Because of the ignition quality and high Cetane value of diesel fuels, more consumers are switching to it and opting for diesel-fed vehicles. Some have even caught on to the fact that there is no difference between regular diesel and off-road diesel fuels.
Despite this statement being true, these variants are not interchangeable. Plus, there are serious consequences to mixing them or using them on-road.
Off-road diesel (a.k.a. “cherry juice,” AG or ‘red’ diesel) and regular diesel (a.k.a. EN 590, clear or white diesel) are similar, but they serve different applications and are not convertible. The former is typically used for farm machinery, while the latter is for on-road vehicles.
Despite popular belief, these diesel fuels should only be used for their intended purpose and never arbitrarily.
It does not matter that they are structurally alike or that they can save you a few dollars on fuel taxes — you will have much more to lose if you push your luck in using either inappropriately.
The Origin of Distillate Fuel Oil or Diesel
This fuel variant is a byproduct of the fractional distillation of kerosene but a less volatile type, which works perfectly with the compression-ignition power mill or diesel engine pioneered by German inventor Rudolf Christian Karl Diesel. It is made from crude oil and biomass and is ignited via high amounts of compression instead of spark.
During its early years, diesel was mainly used for aquatic vehicles, construction and utility machines, commercial ships, and submarines. Karl Diesel’s brainchild basically became the forerunner of the Busch-Sulzer powerplant used in U.S. Navy submarines in WWI.
Various manufacturers later developed semi-diesel engines for the peacetime economy. However, they still used the same diesel fuel invented in 1892 — albeit on a “two-stroke cycle at a lower compression pressure” and utilizing a hot bulb for ignition instead of compression.
Why There Is Off-Road Diesel and Regular Diesel
Until the late 20th century, diesel fuel did not have road-related classifications. Every motorist who used the fuel variant could fill up farm machinery or a diesel-powered automobile.
As such, they all had to pay motor fuel taxes regardless of where they rode their vehicle.
However, we can attribute the birth of on-road and off-road diesel to the following series of events:
The advent of mass-produced diesel cars in the 1930s
The influx of diesel-fed automobiles in the market made diesel application no longer exclusive to massive modes of transportation and heavy machinery. For the first time in decades, consumers purchased diesel fuel for use on roadways and highway systems.
Clean Air Act implementation beginning in 1956
Following the boom of the automotive industry and the severity of air pollution, national governments enacted their respective CCAs. The British government led the pack in 1956, and the U.S. followed suit in 1963.
The Clean Air Act also resulted in EPA enforcing stricter regulations on sulfur content in diesel fuels.
IRS’ tax-exemption initiative for off-road diesel in the early 1990s
Almost four decades after fuel taxes were moved from backing emergency and war efforts to funding road construction and similar projects, the Internal Revenue Service decided to exempt off-road diesel from fuel excise tax.
Had diesel fuel not gone mainstream, environmentalists would not have realized that its high sulfuric content gravely added to toxic emissions. And had it not been for this problem, EPA would not have implemented stringent sulfur standards in 2006.
Likewise, manufacturers would not have come up with “Ultra-Low Sulfur” grades or ULSD (more on this later).
The need to distinguish off-road from regular diesel emerged because of tax exemption, federal legislation, improved diesel grades, and reduced sulfuric content in diesel fuels.
At this point, I am guessing your next question would be, “How do I tell them apart?”
Types of Diesel Fuel
Diesel fuel is generally classified as off-road or regular/on-road variants. However, both fuels share too many characteristics.
Hence, it only makes sense to dig deeper into different diesel grades to understand their individual traits. More than the intended use, diesel fuels differ in color, cost, composition, and sulfuric content.
Concerning the latter, the American Society of Testing and Materials (ASTM D975) defines seven diesel fuel grades for different diesel engines.
As for composition, there are currently five main diesel types (alternative fuels included):
- Petroleum diesel is derived from the fractional distillation of crude oil at 200–350 °C (at atmospheric pressure) and used in buses, trains, freight trucks, and construction vehicles.
- Synthetic diesel is produced from carbonaceous material not limited to biomass, biogas, natural gas, and coal has a near-zilch sulfur content — thanks to the Fischer-Tropsch process.
- Biodiesel, made from vegetable oils, animal fats, or recycled restaurant grease and an alternative renewable fuel source to petroleum diesel (referred to as B100)
- Hydrogenated oils and fats (HVO), similar to synthetic diesel but converts ester into alkanes through the process of saponification and can be used in conventional diesel engines
- Dimethyl ether (DME), a diesel variant that boasts high Cetane value, low soot, and reduced Nitrogen Oxide emissions and can potentially be a renewable fuel source
In truth, any of these diesel fuels can be a regular or off-road variant. The diesel grade your vehicle or machinery requires ultimately depends on the type of diesel engine it has.
If we were to ask, “Is off-road diesel the same as regular diesel?” the answer would be a “no” — but only because of the difference in nomenclature and one other interesting factor.
So, how does one determine if it is for highway or non-road use? Let us skip the technicalities and go for the most obvious answer (of course!), which is by color.
Off-Road vs Regular Diesel Comparison Table
| Parameter | Off-road Diesel | Regular Diesel |
|---|---|---|
| Shelf Life | At least 1 year (under cover and in a sealed container), 6—12 months (under other circumstances) | |
| Compression Ratio | Between 14:1 and 25:1 | |
| Sulfur Content | 15—500 ppm | |
| Color | Solvent Red 26 or 164 (IRS 26 C.F.R. 48.4082-1) | Referred to as white or clear diesel |
| Flash Point | Between 52 °C and 93 °C (or 125 °F and 199 °F) | |
| Ideal Rating | At least 45—55 Cetane level | |
| Fuel Blend | B5 (5% biodiesel, 95% petroleum diesel), up to 15% ethanol for e-diesel blends | |
| Ambient Temperature | 0 °C (freezing point), -12 °C (gelling point), 149 °C to 371 °C (vaporization) | |
| Affordability | $1.208/liter or $4.576/USgal (as of 09 Feb 2023) | |
| Application | Equipment and vehicles not operated on public roadways, tractors, bulldozers, emergency stand-by generators, farm or construction machinery | General automobile market, commercial trucking, public and school buses, tractors, cruise ships, heavy equipment, power generators |
From the table above, there is little to no difference between off-road and regular diesel fuels from a composition and chemical standpoint. (Of course, category 3 diesel fuels used in marine vehicles are out of the question.)
Because they are practically similar, there is no better way to distinguish one from the other than by dying one of the diesel fuels a different hue!
Can You Mix Off-Road and Regular Diesel?
Non-road and regular diesel fuels are essentially alike in composition. Hence, you can mix them (provided they are of the same grade and with similar sulfuric content).
However, the answer is not an easy “yes,” as mixing the two variants and using the blend to fill up your daily driver will have legal implications.
In the U.S., the prohibited use of red diesel in commercial or passenger vehicles is a federal law and is subject to penalties and substantial fines when violated.
The same can be said in the UK — although there are certain situations where a non-road vehicle filled with red diesel can pass public roads (for instance, a tractor needing to cross a public road to get to an off-road destination).
This scenario is why governments have decided to dye off-road diesel a different color — it is not merely to distinguish the variant from regular diesel.
Color-coding diesel fuels are the best way for regulating bodies to monitor the proper use of the different diesel fuels (especially since the fuel tax on off-road diesel is rebated).
Naturally, there will be unforeseen emergencies where your only option is to fill an empty tank with the fuel you have. However, you can always prevent this mishap by ensuring you carry ample amounts of spare diesel fuel in your rig.
Conclusion — Off Road Diesel vs Regular Diesel
All in all, today’s guide sheds light on three common questions about regular and off-road diesel:
- What is the difference between off-road diesel and regular diesel? Practically none.
- Can you mix them? Yes.
- Should you? No.
Off-road diesel has been tax-exempted and dyed red for a reason — and that is to help those with businesses and in the agricultural sector save some money from not using public roads.
No matter how tempting, let us not use or even try to mix off-road diesel in our on-road vehicles. The cost savings were intended for these folks — let us keep it that way.
Kris is an avid off-roader and outdoor enthusiast who loves to brave the elements and take on challenging terrain. He also enjoys sharing his passion and knowledge with others so that they, too, can appreciate the ride.
About Kris