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MPG

Reply #25 –
Yahoo Message Number: 26000
I have the 400 ISL engine-

Question- Is there a sweet spot for RPM that gives the best MPG? I don't have Silerleaf- would Silverleaf tell me that?
Also I've never change the air filter in engine- I'm the original owner with 50,000 miles- I've done the reset on the filter gauge- It pull's up the yellow tab in the clear cyclinder slightly- Also pulled the

hose off and checked for suction- with engine running- Suction seemed good-

Thanks for any help-

Stan vander ploeg
#11556 Intrigue 2003

Re: MPG

Reply #26 –
Yahoo Message Number: 26001
As slow as it may seem, we found that 55 gave us the best MPG. We have the 400 ISL as well.

Sue

Allure 31254

Re: MPG

Reply #27 –
Yahoo Message Number: 26002
We discovered the same, that 55 MPH is the sweet spot for us too.
55 to 65 the MPG goes down from about 9 to 7.
Driving at 55 also has another good side..
It is much more relaxing. It helps us just sit back and enjoy the trip.

Russ and Jean
05 Intrigue
11883

Re: MPG

Reply #28 –
Yahoo Message Number: 26004
The majority of Cummins ISL engines operate best "around" 1600 rpm - most rigs are geared to run at 55 mph at 1600 rpm. Peak torgue on your engine is at 1250 rpm so that gives you a good operating range between shifts. A number of tests were run within the trucking industry that suggest that your miles per gallon will decrease 1/10 of a mpg for each mph over 55 you drive ie. if you drive 65 mph avg. you will see approx. 1 mile per gallon less in overall mpg. These test were run back in the early 1980's and I have not heard of any tests run since that time that indicate anything different.

Naturally a number of things have an impact on your overall performance including how you drive, idle time, dirty air filter, oil change intervals, type of oil used, tires and tire pressure along with weight of the coach and if you are towing anything behind you. I would change your air filter ASAP if it is org. equipment with 50,000 miles on it regardless of the filter minder reading. It is not that expensive to replace and is far cheaper than an engine overhaul. Dirt is your engines biggest enemy. New, clean air, oil and fuel filters are your engines best friends!!

I have the ISL 370 hp which is in the same family of engine (different turbo) - I get my best mpg at 55 (as high as 9.1 mpg) but I find I generally drive around 58 to 60 and normally will see 8.3 to 8.7 mpg. Since we dry camp alot we use the generator regularly (and the Hurricane Heater) both of these bring my overall avg. mpg down. I believe 7.5 to 7.9 overall would be a fair number tp expect if you use your generator and heater on a regular basis.

My Silverleaf shows rolling mpg but does not show overall trip mpg.

Hope some of this helps you.

M. Peterson

03 Allure #30916

Quote from: stanley20002152
I have the 400 ISL engine-

Question- Is there a sweet spot for RPM that gives the best MPG? I > don't have Silerleaf- would Silverleaf tell me that? >

Also I've never change the air filter in engine- I'm the original

owner

Quote
with 50,000 miles- I've done the reset on the filter gauge- It

pull's

Quote
up the yellow tab in the clear cyclinder slightly- Also pulled > the

hose off and checked for suction- with engine running- Suction

seemed

Re: MPG

Reply #29 –
Yahoo Message Number: 26006
There is a interesting tech. report published by CAT. but applicable to all engines relative RPM (speed) and fuel economy, as related to aerodynamics of most coaches. Everyone is right 55-60 speed for greatest mileage. See CAT. for report.

Re: MPG

Reply #30 –
Yahoo Message Number: 26017
AT home comming during a Cummins seminar we were told you must change the filters when dirty or every two years. The adhesive that holds the filterpleats in place will fail and if it does and (the filter is dated) the repairs will be all yours. And I understand that can be a very very expensive proposition when all that gunk gets in the turbo and in into the cylinder heads. TWI 11731 2004 Intrigue w2ith ISL

Re: MPG

Reply #32 –
Yahoo Message Number: 26031
Mike,

Interesting paper that's a keeper. It will be worth reading.

Thanks,

Jim Hughes

2000 Allure #30511

Quote from: Mike Cebula\[br\
]
Cummins has a white paper on MPG. It is aimed primarily at the
trucking industry, but has good info in it. I learn a bit more
each time I go through it.
http://www.cummins.com/na/pdf/en/products/truck/MPG_Secrets_Whitepape .pdf

Quote
Mike

'95 Magna 5266

James Spivey wrote:
>
>

> There is a interesting tech. report published by CAT. but
applicable to
 

Re: MPG

Reply #33 –
Yahoo Message Number: 26039
50,000 miles on the original air filter. You must be kidding. That engine has to be in labor just to keep running. If you have black soot every time you accelerate your starving for fresh air.
I've read your message 3 times just to be sure.
You don't even know if you have an air filter in the filter can. Maybe that's why its still running.
Absolutely shocked in KC
AL

00 affinity #5851