Diesel Pusher Question - RV-Dreams Community Forum

Trabuco · RV-Dreams Family Member

Diesel Pusher Question

Roz · RV-Dreams Family Member

When the terrain, road and weather conditions allow, our Cummins settles into about 1700 rpms at 64 mph. Yes, we are passed by others, but it is also a speed that allows us to enjoy our trip.

Occasionally, it is good to get out of this rpm, but we find the factors above do this for us and it is not necessary to purposefully make this change.

Bill Adams · RV-Dreams Family Member

You will find there really is not sweet spot. You travel at the speed you are most comfortable with and the engine will just keep you there. Most users report better mileage at slower speeds (55-62) but the difference in mileage may or may not make up for the additional time required to reach your destination or be appropriate for the roads that you are traveling.

NorCal Dan · RV-Dreams Family Member

Our transmission drops into 6th gear around 58-60 mph. I could override the computer, but I find 60-65 mph is a good speed that gives us economy with the fuel and where I feel comfortable driving. So far, from day 1, our coach is getting 9.9 mpg (based on miles driven and fuel quantity) and we are very happy with those numbers.

bjoyce · RV-Dreams Family Member

Bill Adams has it right since when we drive 55 we get better mpg than when we drive 65. I quit noting the rpms a while back since it did not seem to matter. We have a VMSpc unit that monitors our engine and displays the info on a netbook (or laptop). It is fairly accurate on fuel mileage and it does display the rpms. Yesterday we drove across eastern Oregon on US20 where the truck or towing speed is 55 and averaged 9.1mpg since it was mostly downhill. But the day before was mountain driving so we got 8.1mpg when we filled up. We have a 370 ISL and our overall mpg is about 7.3mpg. In most of the country we drive 62 to 65, so we are not getting as good of mpg as we could. I keep very good records in a spreadsheet and account for generator usage of 1/2 gallon per hour. My best mpg on a fillup was 8.78 driving east on I-94 across North Dakota. My worst mpg was 6.38 in the mountains of British Columbia coming back from Alaska.

Trabuco · RV-Dreams Family Member

NorCal Dan 9.9 sounds like outstanding mileage! The guy I bought my 2005 Monaco Diplomat from said he averaged about 7.5. But I think he drove a little faster then what you gys have mentioned. Somewhere around 70mph is the impression I got. I see us driving the rig around 60 +/- most of the time so maybe the mileage a little better.

Bill Joyce can you explin the VMSpc unit you mention above?

Thanks for the info!

Bill Adams · RV-Dreams Family Member

Take a look at this about the Silverleaf VMSpc software.
http://www.silverleafelectronics.com/?q=node/6

-- Edited by Bill Adams on Wednesday 5th of October 2011 11:07:50 AM

bjoyce · RV-Dreams Family Member

My friend Norm Payne (no relation to Howard, but they know each other) has a nice writeup on VMSpc to add to the link that Bill Adams put up - http://www.seeya-downtheroad.com/InformationPage/SilverleafMonitorVMSpc.html. I bought mine from http://www.rvupgradestore.com/SilverLeaf-VMSPC-p/vmspc.htm. You do need to determine if you have a 6-pin or 9-pin connector. I have a 9-pin with my 2004 Spartan/Cummins and a friend with a 2002 Freightliner/Cat has a 6-pin. I have the old serial port unit, but the new one uses USB. It does require a Windows PC but you can use a cheap used notebook and never put it on the Internet if you are a Mac or Linux user.

Trabuco · RV-Dreams Family Member

I really like the writeup Norm Payne did. In fact it's now on my list to purchase! Thanks Bill and Bill for the lead. You guys stayed tuned I'm sure I'll have more question as this is my first diesel pusher.