My best MPG according to Silverleaf

[Richard Cooper]

Since I filled up with diesel at the Pilot just north of Medford, OR my Silverleaf says I am averaging exactly 9 MPG driving my C-12 over 2 days and now south of San Jose, CA.  I am real pleased with this as before I never got over about 8.4 MPG.

Met the expert on Aqua Hot systems while at 7 Feathers Beaver Rally last month and he said he was averaging 10-11 MPG on his older Patriot.  Don't know the details of his engine or weight, but he said he adds Hawes Diesel Fuel Additive and it increased his mileage significantly.  I've yet to try that.  I could have bought a gallon of it at the last truck stop, but didn't.  

What do you think or should I not bother with the Hawes additive?

[Edward Buker]

There is a lot of energy in diesel fuel. When you add a few ounces of an additive to a 100 gallons, that is a drop or two in dilution added to what goes into the cylinders at any time. It is hard for me to imagine that there is some miracle taking place where you get significantly more energy with those extra couple of droplets being involved. Just my opinion....

Later Ed

[Roy C Tyler]

I alwoys get about 9.8 MPG from Medford to Redding.  Once you get over the 7 or 8 miles of hill out of Ashland it is pretty much all down hill to Redding.  Now going from Redding to Medford is a different story.  I get closer to 7.5 MPG

[Jeff Watt]

7.5 mpg .... If I was able to get that, I must have won the lottery on engines. Now for  9.8mpg I'd need some form of divine intervention or allways down hill.

Chugging along at 5.8 - 6 mpg; gotta love the c13.

Jeff

[Keith Duner]

Slightly off target...  Years ago we had a Winnebago Suncruiser on a Workhorse chassis w/8.1 gas engine.  It had an Actia dash cluster that included MPG read out.  Best number seen was 58 MPG (downhill on I70 out of the Eisenhower Tunnel in the Rockies),  the worst was 1 MPG (uphill on I70 going into the Eisenhower Tunnel).

[Gary Winzenburger]

The best advise I got after purchasing our 1997 Marquis with a 3126 Cat is to keep the MPH around 60-62 and easy on the pedal. Our longest trip this summer averaged 12-14 MPG in central Illinois (flat as a pancake) to Missouri in the rolling Ozark hills. I use diesel additives on every other fill up, which was recommended by my local CAT dealer.

[Richard Cooper]

I had to climb mountains to have the downhill advantage, but used jake quite a lot.  I am not as confident with my rig as some of you.  I try to keep my speed less than 55 in them thar steep hills.  I could have had much better mileage had I just kept up with the truckers.

I mostly drove on the flats across Calif. about 58 mph.

Paso Robles today and weekend.

The most ever stress I had driving was yesterday coming down 680 near San Fran, Oakland, and San Jose.  Louisiana-like roads through San Jose.  I thought my windshield would crack any minute.  Hwy 101 is just as bad.

Good, good, good thing I got new Koni shocks put on fronts as I would have otherwise had bad issues driving this route to southern Pacific CA.  Most bounces I got were 2 little ones compared to 3 big ones earlier this year in other places.

[Gerald Farris]

Richard,
To answer your question about the advantages of a fuel additive when it comes to MPG, there are none. From the extensive research that I have done on the subject, you will save enough fuel with the use of a fuel additive to pay for the cost of the additive itself, and nothing more. I have read several scientific studies from engine manufactures, and they all came to the same conclusion. There are only so many BTUs of energy in a gallon of diesel and there is no way to instantly create more.

However, if you have microbial growth (algae)in your fuel or fuel with a low cetane rating (noncommercial US diesel fuel), the use of an additive to treat the specific condition would be beneficial.  

Gerald    

[Edward Buker]

Richard,

I average between 8.4 and 8.8 miles per gallon on our Marquis that is similar to yours. Headwinds, travel speed, and hills will cause most of the variations in mileage for any coach. Long term it has ben 8.6MPG. We travel at 60 to 64MPH and probably average 63MPH. The expected best MPG would be the speed at which you just hold 6th gear after the shift which would be about 57MPH to 58MPH. That is the lowest RPM in the highest gear with the least wind resistance penalty. That would not buy you much of an advantage over traveling at say 62MPH. These are heavy large coaches and it is amazing that they do as well as they do. We are lucky to have a C12 and an Allison 4000 for this job. Later years of coaches with emission standard limitations in engine design as well as bigger heavier footprints paid a penalty in mileage. On the plus side they are wonderful living spaces....

Later Ed

[Joel Ashley]

Well said, Ed.  Get into 6th and stay at the lowest speed that will not cause a shift.  I used to go 55-57 everywhere thinking it saved fuel, but realized I never was out of 5th gear there, and the coach wasn't a car.  That speed might have worked in our old 454 chev gas coach, but the Allison and diesel engine are different.  Nowdays I hit 63 to get into 6th then let it back off to 60;  57 may be the shift point, but get too close to it and she'll shift down at the slightest notion.  

Cruise control helps a lot where it can be used, as its electronics provide a steadier foot than humans do, esp. on long flat bumpy roads, eg. California.  And tail winds vs. headwinds play a larger part in fuel numbers than many realize.  

As to the Howe's product, Gerald is right - its best use is as an anti-gel when the coach is operated in or stored in cold weather.  Most diesel already has anti-gel in it, so the next best use for Howe's may only be anti-algae, and I use Power Service's BioKleen additive for that.

Joel