Kevin510

Bad, And I Mean Bad, MPG

65 posts in this topic

Hi everyone.

I finally got to take my rig out on a pretty long trip and was surprised by the mpg that I got. It is a 2003 Newmar Scottsdale on a Workhorse chassis. It is 37' 9" and weighs about 19,500 lbs. with us in it. We pulled our Jeep Commander on a 2,200-mile trip a few weeks ago.

When we left Amarillo, we had to fight a terrible head and cross wind (about 50 mph). We drove east to OKC trying to drive anywhere from 55 to 70 mph to find that "sweet spot" where the coach wouldn't have to downshift to fight the wind and slight hills. We fueled in OKC and got about 4.6 mpg. I wasn't totally surprised by this due to the wind. We continued our travels east to Nashville, Tn. I drove most of the trip at 65 mph but did try to slow down for a few tanks but it didn't seem to help. The best I could get was 5.5 mpg.

The best I have ever gotten was 6.9 from Amarillo to Okmulgee, OK. driving about 62 to 65 mph. It has a brand-new air filter.

The exhaust seems to be okay and not clogged or anything like that. No foul smell like a clogged catalytic converter. There is no check engine light and the engine seems to run great. It has plenty of power, never gets hot or misses. About the only thing it has ever done is have a low idle at times but that seems to have cleared up recently. Is this normal for a rig of this size? Is there anything I can do to get some better mpg?

I am not expecting a lot, but I think that 5.5 is a bit low.

Any and all thought are welcome.

Thanks

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With your 19,500 lbs you also have to add the weight of your toad, which has to be at least 4,000 lbs doesn't it? I am assuming you have the Allison 5-speed transmission. My rig (Workhorse/Allison) and trailer weigh a total of 20,500 lbs and I set the cruise at 62 MPH. I turn off the cruise when climbing a steep hill and allow the motor to gently downshift. I rarely get over 3,000 RPMs at any time. I get 8.1 MPG at that speed. Speed up to 65 and I get 7.0. So when you say you are driving 62 to 65 MPH you can see what the difference is. You weigh 3,000 lbs more than me.

Head winds have a huge effect on mileage. So can small winds. So can driving west. I think your mileage is a little low. I would try a tank at 62 PMH and see what you get and then go from there. Also a trip without the toad might tell you if its weight is the issue.

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Using the cruise control improves the mileage as well. I get about a mile per gallon more when I use the cruise as much as possible even going up and down hills. I have the Allison 3000 tranny.

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If you slow down to 55-57 you will get the best mileage.You should see an increase of about 25 %.

I drive my diesel pusher 32 foot towing a Silverado 1500 and get between 10 and 11 mpg going 58-60 mph.

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I have a 8.1 Vortec Chev engine in my W22 workhorse under a 33 foot rexhall and tow a 3000 pound saturn at 55 mph the legel towing speed and I consistently get from 8.1 to 8.5 depending on weather and terrain.

Bebop Bill Forrest

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We made a recent two and a half month trip out West. We drove a total of 4940.4 miles and used 533.978 gallons of gas for an average of 9.25 MPG in our 2004 Airstream Land Yacht, 30 ft. motor home with one slide and towing a Toyota Corolla. The trip took us from southern Indiana to the west coast and back to Melbourne, FL. Our speed was typically 60 MPH and I also took the rig out of cruse control when aproaching a hill to prevent premature downshifting. We were mainly on I-44, I-40, I-17, I-10, and I-8 with a side trip from Albuquerque, NM to Cortez, CO. We used the generator, but probably no more than a total of five hours.

This rig has a Workhorse chassis, GM tranmission, and 8.1-L GM engine.

Sam

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Thanks for the replies everyone. I do use the cruise until it comes time to climb a hill. I also figure the weight of my toad has a lot more to do with it. I looked it up and the Jeep weighs about 5200 lbs. I had been considering selling it to either go to a diesel or something smaller but I guess I will keep it for a while longer and try some different speeds. I am also going to try and pull my parents CRV on the next trip and see if that makes a difference. It weighs about 2000lbs. less than the jeep. I am also going to check the odometer the next time I get it out.

What do you guys think about changing the plugs? I doubt that they have ever been changed and I have about 55k miles on them. Any other ideas are welcome. Does anyone know if they make a tuner for this chassis?

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Kevin,

It wouldn't hurt to pull one of the plugs and take a look to see if it is really sooted up. Black soot could mean that it is running too rich and a hotter plug might help. I am sure there is a tuner made for your 8.1. If you have a GPS you can check your speedo with it. Since our odometer is off (about 2 10th), I drive by the GPS for my speed.

Herman

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What chassis do you have? It seems to me that your RV plus your toad is exceeding the GCWR (Gross Combination Weight Rating).

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What chassis do you have? It seems to me that your RV plus your toad is exceeding the GCWR (Gross Combination Weight Rating).

I am on the W-22 with a 26,000 lb. gcwr. The jeep actually weighs 5047 lbs. with a full tank of fuel. But we always plan to pull it with only about a half tank at the very most. I will have to take them both out to some scales to be totally sure but by my calculations, we are sitting around 24,500 lbs. with the jeep connected.

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You are running a big heavy rig you won’t get great mileage if you don’t drive a little slower. I would try to find where it shifts into your top gear and set my cruise just fast enough it stays in the top gear most of the time. You will have it downshifting to go over hills ect. But you are better off just staying in top gear. I do this on my coach it isn’t the same because it is diesel but the principal is the same. You could see what Banks has to give you more torque to help it hold top gear longer when you hit a hill.

http://bankspower.com/products/show/122/68

Bill

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The biggest hindrances to "good" MPH, assuming your engine is running right, are head winds and going too fast. All you can do is reduce your speed.

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You are running a big heavy rig you won’t get great mileage if you don’t drive a little slower. I would try to find where it shifts into your top gear and set my cruise just fast enough it stays in the top gear most of the time. You will have it downshifting to go over hills ect. But you are better off just staying in top gear. I do this on my coach it isn’t the same because it is diesel but the principal is the same. You could see what Banks has to give you more torque to help it hold top gear longer when you hit a hill.

http://bankspower.com/products/show/122/68

Bill

Thanks for the input Bill. I am really considering a Banks system. And I got you on the driving in top gear. That is why I drive about 62 mph. If I drive any slower, it will downshift right into 3rd at about 4500 rpm and it sounds like a jet taking off. I am just going to slow down a bit more and try pulling something that weighs a bit less than our Jeep and see if that makes a difference.

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Hi Kevin, Been thinking about your MPG issue and I think I would run some injector cleaner through the engine. I have used Lucas injector cleaner(5 oz per 25 Gal) myself and add some to the fuel one a year to keep injectors working well. I have always been a little concerned about the injector valves and ethanol drying out the O ring seals.

Dirty injectors can have an adverse effect on fuel usage.

I was a little slow about mentioning it with the air filter and plug post !!!! Rereading your post and see an idle issue and that it has cleared some recently. The fuel blend is changed in the winter with a reduction in ethanol percentage.

Rich.

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Kevin...you said in a previous post...."and it sounds like a jet taking off"...

This noise you hear may be the clutched fan in front of your engine. When your water temperature climbs the clutch in the fan engages and it sounds like you have described. But if the fan is always engaged it could be contributing to your fuel mileage issue as it is causing an unnecessary load directly on your engine.

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Kevin...you said in a previous post...."and it sounds like a jet taking off"...

This noise you hear may be the clutched fan in front of your engine. When your water temperature climbs the clutch in the fan engages and it sounds like you have described. But if the fan is always engaged it could be contributing to your fuel mileage issue as it is causing an unnecessary load directly on your engine.

Good Point Big Dog !!!

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The clutch fan is working as it should. I was just joking about how loud the thing is, but your right Richard, it gets even louder when the clutch fan engages. I did run some injector cleaner through when I first got it but it was the cheapest stuff I could find.

I think I will try for a little better quality product and pull some plugs in a few days to see if they fouled. I am still considering the Banks system but the more I read, the less I am inclined to get it.

Most of the reviews I have read state that the power gains are good but economy gains are minimal. According to the Banks site, the power pack can add a bunch of power, but only about a 1/2 mpg gain.

It would take a LOT of driving to off set that $3000 price tag.

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I think it is interesting that the speed you are running to stay in top gear is basically the same as I use. I run 62-65. I can’t get it to shift into 6th under 62 and I find running just a little more rpm helps keep it in 6th. I think the reason to by the Banks is to improve drive ability. I didn’t by a motor home with the thought there would be a payback down the road.

Bill

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I've had an older P-30 chassis RV with the Chevy engine a few years back. The best thing I ever did was put on a Magnaflow muffler that opened up exhaust system.

The noise of the engine reduced. The heat it created reduced. The quickness of the rig improved and the mpg rose .75mpg. We were able to pass better and climb hills much much better.

The research I found suggested a couple of things....1) Banks may improve all of the above, but at $2000 to $2500 for the system, your break even point might be outside the life of your RV. 2) Increasing the air intake, like using a K&N filter, may be offset since the engine limits incoming air based on computer calculations. 3) A RAM air intake may be effective in cooling the air prior to entry into the engine which helps with power and mpg. 4) The muffler change was the least expensive expenditure for the most performance/fuel economy gain. 5) EVERYONE got better gas mileage than I did. :)

Jim

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I think it is interesting that the speed you are running to stay in top gear is basically the same as I use. I run 62-65. I can’t get it to shift into 6th under 62 and I find running just a little more rpm helps keep it in 6th. I think the reason to by the Banks is to improve drive ability. I didn’t by a motor home with the thought there would be a payback down the road.

Bill

I am not sure I understand what you mean by a "payback down the road" I was referring to the Banks system and its cost to benefit ratio. Not the cost of the rig its self.

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Kevin, in my opinion you have to make some changes. 5.5 mpg stinks!!!

I have 65K miles on my '04 Chieftain, 39 ft on and extended wheelbase W22 chassis. I usualy get 7.2 mpg pulling a Suziki Grand Vitara 3500 lbs and get 6.5 pulling my 4500 enclosed trailer & sandrail. That is out here in the West where the land isn't very flat. Back east I was getting about 0.5 mpg more. With the Suziki and full tanks I weigh in at a little over 26K. I usually drive 60-65 mph. Since day one I track my fuel, milage and generator hours to calculate mpg's in an Excel fspreadsheet.

In '06 I installed Brazel's UltraPower and Cold Air filter modification. My mpg went up about 10%. Then about a year later the country and CA went with Ethenol gas and the milage dropped back down about 10%. I like the Ultrapower because it gives about 60 hp more and keeps the Allison in 5th gear longer and I pull the steeper grades at 50-55 mph instead of 40-45 mph and one gear higher than before the mod.

When Brazel's install the UP, they first analyze all the stored engine parameters, and can tell by the fuel trim values and other things if the engine is running "normal". My guess Kevin, is that your engine is not running optimum and you have a lot of soot in your tail pipes, although all the WH 8.1 seem to run rich. Give the Brazel's guys in Centralia, Wash a call ...Jon or Steve. Their website is HERE. If your in Texas, call Oem'y Performance, he installs UP too. Website here.

Good luck,

Bill

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I have a larger and newer rig than you have but these numbers might be of interest. Mine is a 2007 Itasca Suncruiser on the Workhorse W24 chassis/ I have the Allison 6 speed tranny. Over the lift of the motor I have averaged 6.7 mpg while fulltiming. I weigh 23,500 pounds and tow a 3,500 pound Suzuki Grand Vitara. That makes me 27,000 pounds overall. I too have found that speed and wind makes the greatest difference. I have averaged 9.28 mpg while driving the Natchez Trace where the road is flat and the speed limit (enforced) is 50 mph. I have also hit 5.5 mpg many times (maybe 10 - 15). I have been in the Rocky Mountains where my speed is 35 - 40 with heavy climbing and still gotten 6 - 7 mpg. The speed is more important than the mountain climbing for my load. I would guess that you are running a little lower mpg than you should but it might be that your older motor doesn't have the horsepower and tuning that my newer rig has. Also, the difference on a 1,000 mile trip at today's gas prices between 5.5 mpg and 6.5 mpg is only $100. You really can't spend much money on Banks or other systems and get a payback. Just drive a little slower and avoid full throttle starts and enjoy your motorhome.

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I have a larger and newer rig than you have but these numbers might be of interest. Mine is a 2007 Itasca Suncruiser on the Workhorse W24 chassis/ I have the Allison 6 speed tranny. Over the lift of the motor I have averaged 6.7 mpg while fulltiming. I weigh 23,500 pounds and tow a 3,500 pound Suzuki Grand Vitara. That makes me 27,000 pounds overall. I too have found that speed and wind makes the greatest difference. I have averaged 9.28 mpg while driving the Natchez Trace where the road is flat and the speed limit (enforced) is 50 mph. I have also hit 5.5 mpg many times (maybe 10 - 15). I have been in the Rocky Mountains where my speed is 35 - 40 with heavy climbing and still gotten 6 - 7 mpg. The speed is more important than the mountain climbing for my load. I would guess that you are running a little lower mpg than you should but it might be that your older motor doesn't have the horsepower and tuning that my newer rig has. Also, the difference on a 1,000 mile trip at today's gas prices between 5.5 mpg and 6.5 mpg is only $100. You really can't spend much money on Banks or other systems and get a payback. Just drive a little slower and avoid full throttle starts and enjoy your motorhome.

That makes me feel better to know that my mpg is some what normal. We havent used this one long enough to really guage our overall mpg. Especially while towing. And your right about one thing, regardless of mpg, we are just going to use it as often as possible.

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Here's the scoop.... use Iso-Heat Year around as directed... as stated you used the cheapest... Iso-Heat is isoprophol, not methanol. In the summer, it offsets the damaging effects of ethanol fuels. (Sold in Walmart).

Next have your rig weighed at a ralley w/ toad or a moving & storage scale. Weigh EACH WHEEL Separately & note them. Armed with individual wheel set weights on each axle, use the highest for all tires on that axle... Front axles & rear will differ. Set pressures from chart noting single or dual. Take your time... It's important !

Have all fluids at normal range... Propane , all waters, groceries & folks. Note your CCC# Cargo carrying Capacity... bet you are over that. Find a tire pressure chart... Good Year, Bridgestone, whatever & set your pressure every morning pre trip !

Run EXACTLY THE FUEL RECOMMENDED IN YOUR CHASSIS ENGINE MANUAL... High Test actually isn't rocket fuel but burns slower than 87. You don't need add-ons! Find a shop with a $20,000. Scan tool, not Car MD. Have a diagnostic done. It can read a faulty Coolant Temperature Sensor which will adjust fuel flow incorrectly. (Scan all data streams & Sensors)

All of this will save you money, I promise. Do a little bit at a time...

The weight & tire pressure calculations will remain the same until you change something in the coach.

Let us know,

Gary

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