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Old 07-27-2014, 09:27 AM   #15
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InfoGraphic: Actual Fuel Economy of Diesel vs Gas Towing

We should, but i doubt there is much difference in modern gas v. Modern diesel engines.

I doubt that the difference is one percent net one way or the other.

Diesels reached the top of their game in the 90s. Since then unreasonable emission expectations have badly hurt their economy and reliability.
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Old 07-27-2014, 09:34 AM   #16
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I think that the emission control standards of the 90s were more than clean enough for gas and diesel, and the stuff done since then is a net looser.....

But with that said,,,, I seriously doubt that modern diesel engines are easier on the environment than modern gas engines.
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Old 07-27-2014, 09:39 AM   #17
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Diesel has another economy edge other than BTU content. Diesel engines are more efficient because of the higher compression. They can extract more energy as a result of the higher compression. BTU content is not the only factor but it is a factor. The EPA putting ethanol in the gasoline does not help the BTU content of gas.

Everything on a diesel is twice as big and heavy because of the higher compression. They are also about 4 times more expensive to fix. There are also more systems to deal with especially with the new diesels. If you get a German made anything and maintenance costs will be even higher than an American made diesel. 20 yrs ago when Diesels were much simpler and diesel fuel was cheap to buy they were probably a good deal. If I want an expensive hobby, I would own a diesel. If I want to turn the key and drive with a couple hundred dollars of maintenance and year, I will drive a gasser.

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The real answer to the question lies in the energy content of diesel v. Gasoline. Diesel has 13% more for a given volume.

This is going to be the primary factor in a logical approach to to discerning the true economy of gas v. Diesel powered trucks.


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Old 07-27-2014, 09:51 AM   #18
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I prefer diesel over gas for heavy hauling. I also keep a couple of old diesel trucks on the place just in case. If diesel or gas becomes unavailable or cost prohibitive I will run 100% bio diesel I did some calculations a couple of years ago, I can plant 12 acres of soybeans/rape seed or something similar and produce more than enough bio to cover my needs for a year.

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Old 07-27-2014, 09:53 AM   #19
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The compression ratio would be factored into overall efficiency. I contend that a modern gas and a modern diesel will be within one percent net in efficiency.

The engineers have worked very hard on getting the most efficiency possible out of modern engines gas and diesel alike.

Compression ratio makes less difference proportionally as it increases.
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Old 07-27-2014, 09:54 AM   #20
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Can you convert the stuff to biodiesel yourself though?

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I prefer diesel over gas for heavy hauling. I also keep a couple of old diesel trucks on the place just in case. If diesel or gas becomes unavailable or cost prohibitive I will run 100% bio diesel I did some calculations a couple of years ago, I can plant 12 acres of soybeans/rape seed or something similar and produce more than enough bio to cover my needs for a year.

Aaron
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Old 07-27-2014, 10:18 AM   #21
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Can you convert the stuff to biodiesel yourself though?

Perry
Yes...

There is a guy down the road from me that has run a Rabbit Diesel pickup (remember those?) for the past 25+ years on straight veggie oil. He uses dino diesel to get it started and warmed up, then swaps over to the veggie. He was getting his oil for free from the various fast food joints around town. He would strain it to get the crunchies out, then store it in a heated tank. He also had some sort of tank heater on the truck. You can always tell when he goes by, smelled like french fries or fried chicken. He is not a very happy camper anymore, the restaurants are now getting paid for their used oil.

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Old 07-27-2014, 01:29 PM   #22
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Does anyone have any knowledge as to why it would cost more in a chevy diesel vs a ford or dodge? Or, does anyone have any real world experience with this? It seems to be a drastic difference and I don't understand why a chevy would get reduced mpg in comparison.

I have been looking at diesel Chevys and this is an important factor. Do I need to rethink things?
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Old 07-27-2014, 06:38 PM   #23
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Does anyone have any knowledge as to why it would cost more in a chevy diesel vs a ford or dodge? Or, does anyone have any real world experience with this? It seems to be a drastic difference and I don't understand why a chevy would get reduced mpg in comparison.

I have been looking at diesel Chevys and this is an important factor. Do I need to rethink things?
Is that really a difficult question to answer for yourself? Not all vehicles are the same, and neither are they're MPG ratings. Same goes with maintenance factors and cost of ownership.
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Old 07-27-2014, 07:20 PM   #24
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A few random thoughts.

A straight six (liked the Cummins) is inherently balanced whereas a V8 is not. So, part of the longevity of the Cummins might be due to smoother running. (this is true in gasoline engine designs as well).

I would expect to see higher mpg on 27' and shorter trailers as the total weight in motion is considerably less that those with current 31' trailers like our Classic at 10,000 pounds GVW versus a 25' at 7,300 pounds GVW of the 27' at 7,600 pounds GVW.

So when I see similar mpg with my rig at a much higher combination weight, then I think my diesel combination is more efficient than a rig pulling a much lighter combination weight.
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Old 07-27-2014, 07:27 PM   #25
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InfoGraphic: Actual Fuel Economy of Diesel vs Gas Towing

Weight makes little difference in economy in highway driving.

Weight once moving is not a hinderance except as it relates to increased tire friction which really isn't a huge drag.

Now, some more energy is lost as heat in braking with heavier loads.

The short way of saying this is that the energy required to tow a 7500 lb trailer v. A 10000 lb trailer is not even close to proportional. Most towing energy is expended pushing air.

(In stop and go a heavier trailer will make a bigger difference with regard to economy)

An even shorter way of saying this is that say we have two identical trailers, even weight, one twenty feet long, one thirty feet long, the two trailers will tow at very near to identical economy.
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Old 07-27-2014, 07:31 PM   #26
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Energy consumed going up hill is recovered going down, except that lost to braking heat or exhaust brakes.

Engine drag and chassis drag is more or less constant,,, or close to constant,,, either up hill or down.
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Old 07-27-2014, 07:40 PM   #27
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The Cummins used in Ram trucks started life as a truck engine designed for smaller medium duty trucks.

Due to the traditional layout of medium duty trucks an inline six fit the chassis better than a V8 diesel so these inline diesels were the ones that received the most development.

There were heavy and medium duty diesels offered, and many of them were quite good, but they have mostly left the scene in American trucks.

I think that Cummins motors are the best of the pickup truck diesels not so much because of them being inline sixes, but because their engineering and execution is better.
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Old 07-28-2014, 10:23 AM   #28
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InfoGraphic: Actual Fuel Economy of Diesel vs Gas Towing

Several of the diesel statistics are true but when I gets down to mpg there is a 30-35 percent betterment with diesel; however, from a fuel economic standpoint, diesel has been 0.40 higher in my area for years. That is a 10 percent difference. Calculate that out and in most situations a diesel has to get a least 2 mpg more to break even with a gasser just on fuel cost. If a urea engine, the benefit is even lower.

The primary argument for diesel is with larger trucks hauling heavy loads and fuel storage of diesel. Used to be durability and torque but those two are matched closely now with gassers. Point on durability check out how much the new high pressure fuel injection systems are that are used on many diesels. They run about $10k for the Bosch one and have a lifespan of about what a gasser is rated.

Urea does not have to do with mpg but it must be figured in as a cost for operation with the fuel.
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