Diesel fuel mileage and additives

[sleprr]

I bought a new 2008 Allegro Bay 37QDB, Freightliner chassis, Cummins ISB 6.7L. 6speed Allison Tranny in March of 2009. The first 1000 miles pulling a 4200 lb jeep, at 62mph average, 100psi in the tire, average load, I averaged 8.7 mpg. Driving in the Rocky mountains with 4200 miles on it I was not overly impressed with the power. This is my first diesel and I have read a lot of discussions and ads on fuel additives to clean up the diesel fuel, lubricate the injectors, prevent freeze up, boost cetane, etc. Has anyone had any experience in performance or mileage improvement using additives? Will my performance improve as my engine gets broken in? Should I change out the primary and/or WIF filters, thinking they may be clogged from sitting on a dealers lot for a lengthly period, thus resulting in poor mileage? Thanks.

[wagon217]

I don't think that is bad fuel mileage at all for the miles you have on the engine. I would NOT use additives to your fuel as if you do a bit of researching on the Cummings site I think you will find that they recommend NOT using additives. My recommendation, filler up and enjoy the trip.

[LargCarPilot]

I have owned/operated diesels for 30+ years in the transportation industry. I have probably (at one time or another) tried every product available on the market. I.E. Howe's, Lucas, etc. I have been using a product from Scheaffer's for the last 7 years and had a significant reduction in injector and fuel system problems. I am currently operating a large bore Caterpillar out putting over 900 horsepower to the rear wheels. Fuel system operation ranks high on my list of priorities!

Schaeffer Oil | Diesel Fuel Additives, Conditioners, Treatments

[Elkhartjim]

8.7 is darn good IMHO. Cummins recommends you not use any additives.

[sleprr]

My owners manual says do not use additives in the oil and says nothing about fuel additives. Cummins has a site which identifies several additives and their advantages according to Cummins. The site is cummins fuel additives

[Gary RVRoamer]

The ISB is not a large engine for that size coach, so it is not surprising it does not impress you with its power. An ISC or even an ISL would be more appropriate to that size/weight, but would have upped the price quite a bit. Owners with somewhat smaller rigs and that engine are seeing 10+ mpg consistently.

If you find a fuel additive that somehow manages to increase the energy per gallon of diesel, the world will beat a path to your door and you will be a wealthy man. Good luck in your search!

[PizzaGuy]

If I got 8.7 I would have a party. My ISL 400 gets just under 8.

[Eddie Foy]

Shoulda bought a Mercedes. My 07 Presidio 39D with MBE 926 gets 10.5.

[Elkhartjim]

Quote:

Originally Posted by Elkhartjim 8.7 is darn good IMHO. Cummins recommends you not use any additives.

My bad. The whole time I'm reading this I'm thinking oil.

[Korryp]

My local Cat dealer who does only work and no sales of fuel additives mentioned that he has seen fewer problems with rigs that use Stanadyne in every other fuel fill up.

[Mahof55]

I have a 1993 pusher 32 ft 5.9 slightly overloaded mechanical Cummins and the lowest mileage I have clocked was 8.5, with a fuel leak in the bottom of the tank, since repaired. I also drop to about 15 mph climbing all mountains, which is ok since all the Big trucks are right with me.
It is true that in the beginning of an engines life its efficiency is less while it is breaking in, after break-in it should improve slightly but do not expect a huge difference. The power and torque on a 6.7 B is similar to my 5.9, increases were required to get around emission laws. You have the added issue of that coach being a front engine diesel (I think) instead of a pusher, if so it has and will continue to have all the issues that a A gas coach has.
Get through the warranty period and look at a Banks kit.

[Cruzer]

A 37QDB Allegro Bay is at the heavier end of the FRED chassis applications. You won't be getting the same fuel economy as an Allegro 34TGA for instance. But, there are a ton of factors that come into play also. For one, the unit is new. It takes time for any diesel engine to break in before it will get to it's normal fuel economy numbers. My ISL gradually improved up to 30,000 miles but it tapered off quite a bit at 15,000 miles. Also, you checked it climbing the Rocky Mountains pulling a fairly heavy toad. We do this all the time and it makes a big difference. Your coach probably spent as much time climbing vertically as you did going forward . Of course speed is always the biggest killer of fuel economy. Every 10 MPH that you gain probably costs 1 MPG because the wind drag increases exponentially as the speed increases and it take more horsepower just to move that big brick down the road. I'd give it a bit, then try it on level roads after a few more miles and see what you get. It will improve but I doubt that you will ever see the 11+ MPG that some of the lighter FREDs see.

As to fuel additives I find that I gain very little with them. Fuel additives serve to augment deficiencies in the fuel. If your fuel is decent in the first place you should (in theory at least) not need anything. If your fuel is lacking, old (stale), or you have some adverse conditions (high fuel tank condensation, extreme cold temps, etc) you may find value in them. I've used them in the past but not found any benefit to them in my case. In fact, I've now stopped using them upon the advice of AquaHot. I did have issues with my HydroHot hydronic heating system burner and AquaHot advised me that fuel additives can mess up the burner and take out the nozzle. Naturally, this isn't an issue on an Allegro Bay but I do have to wonder if any of these addditives might affect the emmissions gear, such as the DPF (Diesel Particulate Filter) in a negative way.

[ljr869]

Get your fuel at truck stops, not the normal stations that happen to sell diesel (it sits too long). Keep your filters clean. And another vote for Stanadyne. (I have a F-350)

[Triker56]

Slowing down will gain you MPG.
34' ISB 5.9L 55-58 MPH towing a HHR this summer so far average is 10.991 MPG

I use Summer Opti-Lube http://opti-lube.com/