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Old 09-17-2012, 10:43 AM   #43
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The six diesel is the dodge cummins, although the new ones are less efficient than the older ones, one can still get fifteen mpg out of them. Jim
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Old 09-17-2012, 10:44 AM   #44
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That is fifteen towing. Jim
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Old 09-17-2012, 10:59 AM   #45
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Well what if we could calculate the best possible miles per gallon assuming 100% efficeincy in converting fuel to motion. This would give us a number that you will never get better than. If we could get every bit of energy to the wheels what would the number be? Would it be 20MPG or 25MPG etc.? We don't know what we are shooting for. We know we can't get better than 100% but we have no idea of knowing how good 15MPG is in terms of efficiency.

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Old 09-17-2012, 11:08 AM   #46
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Mine are all so old the taxes are less than $100/yr. They are also all paid for. Maintenance is done by me. True that if you are the average person and you hire everything out and you are paying insurance, taxes and a loan in a nanny state like many northern and west coast states then having several vehicles is expensive. It depends on your situation whether it is cheaper to have a dedicated tow vehicle. I live in the country and I need a daily driver for a 70 mile round trip and a bigger vehicle to tow with and do farm related chores where I need something big with a lot of room. I would have a farm type work truck whether I had an Airstream to tow with it or not.

Perry
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Old 09-17-2012, 11:27 AM   #47
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Well what if we could calculate the best possible miles per gallon assuming 100% efficeincy in converting fuel to motion. This would give us a number that you will never get better than. If we could get every bit of energy to the wheels what would the number be? Would it be 20MPG or 25MPG etc.? We don't know what we are shooting for. We know we can't get better than 100% but we have no idea of knowing how good 15MPG is in terms of efficiency.

Perry
Consider regular driving: You can go 60MPH in a car that is getting 18MPG and you can go 60MPH in a car that is getting 42MPG. The differences will show up in weight and acceleration and various other parameters - of course. But the point remains -- they both go 60MPH and they get very different mileage.

With my current 'Burb, I bet I can go 0 to 60 with my trailer hooked up in about 12 seconds. Maybe even less - it really goes when I step on it. Now just suppose I was willing to trade off some of that muscle for more mileage? That's the sort of thing I am wondering. It seems as though the car makers are aiming at one target and one target only with their TVs - maximum power. (Ecoboost might be the exception.)

Are there any 6-cyl diesels in new models of trucks/SUV? I don't know of any.
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Old 09-17-2012, 11:30 AM   #48
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Problem is, I think, there is probably no way to do a calculation for maximum efficiency to work back from. For one thing, you have done no change when you move a trailer and return it to the same elevation. So maximum with no friction losses you could do it with no energy. The energy used is all to overcome losses.

Not sure about the conversion of fuel to energy. Maybe the second law of thermodynamics gives a maximum based on T2-T1, but then if you had a really good process and great materials you could change T2. I guess that is the basis of why a diesel is more efficient. But what is the limit??

Pulling a trailer for a lot of miles is just going to be expensive. Something we all deal with in different manners.
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Old 09-17-2012, 11:33 AM   #49
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Are there any 6-cyl diesels in new models of trucks/SUV? I don't know of any.
Isn't Dodge (RAM) still building the Cummins powered pickup?

Looks like it from their website: http://www.ramtrucks.com/en/2012/ram...ty/powertrain/
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Old 09-17-2012, 11:35 AM   #50
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OK, I found the Dodge 6-cyl diesel for 2012.
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Old 09-17-2012, 11:43 AM   #51
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Yes, Dodge is still running a six cylinder Cummins diesel. It's grown up to a 6.7 liter now. It has fallen behind lately in mileage and performance compared to its V8 diesel competitors, but it's still a viable engine.

The problem is, all of the new diesels are suffering from new emission laws which make them even more complicated and delicate and expensive. They still get better mileage than the gasoline models, but their high cost of fuel per gallon has reduced the fuel cost savings.
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Old 09-17-2012, 11:50 AM   #52
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Big difference - outbound & inbound legs

Two weeks ago I experienced my best towing mileage with my '06 LLY Duramax -- 16.2 & 16.6 mpg on two successive days of 163 & 100 miles. Conditions of the drive were what mattered. They were cool days without air conditioning and I was doing very soft driving between 55 & 60 mph. Terrain was gently rolling. I let speed bleed off at each hill and didn't use cruise control. Each day's drive was short enough that I didn't get impatient & pick up the speed.

I averaged about 10 mph higher returning all in one day with air conditioning on a week later and got 12.4 mpg. This all is using the onboard computer and I'd take the actual numbers with a grain of salt.
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Old 09-17-2012, 01:17 PM   #53
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Problem is, I think, there is probably no way to do a calculation for maximum efficiency to work back from. For one thing, you have done no change when you move a trailer and return it to the same elevation. So maximum with no friction losses you could do it with no energy. The energy used is all to overcome losses.

Not sure about the conversion of fuel to energy. Maybe the second law of thermodynamics gives a maximum based on T2-T1, but then if you had a really good process and great materials you could change T2. I guess that is the basis of why a diesel is more efficient. But what is the limit??

Pulling a trailer for a lot of miles is just going to be expensive. Something we all deal with in different manners.
I think the math is probably the easy part. In other words, if you know the masses and speeds and resistances, you can determine how much energy is required. But, knowing that is theoretical and doesn't much help in finding a practical solution. By practical, I simply mean - this existing engine with this existing chassis and this existing gear set and so on.

If I look at our little Ford Escape, it probably has enough power and torque to pull our trailer, BUT the chassis is probably not sprung right for an 800# tongue weight - right? In other words, that might be the right engine, but the wrong chassis (or at least the wrong axles).

Suppose there was a big demand for towing 25 foot trailers like mine, and an Escape type model was made with let's say heavier axles. Would I maybe get my 15MPG?
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Old 09-17-2012, 01:20 PM   #54
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A couple comments -
Ethanol - It reduces fuel mileage due to Lower energy content, all reference material I checked show about 62% the energy of gasoline on a per pound basis. A spark ignition engine can make more power on alcohol due to its high knock resistance but it takes more it, i.e. you have to run the engine richer. This is why alcohol powered race cars, like sprint cars etc, have very high compression ratios but run huge carb jets.

Speed - The horsepower to overcome aerodynamic drag goes up as the cube of the speed increase. I.E. if you double your speed the power to overcome aero drag goes up 8 times. Going from 55 to 70 requires 2.6 times the aero power = lower mileage.

Note I did not say the total power goes up as the cube only the power to overcome drag. There are other items like friction in drivelines, rolling resistance of tires etc, most of these go up only as direct function of speed increase so the overall increase in power doesn't go as cube function but at higher speeds aero drag is the major portion.
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Old 09-17-2012, 01:47 PM   #55
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Interesting Topic...

In a prior life I Workamped in Europe.
My rig was a 1996 BMW 328i Touring(5spd Manual), and I pulled a single axle 20' Camper. I was all over Europe, from Italy to Norway, and I put about 5000 miles on this setup, and kept a pretty close eye on the fuel consumption via the onboard computer.
18 to 23mpg(Imperial Gallons) was the spread towing. The car would average 26 to 30mpg solo.
This pic was taken on a trip going down to work in Italy in summer, and the next pic was the return trip in December...
It was a lot of fun!




I guess my point is that a reletively lighweight but powerful(190hp) tow car and a lightweight camper did not do much better than some of the figures I have seen here!

Our 1984 Airstream 345 with a carb'ed 454 gas motor did between 7 and 8.4mpg and it weighs in at about 16,500lb...
My old 454 injected Suburban that weighs almost 6000lb will barely do 12mpg on a similar freeway run...

My experience would suggest that you run and maintain what you have... it takes a ton of money buy somethingnew, and you will never get it back!
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Old 09-17-2012, 02:16 PM   #56
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I didn't read the entire topic, but another option would be to consider mods that increase the power of the engine. Even with those mods, if you still drive efficiently, you should get better mileage. Probably not 50% better than what you have now, of course. But a better intake or exhaust, depending on how restrictive your current setup is, could get you a couple extra MPGs. Much cheaper than a new vehicle, too.
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