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Old 05-23-2022, 04:20 AM   #1
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How can I improve gas mileage - Damon Intruder 367

We have a 2004 Damon Intruder 367 with a Ford V-10 gas engine, mileage on unit is about 37,500. I have been getting 7 to 7.5 mpg in the mountains and 8 to 8.5 mpg on flat land here in Colorado.
This was towing a dolly with a Ford Escort on it. I will now be towing a 2001 Jeep Grand Cherokee on all 4 wheels {5200 lbs}.
My speed was at 70 MPH, tried 55 to 60 MPH and mileage went down.
Does anyone have any ideas?
We are planning a 6000 to7000 mile trip this year.
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Old 05-23-2022, 05:05 AM   #2
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Well, to start the Jeep does not weigh 5200lbs, more likely 4500.
Not sure how you were getting 8mpg at 70 mph? My 12 with the 5 speed towing my Explorer gets 7 at best!
I think you may need to rerun your numbers! Even my 02 V-10 Excursion towing a 35ft TT would only do 7!
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Old 05-23-2022, 05:10 AM   #3
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I drive 62 mph on mostly-flat terrain, tow an under-3000-pound vehicle four-down, and do well to get mpg better than 7.5. Typical mpg is 7.

I believe your coach has a four-speed transmission. Mine has the five-speed.

I am surprised that your coach's mileage decreased when you slowed down. I would expect an improvement of 20 percent or so when slowing from 70 to 55 mph.

I'm sorry to say that I can't offer any help, just commiseration.
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Old 05-23-2022, 07:26 AM   #4
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Something doesn't sound right. I have never heard of a box shaped vehicle getting better mileage at 70 mph than at 55-60 mph.
Of the seven motorhomes I have owned in 25 years, all of them had improved economy when driving 60 vs 70. Sorry, I don't know how to respond.
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Old 05-23-2022, 07:46 AM   #5
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One can drive so fast that to battle air resistance more downshifting occurs.
One can drive too slow and downshifting occurs due to loss of torque. Most vehicles have a torque range suitable for traveling approximately 60 MPH. Your results may differ as you try to find the point at which high gear predominates.
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Old 05-23-2022, 08:02 AM   #6
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IF the Jeep weighs more than 4000 pounds you MAY be exceeding the GCVWR of your chassis, depending on how much your coach alone weighs.
IF your MPG calculations are based on computing them on a single refill, that explains why you seem to have better than most ďaverages ď. Unless you calculate the average over several fillings and at least 1,000 miles it isnít a realistic average.

Not trying to seem critical, just trying to offer my thinking on both subjects. Ed
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Old 05-23-2022, 08:15 AM   #7
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Generally, the best way to improve mileage is to check weight vs. tire pressure, make sure the air filter is clean, find the optimal power rpm for your motor and plan on going slowly up hills by downshifting to keep the motor near the ideal rpm.

Start slow, leave plenty of room to coast towards a gentle stop and enjoy the scenery.

We get (nearly) 8 mpg on a good day when fully loaded and towing our Jeep Cherokee. We drive at 63 with occasional excursions to 70 if downhill and little traffic. We get to drive in the slow lane going up mountains...
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Old 05-23-2022, 08:57 AM   #8
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Yeah something doesn't sound right. Slower speeds should generally yield better MPG. Details matter too. Were you always using regular gas? Was there hills, wind on the tank with the lower MPG?
I track all gas mileage since I went full time in 2017:
Miles MPG
6263 6.4 2021
20899 6.3 Since FT in 2017

I am right at 22,000 lb GVWR and tow a Ford Focus at 3200 lbs. generally driving at 62MPH. I notice the biggest variance when I have a head wind or a cross wind. It can lower that by 2 MPG easily.
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Old 05-23-2022, 09:05 AM   #9
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Couple of things to help improve mileage.

1. Reduce coach and tow weight. Each spring I empty the coach and anything I can't recall using the prior year doesn't go back in. I usually only travel with maybe 5-10 gallons of potable water and empty waste tanks. Every little bit helps.

2. Keep the tire inflated to the maximum necessary for the weight of the coach OR to the pressures listed on the Ford Incomplete Vehicle Tag. Ford's pressures will give your tires the weight capacity to match the axle capacity.

3. Leave the toad at home unless you have definite plans to use it. I rarely take the toad along for weekend trips but longer trips with site seeing plans I bring it along for the ride.

4. SLOW DOWN. 2500 RPM should have you running down the road at 62-65 which is a good safe, fuel and time efficient speed. I can't recall the formula for air resistance changes with speed but it's substantial and the 100+ SqFt of frontal area of the brick we call a class A doesn't help much.

A good tool to help with your right foot is a Scan Gauge which you can set up to display both average and instant fuel mileage as determined by the ECU. Seeing an instant number of 2.2 MPG has a way of getting you to back off a bit.

If your speed reduction and mileage decrease was based on a single fill up you really need several to establish a true average number. Only takes a few gallons more or less as part of a fill up to give you a mile for two of change in the calculated MPG which is easy to do when filling a 70 gallon tank. A strong head wind, a few miles of stop and go traffic, generator usage,,, will effect the calculation. I have over 187 fill ups and my MPG has varies from a low of 4.7 (my one and only time to experience a summer Friday evening Washington DC traffic) to a high of 8.74 with my average holding around 7.2.
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Old 05-23-2022, 09:59 AM   #10
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This is info from the Cat RV Performance Guide. It reflects my actual experience when checking mileage at different speeds.

A 34,000# motorhome will need 126 hp to overcome rolling resistance and wind resistance. That same coach will need 153 hp to travel 65 mph. Push it up to 70 mph and it will need 184 hp.

Every horsepower needs fuel. The higher the HP requirement, the higher the fuel consumption.

Edit: 70 is 16% faster than 60 so more miles are covered. However, 184 is 46% higher HP needed to do it.

Some might find this info useful.

https://www.prevostcommunity.com/PDF...%20economy.pdf
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Old 05-23-2022, 05:36 PM   #11
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Well, I rechecked the weight of the Jeep. On the door it says 5500 lbs. Figure that I fill the gas tank, put my mobility Scooter in the back, add in the braking system, and the Blue Ox Towing Bar, that sounds like the weight is close.
The mileage was on two long trips. One from Denver to Niagra Falls, and the other to New Orleans. Both took 6 weeks.
I always start up slow from lights, try to stay away from heavy traffic ETC. I use the speed control on flat lands and not in the mountains.
RPM is around 2000 to 2200 and I use the overdrive.
I don't know if it has an after-market chip and don't know where to look for it either.
I have had it for 10 years
Before this we had a 32-foot Bounder with a 460-fuel injected with overdrive and a full Banks system. The best MPG was at 52 MPH. 2000 RPM and 12.5 MPG on flat land towing the Escort. I did get 15 once with a tail wind.
I have had motorhomes for over 30 years.
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Old 05-23-2022, 05:49 PM   #12
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My tires are Iron Man they have a higher rating then Goodyear or ETC. 15 to 20 %. They last longer also.
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Old 05-23-2022, 06:10 PM   #13
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I have also made a spare tire carrier for is a second spare tire that installs into the trailer hitch. Adds 2 feet to the hitch. It has a pully system to raise and lower the spare. Less than 30 Lbs. needed to operate.
I'm a Mechanical Engineer and a Master Welder. This helps.
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Old 05-23-2022, 08:42 PM   #14
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I suggest you minimize your tanks. Empty the gray & black before every trip. Only keep enough water for the day. Don't fill your fuel tank; only do 1/2.

There is a lot of weight on those fluids.
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