Fuel Mileage

[nealnfl]

Just drove a 2006 XL-II 1300 miles from Missouri to Florida. The best average mileage I could get was 5.3 MPG. Obviously there is something not right. I would think 6.5 should be average. Seems I have to get into the turbo more than any other coach I have driven. Any ideas for Detroit Diesel to check on?

[BrianE]

#1 suspect would be a turbo leak. A clogged injector might be suspect but would check the clamps and turbo case first. Don't know your experience so pardon if you considered use of generator.....Typically about a gallon an hour.

[Mark3101]

How fast? I don't get much more than that when running 70-75 mph. I can get better by slowing down of course.

[merle&louise]

Nealnfl,

Is the 5.3 the reading from the ProDriver or are you calculating it the old fashion way: total miles / gallons used. If you are using the ProDriver be sure to set it back to zero.

Brian brings up a good point, are you running the generator with 3 CruiseAirs running?

What are you towing?

How fast are you driving?

All of the above have to do with mpg.

I must admit though I get 7.2 mpg towing a Honda Pilot driving 65 mph and 7.7 not towing anything. If I slow down to 60 mph and not towing a vehicle I can get 8.0

[merle&louise]

Speaking of fuel mileage - has anyone noticed that the price of diesel is EQUAL to the price of REGULAR unleaded gasoline!

What's up with that? Remember when it was .50 per gallon more expensive!

I noticed that equality of price at two different truck stops in my home town. The truck stops are locally owned (not Flying Js or TA, etc.)

[jack14r]

The 06 would have the EGR engine and if you drove 75 mph or more 5.3 would not be too far off,I would check the codes in the message center display,but since you did not say anything about a CEL I doubt you have a problem.

[gmcbuffalo]

Tuga I can remember when diesel was cheaper than regular gas.

[Jon Wehrenberg]

We as observers have noted fuel consumption discussions ever since we owned our first coach. It was an 87 shell, 8V92, weighed 41,000 and over almost 15 years delivered a constant 5.6 MPG. My typical interstate speed was 62 MPH towing 3400 pounds. In 1990 when we bought our first coach and started to go to rallies owners were complaining about mileage while at the same time going to DD to get the power turned up from 475 HP to 500. Prevost was eventually convinced to up the HP on new coaches. So back then owners wanted hot rod performance but were unhappy with mileage.

Our second coach is a 96 shell, Series 60 weighing 46,600 towing 3400, 6700 or 5300 pounds. Driving the same 62 MPH highway speed, started around 8 MPG and when they started changing the fuel forumlation mileage went down and is now consistently 7.5 MPG. I still have log books with every single gallon of fuel I have ever pumped into the coaches recorded along with the mileage and location. I can also point out when I was able to buy diesel almost anywhere for $.899 per gallon.

Later coaches started getting heavier, especially those with slides, the EPA standards for the engines changed, and I noticed most owners drive at higher speeds. It all adds up. There is a huge penalty in MPG as speed increases. That is the single element totally under the control of the driver. There is a point in MPH where the mileage falls like a rock. When I have run hard in the 70 to 75 MPH range I think it costs about 1 MPG. The other factors which influence MPG are weight, over which we have a degree of control, but limited. The terrain also is a big factor because no matter how long the downhill run, it never compensates for the fuel used going up the hill. Regardless of how the coach is equipped with AC, the more AC is used the lower the mileage, but not as much as running into a 15 knot headwind for example.

I have learned a few things over the years regarding mileage. The nozzle will not always click off when filling at the same point. As a result checking mileage on a single tank is going to produce inaccurate mileage figures. I base my mileage on annual readings and the Pro-Driver and the fuel pump calculations when allowing .5 GPH for the generator hours come out almost exactly. I reset the Pro Driver at my service intervals of 5000 miles so I am looking at the equivalent of about 3 or 4 refills. At that point whether fuel is calculated or read from the Pro Driver the numbers come out the same unless there is a significant use of the generator which is not reflected in the Pro Driver, but is reflected in the cost of fuel to run the bus.

One point I will always make mostly to help myself put this into perspective is our use of fuel and its cost is chump change compared to the big picture. On newer coaches depreciation and loss of earnings on invested capital represent the largest ongoing expense associated with ownership and the difference in the cost of fuel from 5 MPG to 8 MPG even at today's prices is not much more than a rounding error when looking at the cost of ownership. I don't think we should worry about our MPG or fuel cost at the pump. I do seriously believe however if all things are constant and we see a significant change in what normal fuel consumption is then we should take note and try to determine the cause.

Regarding Neal's original post, if he drives 20,000 miles annually (a lot based on the average use by POG members) his cost for fuel at 5.3 MPG and $4.00 per gallon is $15094. At 6.5 MPG it costs $12307 or a savings of $2787. If Neal's annual usage is less than that that difference shrinks proportionately. Anybody care to guess the depreciation on a 2006 XL or the loss of earnings on the capital invested in that coach?

[phorner]

I pretty much see the same mileage as Jon.

Although we don't have that as extensive a history, we consistently get between 7.4 and 7.7 MPG. Not much variation over the last 20k miles or so.

I typically drive at 65 MPH and always tow our Hummer, although it is the lighter, H3 model. The last time I weighed our bus, it hit the GVWR right on the nose at 48,900.

[merle&louise]

I noticed today in my home town that a truck stop had diesel priced $.26 BELOW the price of unleaded gasoline!

Does anybody know why this reversal has taken placed?

I'm happy to see the reduction in price, but I was just wondering why?

[pump7167]

i only wish i could get the mileage that's been described. the best mileage i have been able to average was 4.6 driving 70-75

[Sid Tuls]

I ave about 6.3-6.6 on this trip so far heading to Wisconsin from Calif. That's going 65-70 on an average.

[BoaterAl]

I think your mileage is going out the exhaust pipe at that average speed

[Kevin Erion]

I just finished 5400 miles going 64MPH towing a 3/4 ton pick up at about 7000lbs. I get 6.2 to 6.4 mpg with the DDEC IV. This is running 2 cruise airs off the inverters and the dash air all the time.

[jack14r]

I don't know what pump is driving but it must be a DDEC V or VI if not he should have the charge air cooler inspected for cracks.

[truk4u]

Eat your heart out boys, 8.10 on this leg.

8359

[Ledo]

Tuga I had heard that after the last big run up in oil prices, Exxon and maybe others had or were in the process of building a refinery or refineries that focused more on diesel output. Maybe only certain types of crude oils generate more diesel then other lighter condensates or visaversa. I don't believe you can refine any barrel of crude and make it all come out diesel because diesel is only a small percentage of total usually but I may be wrong. More diesel refined and into the market equals lower prices.

[phorner]

Of all the expenses related to bus ownership, fuel is at the bottom of my list to care about.

I'll bet on average, with the typical mileage driven by us on an annual basis, I spend more on tires, batteries, maintenance (belts, hoses, air bags, etc.) and fluid changes than I do on fuel.

[merle&louise]

Tuga I had heard that after the last big run up in oil prices, Exxon and maybe others had or were in the process of building a refinery or refineries that focused more on diesel output. Maybe only certain types of crude oils generate more diesel then other lighter condensates or visaversa. I don't believe you can refine any barrel of crude and make it all come out diesel because diesel is only a small percentage of total usually but I may be wrong. More diesel refined and into the market equals lower prices.

Lee,

I hope what you are saying is true. I remember back in the days before low sulfur diesel, diesel was .50 to .60 per gallon cheaper than gasoline. I am looking at my rack sheet (daily prices from my jobber) and the difference between diesel and gasoline is .0725 before any taxes. The tax on diesel is .1705 higher than the tax on gasoline. So that results in .2430 higher cost per gallon. Take a look at the street prices and you will see a .50 to .60 HIGHER price for diesel. The extra cost goes directly into the pocket of the truck stop owner!

Also, did you ever notice that the customer is forced to pay a higher credit card price on diesel BUT NOT ON GASOLINE!

I'd like to hear that explanation. Even using Obama math you can't make that dog hunt!

The truck stops are ripping us off - plain and simple!

[Danss]

Tom, Tuga and the rest of you fine gentlemen I won't post my milage I get on this ORPHAN BUS because I don't want youall to get depressed. Youall will be wanting to trade down just to attempt to equal my milage!!!

[merle&louise]

Never believe anything that a guy from Mississippi tells you!

[rfoster]

post it Dan, post it.

[Danss]

If you insist. 8.5 mpg on fairly level road towing Chev. trailblazer at approx 68 to 70 mph. I would think I would get 9 possibly without tow. Hilly country reduces milage to about 7 to 7.5. Tuga, you should get excellent milage because no matter where you are you are going downhill when you head home!!!! Houma is real close to the EDGE!

[Jon Wehrenberg]

At 5 mpg, and $4.00 per gallon each mile costs $.80.

At 7 mpg, and $4.00 per gallon each mile costs $.57.

Regardless of the cost it will be a rare owner who spends anywhere near as much for fuel as he is spending for depreciation or lost earnings on the invested capital.

Got tires on your bus? Figure the cost of those per year using six years of life as a basis. Got insurance? Add that in. Air bags, figure their cost of replacement. If you have slides add in the cost of replacing seals on an annual basis. Do you pay for storage when you don't use your bus? Add that in. I'd be willing to guess the fixed expenses of ownership exceed what the average owner pays for fuel annually. If you are making payments pull out the interest and add that to the annual cost. By the time you get done facing reality you will quickly realize it is more reasonable to drive the wheels off the coach and pay the price of fuel than it is to park the bus because fuel is getting expensive.

[Ledo]

Today while changing out a tag wheel seal we found out that the guide pins on the brake rotors have begun to seize up and have not been releasing and sliding on that one wheel. Brake pads are good every where else except for that wheel. Replacing pads and cleaning up pins for smooth movement and hopefully get a little milage from the dragging wheel repair.

[Jon Wehrenberg]

Everybody's mileage is going to be influenced by a lot of factors. The speed you drive (or the headwinds you encounter) may likely be the greatest influence, but hills, the weight of the toad, the weight of the coach, the outside air temperature, the AC load, all play a part in mileage.

BTW, don't think if you don't have OTR your air conditioning of the coach is not going to affect your mileage or more appropriately your fuel consumption. For identical AC loads the only factor which will vary the amount of fuel used is the efficiency of the power source which could be the engine driven OTR system, or the inverter powered roof air or the generator powered Cruise air.

[Pete]

Or engine powered dash air.

[TerryM]

Just back from a little summer road trip. H3 weight about 53,000 lbs, Lexus about 4,500 lbs., OTR running entire time, 872 miles (western PA, western NY, Ohio), cruise set at 64, ambient temp between 87 and 97, averaged 8.1 mpg according to data from SilverLeaf. I haven't fueled and checked mileage. Is mpg data from DDEC fairly accurate?

[phorner]

I believe the DDEC information is probably the most accurate as I think it is measuring the actual flow of fuel through the injectors.

If that is, in fact the case, then variables such as generator run time, use of the Webasto system, etc. are taken out of the equation as well as the variability of filling to the exact same "full" mark every time.

My mileage is typically 7.1 to 7.7 MPG, even a couple of 8.0 reading on rare occasions, and I'm comfortable with that number as fairly representing my fuel economy as it very closely predicts the gallons needed at fill up.

[merle&louise]

If you insist. 8.5 mpg on fairly level road towing Chev. trailblazer at approx 68 to 70 mph. I would think I would get 9 possibly without tow. Hilly country reduces milage to about 7 to 7.5. Tuga, you should get excellent milage because no matter where you are you are going downhill when you head home!!!! Houma is real close to the EDGE!

You can't get any closer to the edge without getting your feet wet!

[jack14r]

I have found both the DDEC data and the Silverleaf to be very accurate.

[truk4u]

Hey Dano,

If you finally left the Casino, you better get off that throttle, I think I just got ya!:p

8366

[rfoster]

Trukster

Dandy Dan was the big winner tonight!

[RussWhite]

This seems like a good place to ask this question - which I have tried to find, but can't. Does anyone know how ProDriver measures fuel consumed? I am curious if it is actually measured directly with flow meters like in a diesel boat - one meter for flow from tank and another for return flow, with the difference being fuel consumed. Or, could ProDrive be inferring fuel used by length of fuel injector pulses or something similar.

Thanks,
Russ

[johnklopp]

I believe it has to be the injection timing, pressure etc. enabling the flow to be calculated using the same computer that controls the injection cycle.

[jimshoen]

I am getting 7.4 MPG in the mountains out of Reno. Do not tow. 47,000 lbs loaded

[johnklopp]

Tom,

Had to put my foot in it to pass you after POG 10 in Austin.

Mileage from Nashville to Austin was 9.85 with an average speed of 61.9 MPH with cruise set at 65-67 MPH.

Mileage from Austin to Nashville was 9.35 with an average speed of 63.4 MPH with cruise set at 70-72 MPH.

Taking into account the overall MPG reduction, I lost around 1 MPG on the Austin to Nashville Leg.

Got an unexpected new message on the Pro Driver, WARNING EXCEEDING 77 MPH

[truk4u]

John,

You had the hammer down when you went by me and that's great mileage your getting. We pulled into Loves near Dallas behind Doug Cox and bought fuel for 3.39!

[rfoster]

Paid $3.49 @ Flying j in Knoxville today at the truck pumps with RV card. Flying J has resumed discount with RV card and you can pump first then pay. Like ole times.

[phorner]

That's cool, Roger!

By reducing the "hassle" of dealing with the truck pumps, Flying J has converted me into a return, regular customer.

For a while, I avoided them as it was too much work involved to simply fuel the bus. I didn't necessarily mind parting with that much cash.... just didn't think they should make it difficult for me to do so!

[travelite]

JohnKlopp,

Those are great numbers. Any idea what final drive ratio you're running?

[GDeen]

Whisky Tango Foxtrot John?

How do you get mileage up in that range? Need you to come tune my fuel system or give me driving lessons.

[Jon Wehrenberg]

John has used his heat transfer engineering skills to create a negative pressure area in the front of the bus, and when combined with the positive pressure area he has set up in the rear (he takes air from the front and puts it in the back) it is the equivalent of always driving with a tailwind.

That plus he has a coach that weighs less than 20,000 pounds, combined with not towing, and using his generator to power the electric motors on the front axle wheels and he can get such god mileage. He learned the generator fuel does not get shown in the ProDriver so he now has the ability to show such good mileage.

There may be another explaination, but that's the best I can come up with.

[rahangman]

Paul, good reply, but it jogged my mind. I am thinking, how much of this crazy world can we blame on something such as you said, "I dont mind parting with that much cash, just didin't think they should make it difficult for me to do so". I think it is a core problem with the USA today

[johnklopp]

It’s simply physics!

Many things go into mileage as have been discussed on the forum. Driving style, coach weight, weight of a toad, headwinds, terrain etc. all contribute to a varying degree.

Two things are not as obvious but are some of the largest contributors to low mileage. Air resistance requires large amounts power to push the coach thru the air. Jon was correct indicating a low pressure area in the front of the coach would be beneficial. Unfortunately my experiments with creating a vortex in front of the coach have been unsuccessful.

The last item is tire rolling resistance. Tire rolling resistance is simply the force a tire must overcome to roll. A coach’s engine has to burn fuel to overcome this force to move. The less rolling resistance, the less fuel an engine burns to make the tire go round and round.

Reducing rolling resistance is a goal for those who want to achieve an improvement in fuel efficiency.

Once the tire is rolling, the rubber sidewall in a tire exhibits flex sometimes called hysteresis. Hysteresis is the main cause of energy loss associated with rolling resistance, and is attributed to the elastic deformation of the rubber.

As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy as heat rejection. That’s precisely why you can measure your tire temperatures at rest stops and quickly see if any of them are underinflated.

Load: As the load decreases, so does rolling resistance (near proportional). As load decreases, so will the deformation/deflection of the tire; less deformation means less energy loss.

Inflation Pressure: As pressure increases, rolling resistance decreases. This is attributed to less deformation and bending in the tire due to the increase in pneumatic stiffness. However, the relationship is not linear. In the typical operating inflation pressure range, an increase of 2 psi should improve rolling resistance approximately 1.5%-2%. Conversely, low inflation will cause excessive deformation and increased rolling resistance.

The bottom line in my opinion is tire inflation pressure contributed greatly toward the mileage I was able to achieve. Before departing Nashville, all of my tires were inflated to 110 PSI cold. Before departing POG 10, I increased the inflation pressure to 115 PSI cold.
Obviously the great ride our coaches are known for was compromised.

Perhaps by POG 11 I will have had time to build a clip on plastic nose cone to not only protect the bus but reduce aerodynamic drag.

[travelite]

John, that's great info, thanks. Given how exceptional your fuel mileage numbers are, you have to pardon a bit of skepticism. So here goes... :) Have you confirmed the accuracy of your DDEC mpg figures the old fashion way - miles driven as read from the odometer divided by gallons pumped at the filling station? Do you know what you final drive ratio is?

[travelite]

I'm sure most folks have seen the attached Caterpillar document on RV fuel mileage. If not, enjoy!

[Jon Wehrenberg]

David,

I cannot verify the accuracy of other ProDriver mileage figures but I can say mine is quite accurate. I know the miles per hour it displays when I set the cruise control is accurate when compared to my speedometer (which I calibrated using 10 miles worth of mile markers when I installed the speedometer) and my GPS. I have records of every gallon of fuel I ever pumped into my coaches for 21 years so I can pick any time period and pull out generator usage (based on the generator service logs) but not webasto usage. As near as i can determine ProDriver is really accurate.

I do not reset my ProDriver except for my service reminder periods of 5000 miles, and during those periods, the number seem to jive. I can say with conviction that measuring fuel purchases for a tank or two is a waste of time because my ability to fill to the same tank level is almost impossible. I have pumped at the slowest setting on the truck pumps and had the pump click off and had the normal filler fuel puke. I have then gone to an automobile diesel pump and gotten as much as 30 gallons more into the tank. So I calculate my mileages using a year or two of refueling figures with an estimate of generator usage pulled out of the fuel amounts.

[tskrodzki]

Wish the was the case in MA. High octane gas is 3.83 with Diesel at 4.23 recently dropped to 4.12 but the upcoming holiday is driving the price back up:mad:

[Kenneth Brewer]

John has used his heat transfer engineering skills to create a negative pressure area in the front of the bus, and when combined with the positive pressure area he has set up in the rear (he takes air from the front and puts it in the back) it is the equivalent of always driving with a tailwind.

That plus he has a coach that weighs less than 20,000 pounds, combined with not towing, and using his generator to power the electric motors on the front axle wheels and he can get such god mileage. He learned the generator fuel does not get shown in the ProDriver so he now has the ability to show such good mileage.

There may be another explaination, but that's the best I can come up with.

Sounds about right.