BAC Forum
General Boards => General Discussion => Topic started by: Keith Moffett on October 08, 2017, 09:13:40 AM
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We just filled up the tank with diesel. The interesting thing is that it took only 16.3 gallons. I literaly tried to squeeze a bit more in but no way. We had traveled 164 miles from full to fill up. By my math that says just a tad over 10 mpg. In light traffic on state highways and hilly country.
I would love to figure out what we did right so I can do it again. Lol
Got to appreciate the good days!
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I was surprised similarly once after a 600 mile jaunt, and calculated 10mpg. It was all freeway, and cruise set at 60 to keep it from slipping down to 5th gear. But on reflection and weather check, I realized the wind was at our back virtually the entire way. I've since been more attuned to wind direction on trips, and conclude it has more effect on mileage than most of us think. On subsequent drives along the same route I've not posted such good numbers; there were more head-on and side winds.
Joel
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Keith it must have been down hill, in 9 year with our C13 I would see brief times of 8mpg but when I check the trip log on the Aladdin it's always 6 bummer
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Wind can raise havoc with fuel consumption. Yesterday I only averaged about 6-7 in my Jeep Liberty towing a small trailer and fighting a strong headwind all day.
Steve
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Gentleman, fuel milage ( what is that ) ?? Your engine ECM holds that information along
with engine rpm and miles. In most cases milage Cat 3126 to C-9, 7 - 8 mpg. Cat C-12
10 mpg, Cat C-13 - C-15 5 - 7 mpg. This is information extracted from engine ECM for
many members with Cat ET computer readout and printout. The Cat C-12 hold constant
10 mpg. There are many areas will reduce milage, wind, speed, load, tire size etc.
Dave Atherton Retired Cat Mechanic
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Keith,
There is a factor that you probably did not consider, how level was the coach from side to side when filling on the last two fuel stops. With the fuel tank location on your coach (side to side), you can use the leveling system to raise one side of the coach and add as much as another 20 gallons to a previously full tank. Therefore, if the coach was not identically positioned, your short distance test was meaningless.
To test fuel economy by the amount of fuel pumped, you need to test several tanks of fuel with the coach perfectly leveled at fueling, and accurately track the amount of fuel used by the Onan and AquaHot. The most accurate fuel mileage that is available to anyone that does not obsessively track consumption in this manner is available by reading mileage from your Aladdin/Silverleaf system. Anything else has too many variables that make an accurate or even a close calculation impossible.
Gerald
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We get about 5 mpg and that includes usage through the generator and AquaHot. I keep a log of location, miles driven, gallons to fill, and fuel cost per gallon at every fill-up. The lowest I have seen in five years was 3.8 mpg, the highest was 6.3 mpg. I do not keep track of the hours of usage by either the generator or AquaHot between fill-ups. Downhill makes a huge difference, obviously. And traveling at 62 mph instead of 68 mph seems to make a substantial difference as well.
I usually try to tilt the coach away from the fuel pump when I fill the tank. That seems to help not only the fuel flow down the tube into the tank, but also helps get the tank filled closer to full.
My brother has a 2000 Beaver Marquis Tourmaline with the C-12, 425 hp engine. He gets 8-ish or better mpg and tows his pickup.
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My Aladdin Jr gives fuel used by engine so my assumption is that it should be fairly accurate.
Steve
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Keith,
On "economy days" I would set the cruise to 55. The Alison would rest in fifth. With a tail wind on a flat interstate I would see as high as 11 when the 12 year average on the Cummins was 8.3.
Bill
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On my Contessa I see about 7.5 mpg continuously with the 3126B CAT. And thats towing my SRX. I don't really pay much attention as we used to have a large boat and cried at the pumps a few times.
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My similar ‘06 Marquis/C13 hasn’t hit 7mpg yet, even on straight level flat ground.
One interesting observation on the road this summer for the first time with the Marquis: Increasing my speed from 60 MPH to 65 MPH on cruise control did not result in any reduction in fuel consumption. I think that this is because the “Sweet Spot” for the C-13 is around 1650 rpm, and 65 mph puts me pretty close to that engine speed.
Just a couple of other observations:
For a 45’ coach weighing north of 50,000 lbs, full of liquids and Doritos, with a C13 Cat to average 10 mpg on relatively level ground, under almost any conditions is almost impossible. This raises the probability that some undiscovered variable was in operation. I have gotten wildly varying figures when I thought I had filled the tank, but failed to notice that the coach was leaning toward the fill spout, for instance.
My Alladin system is consistently inconsistent in its read outs, for another. It is currently showing a 5-7% lower odometer reading (compared to my GPS).
Also as previously mentioned, a strong tailwind can also provide surprising increases in mpg figures.
My previous coach was a 40’ MONACO Windsor with a 370 horse Cummins. It was more than 10,000 lbs lighter than the Marquis. Without a tow car attached, I could achieve a consistent 10mpg.
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Good points all. I have had the experience were we were on a slanted pad while filling. This was not the case in this instance nor was there a good tail wind. I did fail to mention that there was a moderate amount of time at idle for repairs etc. At no time were we in economy mode on the shifter. Perhaps I am dreaming but it is a nice dream just the same. Lol
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Bob, although some have modified their tranny's factory programming, it's common for the Allison to shift up to 6th at about 62 or 63mph. It'll stay there until the speed falls to 57. So at 60 you were likely in 5th, and in 6th at 65. The higher speed would have used more fuel had it stayed in 5th, so the cruise in 6th at lower rpm probably compensated, providing comparable mileage.
Where possible, my practice on open highway is to speed up into 6th, then let it slide back to 59-60mph, maintain that, and try not to let it slip on a slight incline back toward the 57 mph downshift. The cruise control is steadier than my foot also.
Joel
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That’s exactly what I do. Joel. I make sure I’m in sixth and then set the cruise. The Vorad out votes me sometimes if I tuck in behind a slow truck.
In California, I can’t go 65 in many places, and even though I’m actually more relaxed at 60, its nice to be able to step it up a little without worrying about burning extra fuel when happy hour is calling and you still have a ways to go.🍷🍷🍷
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Gentleman, fuel milage ( what is that ) ?? Your engine ECM holds that information along
with engine rpm and miles. In most cases milage Cat 3126 to C-9, 7 - 8 mpg. Cat C-12
10 mpg, Cat C-13 - C-15 5 - 7 mpg. This is information extracted from engine ECM for
many members with Cat ET computer readout and printout. The Cat C-12 hold constant
10 mpg. There are many areas will reduce milage, wind, speed, load, tire size etc.
Dave Atherton Retired Cat Mechanic
Is this right.... C-12 gets 10 MPG? Also will an additive make a difference?
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Fred, the ECM on Caterpillar engines reads out, fuel used engine idle hours, fuel used engine
running down the road gallons per hour, engine speed in rpm’s, engine fuel mpg. Note: the
engine reads only fuel used in engine not gen set or house heating. The information is pulled
from the ECM by using Caterpillar service tool called Cat ET and can be printed out. This has
preformed for many member by Dave at rally’s and many members have a copy of this. What
Dave posted earlier is information pulled from many motor homes. To answer your C-12 question,
the C-12 holds in most motorhomes 10 mpg. Again there are many areas fuel mileage can be
affected as stated by many. There are many add on information programs like the silver leaf
that also reads fuel mileage that may differ with Caterpillar OEM equipment but all information,
that is stored on Cat ECM is used for diagnostic information related to repairs and troubleshooting,
and only can be pulled from the ECM by Service tool called Cat ET of which Dave has.
Dave Atherton Retired Cat Mechanic
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Fred, the ECM on Caterpillar engines reads out, fuel used engine idle hours, fuel used engine
running down the road gallons per hour, engine speed in rpm’s, engine fuel mpg. Note: the
engine reads only fuel used in engine not gen set or house heating. The information is pulled
from the ECM by using Caterpillar service tool called Cat ET and can be printed out. This has
preformed for many member by Dave at rally’s and many members have a copy of this. What
Dave posted earlier is information pulled from many motor homes. To answer your C-12 question,
the C-12 holds in most motorhomes 10 mpg. Again there are many areas fuel mileage can be
affected as stated by many. There are many add on information programs like the silver leaf
that also reads fuel mileage that may differ with Caterpillar OEM equipment but all information,
that is stored on Cat ECM is used for diagnostic information related to repairs and troubleshooting,
and only can be pulled from the ECM by Service tool called Cat ET of which Dave has.
Dave Atherton Retired Cat Mechanic
Thanks for the info. I am getting ready to put fuel into my coach for the first time. Was wondering if I should use a fuel additive.... like opti-lube. Is an additive recommended?
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Fred, Caterpillar does not recommend any fuel additive in all there engines such as injector
cleaners etc. They do approve Fuel anti-jell in diesel fuel tank in cold weather operations.
Dave Atherton Retired Cat Mechanic
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Fred,
The C12 is not loaded down with heavy emissions controls and runs at a considerably lower RPM than some other CAT engines. Both contribute to the MPG. My C12 gave about 8.5 mpg, running at 65 MPH. (Wish I had another one in my current coach).
Steve
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[/quote]
Is this right.... C-12 gets 10 MPG? Also will an additive make a difference?
[/quote
The consensus on this blog and others is that fuel additives are not recommended by most engine mfg, and generally do little or nothing to help modern diesel engines improve mileage or performance.
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Fred,
There are many variables that influence fuel economy, and even though the C 12 is a very fuel efficient engine, I do not think that you should expect a consistent 10 MPG. From my experience, your coach normally runs in the 8 to 9 MPG range.
I have driven two different C 12 equipped coaches towing Jeep Grand Cherokees over the last 13 years, a 38,000 plus pound 2000 Marquis (8 to 8.5 MPG) and a 50,000 plus pound 2002 Solitaire (7.5 to 8 MPG), and in about 180,000 miles, I have never seen a consistent MPG over 8.5 regardless of the speed. I have seen 10 MPG on trips with a consistent tail wind, especially if I was dropping in elevation, but I have seen 5 to 6 MPG with a head wind or when gaining in elevation.
Gerald
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My Aladdin monitor shows 5.5 mpg from 'born on' date (0 miles) to now. We bought our Patriot Thunder with 35000 miles on the odometer; we've put on about 10,000 mi over the last 3 summers, and the 5.5 mpg that the Aladdin reports seems to be pretty accurate, much to my dismay. 10 mpg on a C-12? Tell me it ain't so.....
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Gentleman, fuel milage information off Caterpillar ECM, many good post and many areas that
are different. I guess being a trained with Caterpillar electronic engines and service tool to
Retrieve information off ECM called Cat ET is Caterpillar Service tool, to this date Cat ET is used
daily. All information is stored on History section starting since key started engine for the first
time. Myself cannot dispute with fuel milage pulled off ECM, with computer information using
Caterpillar service tool ET. In Next note: Cummins engines use what is call InSite service tool
to retrieve same information that Caterpillar ET does and many members have copy of information
That Dave has made for them doing Diagnostic readout for problems and active fault codes.
Dave Atherton Retired Cat Mechanic
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Once again, lots of good info here. In following this fuel mileage thread, we have seen 3 different readouts on our rig & am not sure if different tire Mfg's have different dimensions or what may be the reason for our inconsistencies. Our Garmin GPS says 62mpg, speedometer says 59, Aladdin says 60-60.5. Can the ECM/speedometer be corrected to match the Garmin, as I believe it to be closest to actual?
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Dennis, I guess the last reporting Device is Caterpillar Service tool to readout all Caterpillar
ECM. One thing maybe several do not understand. The Caterpillar ECM is made strictly for
Caterpillar and the information on the ECM and other engine info. is bought from other companies
from Caterpillar and over the years certain values and information is held back from these
Aftermarket company's to maintain there edge on technical information for there own product
and service shops. There are several data connections to connect to ECM which mainly you
will find 6 pin J-1708 and 9 pin J-1939 to connect up your engine. Where problem comes into
play the software on aftermarket and Cat OEM not all the same along with fault codes. Again
service Cat ET is used in the electronic engine for many diagnostic problems and some areas
such a silverleaf and other brands Caterpillar will not give out much information but I do
know miles traveled, engine rpms, fuel used per Hour, miles per gallon can be bought up at
a caterpillar service shop as to what is on your Caterpillar ECM for a cost.
Dave Atherton Retired Cat Mechanic
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Just to add to the conversation. My 03 PT with C-12, Aladdin displays MGP since born is 7.2. 12K+ miles this summer from FL-Alaska and now in Albuquerque is 6.9MPG. I would sure love to see 10 MPG. Better than the 5.0 I expected when I bought the coach 3.5 years ago. until this summer I cruised at no more than 62. I have increased to 68 this year just because the coach seems to have a sweet spot at 68-70 where everything just gets smooth and easy!
Edit: I tow a 6500 LB PU truck everywhere!
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Hi Folks, I thought I would pitch in here. For the past 5 years we seem to average about 6.5 miles per gallon with our C13, pulling a 2011 Ford Edge, and we are almost always driving through mountains. We tend to drive the speed limit. I think the mileage is reasonable for the weight and aerodynamics (not).
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Had another Senior Moment & miss-typed the readings in earlier question. Should be MPH not MPG. Am trying to get consistency between the 3 different readouts I am getting. I can only guess that MPH are based on rear end ratio, tire size, & engine RPM for the speedometer & Aladdin readouts. Not too worried about gas mileage with this rig.
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Cat once published a book called "Understanding Coach/RV Performance". I no longer have a printed copy but I can email anyone a .pdf version. I'm not comfortable posting my email address on any forum, but it is in the membership book. Send me a note and I will return it with the .pdf attached. You might also be able to send me a "private" email on this forum.
Bill
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The CAT document "Understanding Coach/RV Performance" covering the contributing factors to fuel mileage is published in the Technical Library under Beaver Owners Manuals and in Common Problem under Poor Fuel Mileage. Thanks to Bill Sprague for making it available.
Steve
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Bill and Steve, thank you for bring out this information on Caterpillar fuel Milage this should
answer many questions. Dave Atherton Retired Cat Mechanic