MPG to expect

[Gary RV_Wizard]

Where's the fuel pump located for the generator?

Probably depends on the generator make and model. Since the generator is designed and installed separate from the chassis and fuel tank, I assume it will have its own fuel pump rather than in the tank, but it could be external (on the fuel line) or bolted to the genset itself.

 

[Lou Schneider]

Usually the generator is supplied as a package, complete with enclosure,etc.  The fuel pump is part of this package.  Look for a little square module in the fuel line.

 

[DonTom]

Usually the generator is supplied as a package, complete with enclosure,etc.   The fuel pump is part of this package.  Look for a little square module in the fuel line.

You mean the fuel line after it gets into the generator? I think I would have to take the generator out to find it. But it must be there, because I could not find it anywhere on the fuel lines under the RV. I checked a few days ago when I was last at my Reno home.  I will have to look at the generator manual again.

                                                                                     

-Don- SF, CA​

 

[mdbass]

I agree with the "never let it get below a 1/2 tank" rationale. Not championing for diesels; but I had one gas rig and that cured me-6.5 mpg tops! All my diesels have gotten 10-11 to the gallon. I understand the rationale for wanting to know mpg, but I also agree it's sorta mox nix after a while. I figure it costs me around $100-$125 a day to RV-and that's driving. (It probably got higher when diesel went to $4.00 a gal) We've been down this road many times before. Today its even more topical-have you checked the cost of hotels and eating out lately? Obviously, I love our coach, but I'm not trading for a hotel room anytime soon. Our opinion-go with a diesel with a slide. We fulltime now; but used one every other weekend or so for years and it worked just as well.

 

[Kevin]

10-11mpg WOW ;D

 

[maryland-david]

wll I have a pretty big Cummins and weigh around 50,000# with Toad and get between 6-7MPG. I thought that I would get better than that and I have a light foot.

 

[mdbass]

We dropped to 9.5 - 10 mpg last trip- 1300 miles with a toad. It can be done. BTW we are governed to 1850 rpm-(65 mph) and average somewhere in the mid 50 mph range according to our gps. We stay in the right (granny) lane and mosey along. The return in fuel savings more than justifies it. If you want to try this, make sure your mechanic adjusts the rail pressure when he governs the rpm. That way you don't lose your low end grunt.

 

[mdbass]

Maryland David-We have the small Cummins in a HR Endeavor. We also weigh a lot less than you. Geez-we're barely pushing 30,000 pds. Also; if you have a newer RV, it's probably controlled by several computers (like the DDEC system in Detroit engines). It really behooves you to use the cruise as much as possible if this applies to you as it is designed to maximize fuel consumption. You can also get a wealth of information from the computers (your mechanic can download it or you can purchase the adaptor to connect your PC or laptop to the onboard computer (via the PROM). Believe me, you won't be able to digest it all. It can help you with your fuel consumption.

 

[Kevin]

Not to start a fight, but how on earth do you not get run over on the interstate? you must be doing30 on the big hills too? I guess if that is what ya gotta do to get 9-11mpg then so be it,but I just can't run that slow :-\

 

[maryland-david]

Maryland David-We have the small Cummins in a HR Endeavor. We also weigh a lot less than you. Geez-we're barely pushing 30,000 pds. Also; if you have a newer RV, it's probably controlled by several computers (like the DDEC system in Detroit engines). It really behooves you to use the cruise as much as possible if this applies to you as it is designed to maximize fuel consumption. You can also get a wealth of information from the computers (your mechanic can download it or you can purchase the adaptor to connect your PC or laptop to the onboard computer (via the PROM). Believe me, you won't be able to digest it all. It can help you with your fuel consumption.

Yeah even with my extra 20,000#, I was expecting 7-9MPG. I have over 2 million miles driving big diesels and I have always gotten great fuel mileage. I just have not found a sweet spot for my combination. Of course I think that gap in the Allison 6 speed is too big. I ran 13 speeds and 18 speed transmissions most of the time. I am probably even dating myself but even drove a 6x4. At 65-70MPH I am near 6MPG. At 55-60MPH I am closer to 7MPG.

 

[Gary RV_Wizard]

I'm in between you two. We run at 32,700 lbs plus a 5000 lb toad for a total of 37,700 on a Cummins ISL 370. Cruising steadily at 63-64 mph (about 1650 RPMs) on an Interstate, we get 8.1-8.4 mpg. But if I try to do the same on a two lane road, the inevitable variations in speed due to traffic and towns put our average closer to 53 than 63 and the mpg drops to 7.2-7.6, no matter how light I try to keep my foot.

I find that I am not being run over at that speed, far from it. Some people pass me but others seem to be keeping around the same space. I even pass a few.

 

[taoshum]

Our last 3000 miles to Nashville and back averaged 8.9 MPG.  I set the CC at 65 on the big highways and about 60MPG on the smaller hiways. A headwind makes a large difference compared to a tailwind during the trip.  We were towing a Jeep wrangler, our weight was about 27,000 lb counting the Jeep and the engine is a small cummins diesel with a 5 spd Allision AT.  I try to keep the tank above the 1/4 level.  It was hot, so we ran the generator most of the time to run the house a/c.  I did vary the tire pressure (see the other thread) as experiments to improve the ride, plus we have a large elevation change to consider... 400 ft above MSL in Tennessee and 7800 ft elevation at home.  I really don't know what the MPG would be for a flat, smooth hiway with no wind, without a/c and a steady 60 MPH... maybe 9-10 mpg?

After a while, the only reason I even look at it is to detect a major leak or problem with the engine or drive train.

Very interesting thread.  Thanks.  Gary.

 

[BernieD]

David

At the last Cummins seminar I attended the presenter said that the "sweet spot" should be around 1650 RPM. I've tried keeping the coach in that area, 1625-1660, and my cruise is set at 62-63 mph. I've averaged tank fills of about 8.75-9.0 mpg and day figures of up to 10. A lot depends on wind, terrain and traffic.

 

[Marsha/CA]

Bernie, we are getting just about the same as you with a cat engine.  I knew about the "sweet spot" and it seems to work.  Tim keeps meticulous records on the coach...(well now that I think about it he keeps meticulous records on everything  ) and we seem to run fairly consistent.  However on that Gaspe' Peninsula drive we averaged 6.7 mpg something.  Those 14-15% grades really made a difference.

Marsha~

 

[maryland-david]

David

At the last Cummins seminar I attended the presenter said that the "sweet spot" should be around 1650 RPM. I've tried keeping the coach in that area, 1625-1660, and my cruise is set at 62-63 mph. I've averaged tank fills of about 8.75-9.0 mpg and day figures of up to 10. A lot depends on wind, terrain and traffic.

What size Cummins do you have? Do you have the Allison tranny? If so is this only 5th gear? I have not put many miles with an automatic transmission so I just let it pick its own gear. In my tractor trailers I always tried to keep the rpm at 1600, but due to the weight of 80,000# or so, it was also necessary for torque. However in 6th gear at 65MPH in my MH, I am way under 1600RPM. Maybe I'll try downshifting and see if that makes a difference.

 

[Gary RV_Wizard]

However in 6th gear at 65MPH in my MH, I am way under 1600RPM.

Way under??  You've probably got a larger, torquier engine than I do (an ISM or ISX?), but most Cummins configured for RVs are geared to hit 60 mpg as it shifts into 6th gear at about 1550-1600 rpms.

 

[BernieD]

David, I have the 400 ISL. IIRC at the seminar, there were some complaints from owners of the 500-600 hp engines about being able to keep the speed down and the RPMs up. Yes, keeping it in 5th gear was tossed out as an option. You'd have to play with it and see. Do you have an instant or rolling average mpg readout? That could help finding the sweetspot for your engine. That's what I had done and the seminar confirmed my results.

 

[Gary RV_Wizard]

Guys I know with late model American Heritages (your size of rig) are also seeing 6.x mpg.  2007 and newer engines are also running lower in mpg than those of 2003-2006, at least in the larger engines. Not so much difference at the smaller end (ISB & ISC).  Of course, every year the coaches got longer and heavier too!

 

[Kevin]

I find that I am not being run over at that speed, far from it. Some people pass me but others seem to be keeping around the same space. I even pass a few.

On our trip to florida and back I never passed anyone while going 65 or 70, I was passed by everyone but some of the poor ole governed truckers... oh well I seem to be getting 6-6.5 running the speed limit.

[edit]fixed broken quote[/edit]

 

[maryland-david]

Way under??   You've probably got a larger, torquier engine than I do (an ISM or ISX?), but most Cummins configured for RVs are geared to hit 60 mpg as it shifts into 6th gear at about 1550-1600 rpms.

Gary, I am going to have to check, but I am definitely at least 200-250 under 1650RPM. I understand with the bad fuel mileage of the 2007+, I believe this is due to the DPF. The regens on the DPF diesels do nothing but basically poor raw diesel into the exhaust. My 2008 Duramx diesel gets 2-4MPG less than a nopn DPF diesel. I have just assumed that the Allison tranny was smart enough to choose the right gear. I am going to switch into manual mode and see if my mileage increases from there.

Bernie, I do have the instant MPG gauge, even though I have never thought that they were very accurate, but it is a starting place nonetheless.

On this subject, has anyone noticed changing to synthetic oil in the engine making any noticeable difference in fuel mileage. I only have about 70,000 miles on my coach, so it is not too late to switch to synthetic.

Thanks,