Diesel Fuel Quality and MPG

[gpascazio]

Up until this past weekend I did not believe that there was a difference between the diesel from different companies. This past weekend we to a trip to Silver Lake in Michigan. Silver Lake is a off roading State Park. I left Chicago with the camper and a half tank of diesel purchased from Citgo. The MPG by the time I filled up in Indiana was 11.4 MPG which is normal when I go from the unloaded truck to the truck with the camper. I filled up at Pilot we kept a steady speed of about 65 MPH. The MPGs kept going down until we got to Silver Lake where it was at 10.9 MPG. On our way back I filled up at BP near camp. Gas mileage started to go back up even though we were traveling at 70+ MPH. By the time we got home the MPGs were back up to 11.4 MPG. Since I always use a cetane booster I figured that the basic diesel fuel did not make a difference. I guess I was wrong. the truck seems to run much better on Citgo and BP. It is quieter and there is more power when I step on the gas. Has anybody else experienced this or did I miss something.

[NHIrish]

ah64id wrote:

jimh425 wrote:

ah64id wrote:
Cetane booster actually lowers the useable BTU's and thus economy. This has been proven on the dyno, and chemically.

References? It it is somewhat common knowledge that additives are a good thing especially with respect to adding lubricity.

Lubricity additives are good, and Cetane additives can be good as well when used at the appropriate time... but 99% of the time, or more, they don't do what people think they do.

My motor will actually sound horrible in the right conditions with Cetane boost, same conditions without it and it sounds normal. They are designed to run on the level of Cetane at the pump.

Cetane is really only good for helping the truck start, and improving the quality of combustion at low temp and low load.

I run Amsoil Diesel Concentrate, it does all the things I want without a Cetane increase.

As you can see here anytime Cetane is increased the BTU's decrease.

You are right about the fine print, but there is more to it...

http://farmweeknow.com/blogs-benefits-high-cetane-diesel-fuel-3681

[wintersun]

When I travel south I have the wind at my back. Returning and heading north I am driving into the wind. Difference of about 20% in MPG. If the wind is up over 15 MPH the difference can be as much as 30%. A truck with a cabover camper has the aerodynamics and drag coefficient of a brick.

[AH64ID]

jimh425 wrote:

ah64id wrote:
Cetane booster actually lowers the useable BTU's and thus economy. This has been proven on the dyno, and chemically.

References? It it is somewhat common knowledge that additives are a good thing especially with respect to adding lubricity.

Lubricity additives are good, and Cetane additives can be good as well when used at the appropriate time... but 99% of the time, or more, they don't do what people think they do.

My motor will actually sound horrible in the right conditions with Cetane boost, same conditions without it and it sounds normal. They are designed to run on the level of Cetane at the pump.

Cetane is really only good for helping the truck start, and improving the quality of combustion at low temp and low load.

I run Amsoil Diesel Concentrate, it does all the things I want without a Cetane increase.

As you can see here anytime Cetane is increased the BTU's decrease.

[jimh406]

ah64id wrote:
Cetane booster actually lowers the useable BTU's and thus economy. This has been proven on the dyno, and chemically.

References? It it is somewhat common knowledge that additives are a good thing especially with respect to adding lubricity.

[generaljean]

We notice a difference in diesel mileage traveling from Michigan to Florida in december and then again Florida back to Michigan in April. We figure most of it is due to temperature change and the diesel engine running better in warmer climate. Might be a factor for you?

[Raften]

Since biocides was mentioned, if your truck sits a lot and if you use a biodiesel blend, put some biocide in there. It might just save you a problem with filter clog.

[trail-explorer]

gpascazio wrote:
.... Gas mileage started to go back up.

you put gas in it?

[mlts22]

I can see two diesel additives: An anti-gel to use in the winter so the paraffin stays liquid. Then, a biocide, especially with biodiesel, to keep the bugs at bay. I read about cetane boosters and other stuff, but I've not really seen anything it helps with, but I could be wrong, but like posted above, it might be useful for long periods of idle time.

[AH64ID]

In 85K miles I have only ever had 1 tank if fuel that was subpar, 14 mpg empty and the next tank was 17. Both the same day on the interstate with similar weather. I'd never hit 14 empty prior, and haven't since.


Cetane booster actually lowers the useable BTU's and thus economy. This has been proven on the dyno, and chemically.

About the only time Cetane booster is good is when the tank will primarily be used in cold weather at low load. I use it for elk hunting and the like, where I won't get above 20 for a few hundred miles and many hours. Engines are designed, timed, around the cetane from the pump and that's perfect nearly all of the time.

I won't buy additives with cetane boost for this reason.

[drc5900]

In concurrence with the above posters for possible causes.

For me, a 0.5 MPG fluctuation isn't something I would get excited about.

When I travel many miles, I keep track on paper with actual numbers, and don't go by display in cab. If over many 1000's miles a negative difference would occur for a specific fuel brand, I would avoid that.

Did on all fill-ups a perfect top-off happen?

[SDcampowneroper]

refined fuel for many places comes from the same refinery. No difference in base fuel. Some retailers add lubricating or cetane boosters.
Improved mileage is in the density of the fuel, not additives. Summer #2 Diesel is heavier, denser than # 1 winter thinner fuel with its low gel point and easier low temp start .
This is the time of year for northern refiners and sellers to have some winter #1 blend fuel left in their tanks, transitioning to #2 summer diesel with its better power and mileage. Maybe you got some of that.

[Gonzo42]

Pay attention to whether you are getting all diesel or a blend of regular and biodiesel. Some folks have no problem with these but others do.

[BB_TX]

I would not put much in the differences in single tanks. Mileage can vary quite a bit on wind, elevation change, speed, traffic, type of terrain, temperature, etc. You would need to run multiple tanks of each fuel over time to know for sure.
But this are also differences in cetane ratings of various brands. Some, including Pilot, Flying J, Valero, and others have cetane ratings at the minimum of 40. Others have cetane ratings in the mid to upper 40s according to info posted here in the past.

[JumboJet]

I have heard talk of the difference in Winter blend and Summer blend.