Jackjagt
S.W. Ontario
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Joined: 08/23/2004
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It seems that the Diesel, class "A" RV manufacturers have slipped one by us.
I am referring to the inherent poorer fuel economy of a rear radiator Diesel pusher RV, compared to the traditional side mounted radiators that were the norm a few years ago.
The move to rear radiator pushers was because of significant cost savings and to suggest "progress" in pusher RVs.
But buyers of rear radiator units may have noticed poorer fuel economy, compared to their weight.
The reason is that air passing thru a rear radiator has already been heated (to some degree) by its passage past the engine, something that did not happen with a side radiator.
The Diesel of course is a "heat engine" as are all internal combustion engines. Thus power is generated by the pistons proportionate to maximum and minimum temperatures.
Maximum heat (and thus pressure) is created by the combustion of Diesel Fuel. Before the next power stroke, the combustion chamber is cooled by the circulating cooling fluid. BUT the cooling by the rear radiator can never equal the cooling by a side radiator! Because significantly warmer air (prewarmed by passage next to a hot engine)passes thru the rear radiator.
So now you know why your mileage is not as good as your old sideradiator coach.
Sad but true....
* This post was
edited 11/12/09 05:52am by Jackjagt *
Life's a Trip!
Greyhead & a cute Brunette
07 Safari Cheetah 36PPD
02 red VW Jetta TDI toad
FMCA F226315,
Ontario OverLanders
Michigan Knights
Skype "merrieyacht'
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wolfe10
Texas
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Joined: 10/08/2000
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LOTS of generalizations here.
Factors to consider in addition to radiator location-- and absolutely, a thermostatically controlled fan WILL save fuel over a "constant on" fan:
GCW-- definitely on the increase along with size and number of slides.
EPA specs
Gearing-- recent coaches have taller gearing that in many cases precludes 6th gear at an economic speed.
Frontal area-- many coaches are quite a lot taller as well as wide-bodied.
More HP
Brett Wolfe
1993 Foretravel 36' U-240
Cat 3116, Allison 3060
Caterpillar RV Engine Owner's Club: www.catrvclub.org
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Dynasty40
Northern California
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Joined: 02/07/2008
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I got 9.3MPG on my last 3800 mile trip towing a HHR. Side radiatoried 40'Dynasty......Dennis
Is radiatoried a word....
Dennis and Debi
Monaco Dynasty Baron 40PFD
Towing a Chevy HHR W/
ReadyBrute
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427435
Rochester, Mn
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Joined: 11/12/2005
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I don't own a DP but the pro's and con's are interesting between a side radiator and a rear radiator.
A side radiator usually uses a hydraulically driven fan instead of a belt driven fan that the rear radiator will likely have. The hydraulic drive will be less efficient and can cause a nasty fire if a hydraulic line fails. Remember that both the hydraulic drive and belt drive can be intermittent or "clutched" for efficiency. Also, there are more things that can go wrong with the hydraulic fan drive.
The rear radiator may have warmer air flowing through it, but that "warmth" comes from "cooling" the engine.
The rear radiator can also get "oiled" up if the engine's breather tube is not routed well------which brings up a question. Aren't the newer diesels required to have crankcase breathing systems that re-cycle the fumes??
I suspect, when the dust settles, it becomes a Ford vs Chevy (or Cat vs Cummins) thing. If I were buying a DP (and I'm not), I would probably go for the simplicity of the rear radiator and be sure the breather tube is routed well.
Mark
2000 Itasca Suncruiser 35U on a Ford chassis
2003 Ford Explorer toad with US Gear brakes,
ReadyBrute tow bar, and Demco base plate.
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Cody47
Madison, SD
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Joined: 10/05/2002
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Our 40' Tour (2008 EPA specs) is rear radiator and has a clutch fan system (Freightliner chassis, Cummins 400hp ISL engine), so the fan runs only when needed. So far, our coach which has a high profile, gets an honest 8 mpg overall (this is the average for the first 18,000 miles of use) while pulling a toad. Based on conversations with others with the side radiator, this seems pretty good.
Cody47
2008 Winnebago Tour 40TD
2009 Chevy HHR Toad
http://fulltime-rv.blogspot.com/
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spitfirepete
Great Outdoors RV resort
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Joined: 11/17/2003
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Mine is rear radiator with clutch fan...07 model with no slobber tube, has recirculation system...Radiator is still very clean...Engine temp never increased noticeably even climbing out west...8.7 MPG average on this cross country trip towing....In flat FL I get close to 10 MPG....
Things have changed.
Peter and Linda
2007 Mandalay Presidio ISC
1975 Triumph Spitfire toad
2007 Saturn Vue toad
Bichon and Cocker (spoiled puppies)
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Popsie
Livingston, TX, USA
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Joined: 04/04/2003
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IMO, the primary difference is when you have to get at the engine to do something.
They may be out there, but I've never seen a rear radiator setup that made it easy to get at the engine and accessories.
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Desertcat921
HERMISTON OR
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Joined: 09/08/2003
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Nobody seems to inject the wieght into the equation. As more wieght is added tha mileage is less.
1988 MCI Widebody 40' Coach Conversion, 8V92TA Silver w/ Allison 740
Auto Transmission. 480 Watts Solar, Hughes Satellite Internet W/ Motosat Datastorm, Dish TV. One Cat named Monkey..
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Deen
Vancouver, WA
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Joined: 12/07/2000
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Desertcat921 wrote:Nobody seems to inject the wieght into the equation. As more wieght is added tha mileage is less.
Not necessarily!! It depends on the gearing and engine as well as the driver. I've seen 40,000# DP's with ISM's get better mileage than a lighter unit with an ISC Cummins.
I'm watching my VMSpc closely right now to determine the best cruising speed. 1650 rpm is almost exactly 60 mph, at that speed I get between 10 and 14 mpg on the "level". That depends on the wind and small changes in elevation. Torque peak is 1400 to 1700 rpm (1200 ft. lbs) with the Banks setup. Stock is 1050 ft lbs at 1400 rpm so I'm running 250 rpm over the normal torque peak which should be the best as most diesels seem to get the best mileage 200 rpm over torque peak.
If you have a bigger engine and higher gearing the torque peak may be at lower rpm, but the gearing is set so you're going faster.
Some people accelerate faster, some don't. I'm sure if I was following Brett I'd accelerate faster than he does, if I followed him long enough my fuel mileage wouold go up too. Just too many variables to make a broad generalization!
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Deen
Vancouver, WA
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Joined: 12/07/2000
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wolfe10 wrote:
Gearing-- recent coaches have taller gearing that in many cases precludes 6th gear at an economic speed.
I'm sure a lot of DP owners will run into this if they ever lower the speed limits to 55! I can't even get into 6th until 54 mph so every little hump would cause a downshift even in economy mode.
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