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07-02-2013, 07:54 PM
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#1
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Member
Texas Boomers Club
Join Date: Dec 2012
Location: Bacliff, Texas
Posts: 39
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Diesel mileage woes
I have a 40 ft. Safari Zanzibar powered by a 370 Cummins deisel. My last milage calc. was 4.7 mpg. What should I expect to get? What should I look at first?
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07-02-2013, 08:06 PM
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#2
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Senior Member
Winnebago Owners Club Fleetwood Owners Club Holiday Rambler Owners Club
Join Date: Dec 2011
Location: North East Florida
Posts: 1,994
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That's pretty poor. When I had a Cummins, I was getting 8.5 but one of my good friends only gets 5.5 in a 45' Beaver with a Cat motor
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2019 Horizon 42Q
Cummins L-9 450 HP
Maxum Chassis / IFS with Tag
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07-02-2013, 08:09 PM
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#3
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Senior Member
Join Date: Apr 2011
Posts: 2,569
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Air filter
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American Tradition 42R-Cadillac SRX Blue Ox Koni 5050XL MCD Scangauge D Samsung rf197
Fulltime since 2012
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07-02-2013, 08:13 PM
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#4
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Senior Member
Join Date: Mar 2013
Location: Fort Worth TX
Posts: 845
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I have the same motor in my 40' Dutch Star. My last check was 6.5 and that was after sitting and driving in a lot of traffic. I'm guessing 7.0 is probably closer.
As above, the first thing I'd check is the air filter. Then check to be sure you're not dragging an anchor.....
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2005 Newmar Dutch Star 4024
Pulling my 2012 Malibu w/Blue OX & Patriot brake unit
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07-02-2013, 08:22 PM
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#5
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Senior Member
Join Date: May 2012
Location: Deep in the Heart of Texas
Posts: 476
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Tal, how long have you had the coach? Any mileage calculation of less than 1000 miles is a little suspect. the level of the surface of the fueling station, fuel temp etc. can fool you. My last trip to eastern Al. & back had fillups showing 6.4 mpg to 10.2, Topped off tanks 10 mi. from home. Total miles to total fuel showed 8.2 mpg. Pulling toad & sporadic gen. use, I'm happy. Head winds, speed,hills, Interstate or back roads can all make a difference.
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2000 DSDP, 3883,Freightliner,330 Cat, 07 Jeep Commander 4x4toad.
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07-02-2013, 08:32 PM
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#6
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Senior Member
Join Date: May 2012
Posts: 3,816
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How fast do you drive?
What does you whole set up weigh?
What are your tire pressures?
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2011 MVP Tahoe 230 QB on Ford E350 Chassis
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07-02-2013, 08:44 PM
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#7
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Registered User
Monaco Owners Club
Join Date: Jan 2011
Posts: 949
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Huge Difference
Quote:
When I had a Cummins, I was getting 8.5 but one of my good friends only gets 5.5 in a 45' Beaver with a Cat motor
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There is a signficant difference between the 370 ISL and the Cat C13. The 370 drivers get about 7-8 mph, or about 140% of the C13 drivers' mileage. The C13 has 140% of the 370 ISL's horsepower.
Of course, many other factors affect mileage; but, both are solidly in the ballpark for their respective weights/hp ratings.
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07-02-2013, 11:05 PM
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#8
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Senior Member
Tiffin Owners Club
Join Date: Feb 2010
Posts: 331
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Our 40' Allegro, 330 Cummins-- I've been getting 6.2 mpg pulling our 26' Chaparral (around 7000 lbs), and high 7's towing air...
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2000 40' Tiffin Allegro Bus \ 2002 Regal 2860 Commodore
1988 53 x 14 Skipperliner \ 1995 32' Party Cruiser
1984 Goldwing Aspencade \ 1976 Harley Sportster
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07-02-2013, 11:30 PM
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#9
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Senior Member
Join Date: May 2004
Location: Auburn, CA, Havasu, AZ & Mulege, BCS
Posts: 5,385
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4.7 is way low. You probably have a leaking Charge Air Cooler so not getting the proper boost, and therefore improper fuel air mix; the Cummins will try to compensate w/call for more boost which robs hp, and more fuel which robs mileage. You can also drop 1mpg if you have a hydraulic fan stuck on high (not sure of your platform if you have that or rear radiator or some other config). Could also be a basic boost leak where some air tubing rubbed thru or a rubber connector blew.
You can test the CAC in the rig with soap solution but have to pull the tubing off & cap the intake & outputs the pressurize, or take it off the coach & do it in a tank dip style which is more positive. If you have the CAC w/the million small allen screws holding the end manifolds to the radiator section, your gaskets on the manifolds may be shot. A quick test drive w/Cummins software hooked up to the diagnostic port might show you are low on boost achieved vs boost commanded but that won't even show up till the problem is serious (the command feature can mask a certain amount of air leakage).
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Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project
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07-03-2013, 04:59 AM
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#10
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Senior Member
Join Date: May 2010
Location: N.E. Florida
Posts: 1,396
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Displacement?
Big difference in normal mileage for 8.3 liter ISC vs. ISB.
But nonetheless, your mileage indicates an air filter or CAC issue for sure.
DaveS
1998 American Eagle 40EVS
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07-03-2013, 05:50 AM
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#11
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Member
Gulf Streamers Club
Join Date: Jul 2011
Posts: 33
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just wondering what your average speed is when you were calculating your mpg
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07-03-2013, 05:53 AM
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#12
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Senior Member
Join Date: Nov 2008
Location: Cosby, Tn
Posts: 6,587
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Quote:
Originally Posted by talrogers
I have a 40 ft. Safari Zanzibar powered by a 370 Cummins deisel. My last milage calc. was 4.7 mpg. What should I expect to get? What should I look at first?
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Is this coach new to you? How many fill ups is this calculated over? Was anything out of the ordinary, like a lot of hills or stop & go traffic? Did you have a lot of generator run time?
You should have a filter minder in the engine compartment that will signal you to a dirty filter. Don't take it off to inspect or blow it out with air pressure. Diesels are unforgiving of any dirt getting into the intake air and air leaks in either the filter or the in take plumbing is very serious. A high pressure fuel leak will also cause a drop in mileage.
If this was just one tank then it's likely nothing. Don't get concerned until you have several fill ups over a couple of thousand miles to average out.
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Steve Ownby
Full time since 2007
2003 Monaco Signature
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07-03-2013, 08:17 AM
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#13
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Senior Member
Monaco Owners Club
Join Date: Jul 2011
Posts: 2,200
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Here's a question ..... were you running the generator? That can effect the mileage, sometimes cutting it in half.
When we traveled across the country last year we got 9.5 to 10.5 and that was towing a 20ft equipment trailer with a 4Runner and a fully dressed bike on it. Then we had to run the generator to keep volts up on the engine and our mileage dropped by half.
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Thom and Christine having fun in a 1993 Monaco Crown Royale Signature Series 40ft 300hp RV. Towing a Fiat 500 Abarth and a Harley.
Our blogged repairs and travels
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07-03-2013, 08:38 AM
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#14
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Senior Member
Country Coach Owners Club
Join Date: Jan 2006
Location: Northern California
Posts: 5,847
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Quote:
Originally Posted by PyrateSilly
Here's a question ..... were you running the generator? That can effect the mileage, sometimes cutting it in half.
Then we had to run the generator to keep volts up on the engine and our mileage dropped by half.
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Your generator could burn about 1/2 gallon per hour. If traveling 50 mph the generator should then reduce your mpg very marginally. Certainly not 5 mpg......
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Dean
1995 38' CC Magna #5280 **** Sold after 21 years of enjoyment.
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