Pedal Coach data from January 1st to June 30th


Have you ever noticed when you are getting gas for your car that you have choices? These choices are relative to the octane level of the fuel. What is octane and why is it more expensive? Ok, I know gasoline has nothing to do with a diesel engine but bear with me on this one.

Octane, a colorless flammable hydrocarbon of the alkane series, obtained in petroleum refining. Well, that didn’t tell us what I wanted but that’s what it is, let's try a different angle. The octane rating, the number on the gas pump of your options, tells you how much the gas can be compressed before it spontaneously ignites. The lower the octane the easier it will ignite without a spark, that is very bad. If you are running a performance engine it likely has a higher compression ratio and a low octane gas could damage the engine.

Now let’s talk about cetane. Cetane, a colorless liquid hydrocarbon of the alkane series, used as a solvent. Again, that’s what it is but maybe not what I wanted. Cetane is also measured by a number or rating. Both of these, octane and cetane, have much to do with the performance of the fuel you purchase. Cetane is the opposite of octane, the higher the cetane rating the easier it will spontaneously ignite, a good thing in a diesel engine.

A gasoline engine requires four things to make it run; fuel, air, compression and a spark. That’s why we want octane to be higher so it will only fire with a spark. A diesel engine only requires three things for it to run; fuel, air and compression. This is where the cetane comes to play. The higher the cetane rating the easier it will fire under compression.

With both octane and cetane, the higher the rating, to a point, the better chance the fuel will have a fuller, cleaner burn. This will lead to better performance and fuel economy for both types of engines. Is it possible to have too much in both cases? Maybe, I haven’t been able to find a maximum rating for either fuels but cetane is rated from zero to 100, 100 being the best.

I read an article where there is a diesel available in Northern California that has a cetane rating of 75 and the writer claimed amazing things using it in his Dodge/Cummins. I truly believe, no science to back me up, that it would be a great thing to have this diesel nationwide. It has been shown that the higher the cetane rating, from the refinery, the cleaner the emissions and the better the fuel economy, with a performance boost as a bonus.

There are fuel conditioners that claim to boost cetane ratings, they may very well do that but I believe there is a limit that you can improve the cetane rating with an additive.

The normal cetane rating for diesel in North America is in the 42-45 range with the minimum being 40, using the ATSM D945 as the standard. In Europe, the standard is EN 590 with a minimum cetane rating of 46 with premium diesel at a rating of 51 but can be as high as 60. There are 110 counties in Texas that must sell Texas Low Emission Diesel (TxLED) that has a cetane of 48 or greater. They do have the choice of selling an approved alternative formulation or comply with the designated alternative limits. The article I read doesn’t give specifics about what the alternatives are.

California has their own diesel fuel cetane minimum of 53. Premium types of diesel could have a higher cetane rating but may not depending on the supplier. Premium types of diesel often have additives that improve the cetane rating and lubricity along with detergents to clean injectors an minimize carbon deposits. They may also include water dispersants and/or anti-gel properties depending on seasonal conditions.

Looking at biodiesel derived from vegetable oil, cetane levels in the 46 to 52 range. Animal fat biodiesels in the cetane range of 56 to 60. If one were to just go by cetane levels, biodiesel would be a no-brainer. There are other issues that biodiesel brings to the tank, so we won’t even suggest that we go there.

How do you know the cetane rating of the diesel you are buying? That is a hard question to answer. You know the clerk at the fuel desk has no idea. If you really want to know, there are people at the corporate office of your fuel supplier that know people that know and could get you that information. Cetane isn’t a chemical that you can just pour in the tank. There are chemicals that will raise the cetane level but you need a chemist to tell you which ones and how much to add. I wouldn’t recommend this route.

The free market is a wonderful thing. Someone saw a need and made a product to fill that need, enter fuel additives with cetane boosters. I will seriously caution you about using these additives, too much can cause great amounts of damage and could void any warranty claims you may suffer. With that said, these additives can improve fuel economy and used properly will be cost beneficial. I would watch for extreme claims and walk away. Read the labels, read the ingredient list, go look up the chemicals to see what they do and any cautions associated with the said chemical.

Some engine manufacturers advise against the use of any fuel additives, others say use caution when choosing and using fuel additives, yet others have approved fuel additives. Check with your engine manufacturer if in doubt. Talk with others that use fuel additives, the internet is very useful but watch out for the keyboard cowboys. Read, read, and read some more, take out the extreme claims and the most critical offers and average the thoughts. For some, fuel additives will work, others there is no way to quantify that there was any improvement or change. It’s up to you to do the research and track your fuel mileage before and during the use of any fuel additive.

I just wanted to tell you the difference between octane and cetane for some background. I do wonder why the fuel retailers do not give us diesel buyers the option of improving our performance at the pump. An option for premium diesel with a higher cetane would be, in my opinion, used by those that know what it can do for them. Lower maintenance costs due to better, cleaner burning fuel can only be a good thing. Lower emissions, DPF cleanings extended, EGR valve problems reduced due to not returning as much soot thru the EGR and the possibility of fewer sensor failures can only save you in the long run even if the fuel was a bit higher in price.

There are some fuel stops that do offer #1 and #2 diesel but I have yet to see premium diesel offered. #1 diesel is typically a winter fuel because it will not gell as quickly as #2 but it has about 5% less energy than #2 diesel so you will get poorer fuel economy. #2 diesel has more properties that the refining process removes from #1 diesel that help with lubricity for the injectors, fuel pumps and seals. It also costs less to refine so it costs less at the pump. Until we get the fuel stops to give us the option of premium diesel we will just keep using #2 and if you feel the need, use fuel additives to get the most out of your fuel purchase.

Make good choices, be safe out there.

Comment (1)

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April 19, 2016



August 25, 2015


A very good and informative article. Great Reading and thank you!

July 20, 2018 9:43:25 AM