Blue View – Do Cetane Boosters Really Work?

One of the many diesel additives

One of the many diesel additives

Note: Since publishing this blog, we received some helpful feedback from a good friend, which I have appended to the end.

There are a number of companies that sell “Cetane Boosters” - additives that are poured into the tank of a diesel-powered vehicle and which supposedly not only improve the MPG and power, but also clean and lubricate the injectors, remove water from the tank, make the exhaust sweet smelling, make your teeth whiter and your hemorrhoids shrink. Okay – I made up the last three, but you get the point. So, are these really worthwhile or just snake oil? The 6,000 mile road trip we just completed seemed like just the right opportunity to find out.

Cetane is a component of diesel fuel that makes it easier to ignite. The higher the cetane percentage, the quicker the fuel ignites in the cylinder, and the quicker the fuel ignites, the better the engine runs - up to a point. As with all good things, cetane should be used in moderation... as the cetane concentration increases, the diluted diesel cannot deliver as much energy, and power and efficiency begin to decrease. Having the right amount of cetane will enhance engine performance, while having either too much or too little will reduce it, affecting fuel economy and power.

You can determine how much cetane is in a given diesel fuel by its cetane number – the higher the number, the higher the cetane concentration. It costs money to add cetane to diesel fuel, and fuel companies, being in a competitive market, would like to save costs by adding less cetane.

Most modern diesel engines run best with diesel fuel having a cetane number of 48 to 50. Compare this with the U.S. required minimum cetane number for ultra low sulfur, highway diesel of 40, although the typical fuel runs between 42 and 45. Some regions in the country do have higher requirements, like California, which has a minimum cetane number of 53 for fuels sold in the state. In Europe, the current standard is a minimum cetane number of 51. You can buy better fuel - some premium diesels have a rating as high as 60.

When you drive to a gas station, the octane rating of the gasoline you are buying is posted right on the pump. Unfortunately, this isn't true for diesel. There is no way to ascertain the cetane rating for the diesel fuel you are buying, so unless you are in an area that requires a higher cetane rating or have found one of the rare stations that offer a premium diesel, you have no way of knowing what the cetane number is, and it's probably safe to assume the cetane rating is lower than what your engine would like.

To capitalize on this, there are a plethora of fuel additives available that purportedly increase the cetane level of the fuel. Before adding anything to the fuel, however, I checked the 8,000 page owner's manual for our Ford Transit to see whether there was any reason not to experiment with one of the cetane boosters – like voiding the warranty, for example. The manual did state that adding anything to the fuel that contained alcohol would, indeed, void the warranty, but it also stated that it was acceptable to add a cetane booster (presumably one not containing alcohol) to the tank if it was suspected that the fuel had a low cetane number. I'd say that was a pretty good assumption everywhere but California and Europe, neither of which was on our current itinerary.

I did a little research, and the most commonly used product was Diesel Kleen +Cetane Boost, a diesel additive made by Power Service. It's readily available from many sources, including most Walmarts. The plan was to drive a couple thousand miles using the cetane booster, then a couple thousand miles without, and the remainder of the trip using it again, then compare the fuel economy with and without the cetane. The majority of our trip was on 55-65 MPH county or state roads, with a few 70-80 MPH interstate highways and the occasional bit of city driving.

Per the directions, I needed to add 1 fluid ounce per every three gallons of fuel. It's a little tricky getting the additive into Blue's tank without making a mess, but I eventually came up with a method that gets most of it down his gullet without dribbling too much down his side.

A re-purposed catsup dispenser, marked in ounces

A re-purposed catsup dispenser, marked in ounces

A shortened plastic spatula to ...

A shortened plastic spatula to ...

to force open the filler tube

to force open the filler tube

The additive is stinky and messy, so stow it all in an airtight bag

The additive is stinky and messy, so stow it all in an airtight bag

Keep some moist towelettes handy to remove the smell from your hands

Keep some moist towelettes handy to remove the smell from your hands

So, besides all the things that I have no way of measuring, like whether the injectors were lubed or water was removed from the fuel tank, was there an increase in MPG? I've compiled the data in the tables below:

With no cetane additive, we drove 1,096 miles and used 50.48 gallons of diesel for an average of 21.71 MPG. With the cetane additive, we drove 1,818 miles, using 76.52 gallons for an average of 23.76 MPG – an improvement of 2.05 MPG! Not bad. But the additive costs money; did we actually come out ahead?

The best price I could find for Diesel Kleen +Cetane Boost was $16.05 for an 80-ounce container, which works out to $.067 per gallon of diesel. So, that increase of just over 2 MPG costs me about 7 cents a gallon. Using a little algebra, I come up with a break even point of $0.70 a gallon – if a gallon of fuel costs more than 70 cents a gallon, I'm ahead of the game if I add cetane to the tank. We haven't seen diesel cheaper than 70 cents a gallon since we sailed to Venezuela in 2002. Another way to look at it is if diesel is selling for, say, $3.13 a gallon, as it is in Las Vegas at the moment, then the cost per mile for fuel drops from $0.144 per mile to $0.135 per mile by adding cetane. If we drive Blue 15,000 miles a year, then we'd save around $135 annually by using cetane – not a fortune, to be sure, but enough to make it worthwhile to a frugal Scotsman like myself.

So, in my view, I'm thinking it's a pretty good investment to use the additive. Whether or not it whitens my smile or shrinks my hemorrhoids remains to be seen. 

This helpful feedback was provided by our good friend, George Swallow, who happens to be an accountant:

Dear David,

The politicians and other state and federal officials talk incessantly about transparency and not to mention accountability and full disclosure.  I just read and analyzed your report of the potential cost savings associated with the use of “Cetane Boosters”.

On the surface, it would appear that your time is well spent if you subscribe to the adage that a penny saved is a penny earned.  I do believe however that there was a flaw in your analysis and the accountant in me feels obliged to point it out.

It does appear that you are not taking into account the cost of airtight plastic bags and moist towelettes.  There is also a cost associated with the depreciation of modified spatulas and the wear and tear of catsup containers.  You might also consider the added cost of fuel to get to a location that sells the afore mentioned booster.  There is also the needed space to store the spatula, catsup container, moist towelettes, air tight bags and (and I repeat) the afore mentioned booster.

You did not mentioned the value of your time to purchase said items, the labor to renovate the spatula, the time to pour the afore mentioned booster into the catsup container and then the added time to pour the afore mentioned booster out of the catsup container.  I suspect I might have left a few other things off the list.

With the extra time on your hands perhaps you could have been able to solve the problems of truly white teeth and shrunken hemorrhoids...just sayin'

Your friend in cost savings,


And my response:

Dear George,

It's so easy for us engineers to overlook the real costs. I also should have accounted for the R&D time needed to develop the modifications to the spatula, and the exhaustive testing that was done to ensure that the ink on the dispenser bottles will withstand the occasional drip of booster solution. Will we need to switch to more expensive alcohol based towelettes in the winter to prevent freezing? Then there's the cost of the accounting time we'll need to calculate the burdened labor costs. But to offset these, what value do we place on our pride in having truly clean, lubricated injectors and the potential of shrunken hemorrhoids? Some things are priceless.


Thanks and grins,