Whenever you pull up to a fuel station, you will surely notice the different tiers of gasoline available at the pump. Each option – Regular, Super, and Premium comes labeled with its own plainly visible octane rating.
Diesel, on the other hand, is nearly always just one pump but on most you will notice a cetane rating. Both octane and cetane ratings are on a scale from 0-100, and while you’re right to assume, much like octane, a higher number is better; they actually work in opposite ways. In this guide, we will cover all the essential details you need to understand regarding this rating.
What it is:
With gasoline the octane number refers to how resistant the fuel is to auto-ignition. Since diesel engines rely on compression and not a spark to ignite fuel, the cetane rating refers to the speed at which the diesel fuel ignites under compression. A higher cetane number means the fuel ignites sooner after injection. This helps engines start sooner and run smoother. This is especially helpful in the colder months when diesel engines start and run a little harder. Running with a proper cetane rating will result in more complete combustion, which can help keep ignition components cleaner.
Understanding the number:
While companies like VW and Mercedes don’t recommend a cetane rating, in the US the minimum number required for fueling stations is 40. Since cetane rating is a time-based rating as opposed to octane being a resistance rating, most diesel engines are designed and made to run at a rating of 40 cetane.
What to do:
Although as discussed earlier, the higher the number the better for cetane, trying to chase the number as close as you can to 100 is certainly more of a fool’s errand. While it is perfectly safe to use the minimum rating of 40, boosting it a few points does have its benefits.
There are lots of products that solely boost your cetane. However we recommend using products like Opti-Lube, which provide a mix of features such as anti-gelling and lubrication, and on top of those will also naturally boost the cetane rating a few points. The increase will help your diesel start better in the winter as well as run smoother and reduce emissions.
The bottom line:
The minimum cetane rating of 40 or above is perfectly adequate for standard diesel engines. However, utilizing additives for minor cetane increases can improve engine smoothness and provide better performance in cold weather. We recommend utilizing an additive such as Opti-Lube because its formula is well-rounded for the needs of a diesel engine and will offer improvements beyond just cetane.
