath the bus might be a good alternative, or even locating the rad to the front if possible!
The front was my first thought - especially since I could tap into the line for heating, but it would mean a 30+ foot long tube for the antifreeze to run through, and then 30' back. On top of the bus would only be about 9 feet and could be run through the passenger compartment in the corner - well insulated and protected. Is the length a valid fear? Given the brick shape of busses, I think air flow would be better on top of the bus than plastered on the front of the bus. Lay the radiator flat on the roof, but elevate the rear 4-5"....build a simple vented enclose around it. The sun might heat the fluid up to 130 degrees when parked, but in the big picture, this is insignificant to the engine operating temperature.
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Old 03-27-2019, 09:31 PM   #7
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You need to consider the volume that would require pumping. The water pump would need to be strong enough to go upwards and around. If it’s front mounted the length isn’t a concern really. Many of our buses had inside heaters very far from the engine and rad. Same exact concept.
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Old 03-28-2019, 12:00 AM   #8
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You need to consider the volume that would require pumping. The water pump would need to be strong enough to go upwards and around. If it’s front mounted the length isn’t a concern really. Many of our buses had inside heaters very far from the engine and rad. Same exact concept.

Would an auxiliary electric water pump be useful? Maybe I am overly paranoid but I am concerned also about the physical safety of a radiator up front..minor fender benders...people backing up, etc. although it would be really cool - but time consuming - to build a "nose" for a type D pusher bus...to help some of the aerodynamics
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Old 03-28-2019, 12:26 AM   #9
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Biggest problem with RE bus cooling is getting the air across the radiator. A lot of HP is used for the cooling fan. If putting a radiator on the roof it would work best to use a short radiator mounted vertically across the width of the roof with a scoop to direct the air through the radiator. Mounted horizontally electric cooling fans would be needed like a roof mounted AC condenser.

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Old 03-28-2019, 05:27 AM   #10
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Biggest problem with RE bus cooling is getting the air across the radiator. A lot of HP is used for the cooling fan. If putting a radiator on the roof it would work best to use a short radiator mounted vertically across the width of the roof with a scoop to direct the air through the radiator. Mounted horizontally electric cooling fans would be needed like a roof mounted AC condenser.

Ted
Thats what I was thinking - a 6 or 7' wide radiator mounted across the width of the bus....raised 4-5" in the back with some kind of shroud/scoop to direct more air to it..and a fan (probably a couple of fans) to provide air at lower vehicle speeds. I may have to use 2 radiators - I have not seen a 7' wide radiator.
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Old 03-28-2019, 09:35 AM   #11
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Just a thought but...what about installing a pair of high cfm electric fans?
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Old 03-28-2019, 09:36 AM   #12
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If you're relocating the radiator, it would cool better being mounted on the front. Air pressure would be highest there vs being mounted on the roof and you'll actually have negative air pressure if you mount it in some spots.

You could rig up a few electric fans to be behind it in place of a hydraulic or mechanical fan. Biggest issue would be running 30 ft of pipe to and from the radiator and keeping it all from leaking. Your mechanical water pumps can put out a lot of pressure. Try dead heading the upper radiator hose sometime with the thermostat removed.
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Old 03-28-2019, 10:06 AM   #13
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The Britten V1000 motorcycle placed its radiator under the seat and used ducts to move air to it, claiming a reduction in drag without loss of cooling performance. it stands to reason that you could put the radiator anywhere as long as you too crate a duct system to move air. However, given the aerodynamic realities of a transit style bus, it seems unlikely that you'd gain anything by relocating it.
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Old 03-28-2019, 12:28 PM   #14
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what about a large scoop or fin to divert air into where it is needed?
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Old 03-28-2019, 01:00 PM   #15
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A radiator on the roof in a closed loop has a siphon-effect as the coolant returns down to the engine, and has no bearing on the pump. For every ounce of coolant missing in the top of the radiator, load is added to the pump. So it seems to me.
My air conditioning would cool so much better when my vehicles' AC radiators were not in the sun. Any shadow made them work so much better. The rooftop AC radiators on my bus were sun-exposed, and are getting new metallic shade-covers. If they work up there, so should your rooftop one. But I hate the added height (but love the AC) so I would put the engine radiator in the front, if it added overall height to my bus.
Negative pressure is, as mentioned above, always a possibility, especially if the engine radiator will be placed behind something else on your roof, i.e. an AC radiator setup, a roof-rack full of stuff, etc.
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Old 04-07-2019, 04:16 AM   #16
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Every OEM that has ever built a rear engine bus has tried all sorts of ways to cool a rear engine bus. Suffice it to say, no one has been 100% successful. If you drive a rear engine bus it isn't a question of if you are going to overheat so much as when you will overheat.


Flxible, Kenworth, Gillig, and MCI all tried some sort of roof mounted scoop to force more air across the raditor.



Crown solved the problem with their mid-mount engine by using a radiator that is 3' tall, 6' wide, and at least 8" thick.



Setra tried solving the problem by adding additional radiators for greater cooling ability.



The basic problem with cooling a rear engine bus is you are working against physics. The air along the outside of the engine compartment when you are going down the road is a low pressure area. The engine compartment is a high pressure area. Moving air "uphill" to go across the cooling fins of a radiator takes a LOT of HP. Whether it is directly off of the engine via a belt or hydraulics or a passive system using just electric fans it is going to take 35-40 HP to turn the fans enough to cool the engine.


The problem exacerbates exponentially when you start to boost the HP and you keep your foot buried as you go up a hill.



Moving the radiator to the front bumper so the air the bus is pushing through will have to push through the radiator is probably the best way to never overheat. But at that point you are relying on pumps and electric motors to keep the coolant cooled and circulating enough to keep the engine cool. VW had a lot of problems with their water cooled rear engine Vanagons because the coolant circuit was prone to getting air locks.
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