Diesel Fuel Grades

#1, #2, Winterized, & Ag Diesel Explained

Diesel fuel is commercially available in multiple grades and types, although the differences between various grades do not correspond to any significant compatibility issues with respect to engine operation. Each grade of diesel fuel has its own advantages and disadvantages, giving up certain characteristics in order to gain others. #1 diesel, for example, has a lower energy content than #2 diesel fuel, but does not have the same tendency to gel in cold weather environments.

#1 vs #2 vs Winterized Diesel

#2 diesel fuel is readily available and the most common grade of diesel at fuel stations. #2 diesel has the highest energy content and lubricity properties. The high energy content translates into the best possible performance and fuel economy, while the lubricity of #2 diesel protects injection pumps, seals, and other engine components. It is also typically less expensive than #1 diesel, as it does not require the same depth of refinement to produce. The downside of #2 diesel is that it has a tendency to gel (thicken) at a higher temperature than #1 diesel. Fuel gelling leads to hard starts, no starts, and related complications in cold environments.

#1 diesel fuel has a lower energy content (on the order of 5%) than #2 diesel and is typically more expensive. However, it does not gel in cold weather like #2 diesel because the paraffin (a type of wax) has been removed from the fuel. While this keeps the fuel flowing in cold weather, paraffin is an important lubricating compound found in #2 diesel.

Winterized diesel fuel is a blend of #1 and #2 diesel fuels, typically on the order of 15-20% #1 diesel by volume. Winterized fuel blends are released when the weather becomes too cold for #2. By combining both types of diesel, the fuel contains adequate energy content and acceptable lubrication properties while reducing the risk of fuel gelling due to cold temperatures. Fuel economy typically drops slightly during the winter do to the decreased energy content of winterized fuel blends.

Running #1 diesel will not cause any immediate concerns, though prolonged use in an engine designed to run on #2 diesel may reduce fuel system life in the long run. Obviously, #1 and #2 diesel fuels can be mixed, and you shouldn't be afraid to fill up with #1 if that is all that is available to you at the time.

#1 Diesel Fuel

#2 Diesel Fuel

Lower energy content

High energy content

Lower lubrication properties

High lubrication properties

High resistance to "gelling" in cold weather

Lower resistance to "gelling" in cold weather

Off-Road Diesel (AG) vs Highway Diesel

Off-road diesel (ag diesel, red diesel) is available for vehicles and equipment that are not operated on public roads. As such, it is not subjected to many of the taxes that highway diesel is (taxes on highway diesel vary by location) and therefore the cost of off-road diesel is significantly lower. Off-road diesel is intentionally dyed red so that it is distinguishable from highway diesel, as it is illegal for use on public roads/highways.

Authorities can easily test for illegal use of off-road diesel by the "dip test", in which they dip an apparatus into the fuel tank to check for unlawful use off-road diesel. While the temptation to find a source of cheaper red diesel may be high, the fines are steep and can run thousands of dollars per offense. Chemically speaking, off-road diesel today is the same as highway ULSD, with the exception of some industries (including marine and locomotive sectors) that may still have access to LSD. Today's off-road diesel maintains no advantage, save for price, over conventional on-highway diesel.


Low sulfur diesel is classified as diesel fuel containing no more than 500 ppm (parts per million) sulfur content, while ultra low sulfur diesel must maintain no more than 15 ppm sulfur content. As of 2007, the EPA has mandated that all highway diesel fuel sold in the United States must meet ULSD specs. Sulfur, combined with other elements found in diesel fuel, acts as a natural lubricant for fuel system components, such as seals and pumps. However, it also contributes to high particulate emissions (exhaust soot), and thus the mandate was a necessary move in the progression of reduced emissions.

Modern emissions components, including diesel particulate filters (DPF), are only compatible with ULSD, while older engines may require the use of a fuel additive in order to supplement the lubricity lost in ULSD. ULSD has a higher cetane rating than LSD, though its energy content is slightly lower. LSD remains available in some industries, though this is unlikely to last given the current crackdown on emissions in the United States.

Biodiesel vs Petroleum Diesel

Biodiesel is a renewable source of diesel fuel produced from organic materials (such as vegetable oil) through a refining process called "esterificiation". It is available in pure form, or as a blend of biodiesel and petroleum diesel fuels. Biodiesel is classified based on the percentage of its biodiesel content, such that B100 refers to pure biodiesel (100% biodiesel). B5 and B20 are common, commercially available blends containing 5% biodiesel/95% conventional diesel and 20% biodiesel/80% conventional diesel respectively. Biodiesel of any blend or pure form is legal for use in all highway and off-road applications. However, most engines are not certified for B100, and there is some controversy over the long term effects of sustained use of pure biodiesel.

Biodiesel has a higher cetane rating than conventional diesel, significantly lower hydrocarbon and particulate emissions, but at the expense of a slightly lower energy content (thought effects on performance are minimal) and greater NOx emissions. In many instances, biodiesel is also less expensive than conventional diesel. Additionally, biodiesel is particularly susceptible to gelling in cold weather, though the effect is of primary concern in its pure form. Lower particulate matter emissions (exhaust soot) when using biodiesel translates into less regen cycles in DPF equipped applications. Should you decide to run B100 in your diesel, it is recommended that the fuel filter(s) be changed after running the first tank, as biodiesel may dislodge deposits left from petroleum diesel.

Biodiesel (B100)

Petroleum Diesel

Low greenhouse gas and particulate emissions

High energy content, better performance and fuel economy

Refined from renewable resources

High resistance to gelling in cold weather

Often less expensive than conventional diesel

Safe for all fuel systems