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Old 10-26-2010, 03:59 PM   #1
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525 cummins MPG

hello everybody
need to try and help our new friends out with a little fuel mpg issue
they are getting what seems to be excessively poor fuel mpg with there 43' monaco with a 525 cummins @ 55 miles per hour they are getting about 4 mpg and monaco said it should be much closer to ten

Question: PLEASE can someone tell us what should they be exspecting to get with a 50,000 pound coach
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Old 10-26-2010, 04:32 PM   #2
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My Monaco is the 400 ISL and I seldom get "close to ten", more like 7.6 average. Of course, at 55 mph it might be better. My coach at 42 feet is a lot less than 50,000 lbs.

I met a guy at a rally recently who had a late model Monaco Executive with a 650 HP Cummins. He said he was averaging about 6. So 4 does seem low for a 525.
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Old 10-26-2010, 04:48 PM   #3
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Suggest he take it to a Cummins Service Center and have them look at the ECM programming, it may need tweaking.
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Old 10-26-2010, 04:52 PM   #4
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4 is low. 10 is..........................optimistic at best.
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Old 10-26-2010, 05:42 PM   #5
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If I drive my Monaco Signature at 55 MPH it is in 5th gear vice 6th gear. You need to check that. The other thing is that I believe that 55 mph is too slow for that ISM 525 HP motor. You are below the sweet spot and the torque curve. I have the Detroit Series 60 and my sweet spot for MPG is at 1450 RPM which is 62 mph and this gives me between 6.8 and 7 mpg. The motor just went over 30,000 miles and is not broken in yet. I bet you your MPG will improve if you speed up to 62 mph. Try it. A friend of mine get 6.9 mpg with his ISM with a 45' MH.
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Old 10-27-2010, 07:17 PM   #6
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MPG

We've had two different 42' Monacos with M11 450hp Cummins and both got between 8-10 mpg @ 60 mph, but they both weighed less than 40k Lbs.
Don
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Old 10-27-2010, 09:52 PM   #7
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I have a 42' with C12 which is fairly close to your friends. I get in the range of 7-8mph. IMHO 10 for them would be downhill with a tailwind. 4 would be uphill with a headwind.
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Old 12-23-2010, 02:26 AM   #8
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My average has been 8.9 towing the HHR......Dennis
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Old 12-23-2010, 07:53 AM   #9
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Dennis, what speed do you normally drive at and what year is your MH? Thanks
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Old 12-23-2010, 12:57 PM   #10
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Cummins web site has.
Light Duty 6.5 mpg,
Normal Duty 5.5-6.5 mpg,
Severe Duty 5.5 mpg
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Old 12-23-2010, 01:12 PM   #11
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Ten MPG is waaaaay optimistic. Most of the guys we run with get about 6-7.5 that have either the Series 60 Detroit or the Cummins ISM. I have the smallest engine of the group with the ISL and I get about 7.25 MPG when towing the trailer weighing just over 45k lbs. I am not easy on the go pedal either. I generally set the cruise around 68 MPH. Mike.
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Old 12-23-2010, 03:28 PM   #12
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On my last trip with my 40K+ lb MH with the Detroit Series 60 I was running an an absolutely flat road with one of those unusual zero wind days. Not a flag wavering anywhere. With these conditions I did some testing using my Aladdin readout and running for 40 miles for each test. Now remember no stop or starting or accelarating just flat road and constant speed. At 55 mph I had an absolutly solid 8.0 mpg and for every 1 mph increase I lost 0.1 mpg so at 60 mph I was getting 7.5 mpg and at 65 mph I was getting 7.0 mpg. It was pretty linear up to 65 mph and very consistant. Now no argument that my Aladdin may be a little off but it would have been off evenly across the test. Gave me a pretty good idea what speed was doing to me. Those zero wind days seem to be pretty uncommon and when there is wind it alsways seems to be a head wind (lol). On my next trip I am going to try and see how accurate my Aladdin is but that is pretty hard because I don't seem to be able to always fill my tank to the some point each time. I guess the trick is to first level it at the pump then try and fill it to the brim of the filler neck. I would think the ISM 500 would be pretty close to the same MPG in the same weight MH.
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Old 12-24-2010, 11:00 PM   #13
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Really?
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Old 12-25-2010, 07:32 PM   #14
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One thing that can cause low mpg is the turbo boost is not working because there is a leak the system. I had a leaking exhaust manifold when fixed my milage went from below 6 to over 7. Once the clamp for the air charge cooler came loose and lost tons of power and fuel economy. Bill 2000 american eagle rv
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