How To Tell if a Truck Is Diesel

One way to determine if a truck runs on diesel is by its loud and rough engine sound and the amount of black smoke it produces. Another clue is the black tailpipe. Other indicators include labeling that says “Diesel” or “CDL Required,” a big engine, high torque, and manufactured by a company specializing in diesel engines. If uncertain, ask the owner or driver.


Color of Diesel and Gasoline 

Diesel and gasoline have similar natural colors of clear, white, or slightly amber. The color difference comes from additives, with dyed diesel having a yellowish tint and gasoline additives being clear or colorless.

Characteristics of Diesel Fuel 

Diesel fuel is a petroleum-based product known for its high energy density and ability to produce torque. Its color varies, with most types having a slight yellowish tint, depending on the crude oil used and the additives included during refining.

Risks of Putting Gasoline in a Diesel Engine 

Gasoline and diesel are different fuels, and even a small amount of gasoline in a diesel engine can cause serious problems. Gasoline lowers the diesel flash point, leading to engine damage, fuel pump damage, and injector problems. At times, it may cause the engine to seize completely.

Differences between Unleaded and Diesel 

Diesel and unleaded gasoline come from crude oil, but diesel goes through a distillation process, while unleaded gasoline does not. Diesel contains no lead and is more fuel-efficient but produces more emissions. When choosing a fuel, consider the trade-offs between mileage and emissions.

Why Dyed Diesel Is Illegal 

Red diesel, a fuel not taxed, is illegal for use in on-road vehicles. Using red diesel in on-road cars can result in substantial fines, with distributors and fuel retailers liable if they knowingly supply it to on-road vehicles. Always use tax-paid fuel to avoid legal and financial consequences.

Green and White Diesel 

Green diesel is dyed with Solvent Blue and Solvent Yellow, while white diesel does not contain dye. Green diesel is used for commercial purposes, while white diesel is used for domestic purposes. Both are safe and provide excellent fuel economy.

What Good Diesel Should Look Like 

Clear and bright diesel is the desired fuel. Diesel should be translucent like water, whether it’s red or yellow. Cloudy or sedimented diesel is a sign of contamination, which can cause equipment to run less efficiently and incur long-term damage. Always check color and clarity before fueling up.


Knowing whether a truck is diesel or not holds significant importance for various reasons. As a motorist, you must ensure you’re putting the right fuel in your vehicle. As a business owner, you must ensure your vehicles use tax-paid fuel. Additionally, having knowledge about diesel engines can prove helpful in distinguishing them from unleaded gasoline. Understanding these key differences can help you ensure your vehicles run efficiently and legally.

About the author, Laurence Perkins

Laurence Perkins is the passionate car enthusiast behind the blog My Auto Machine. With over a decade of experience in the automotive industry, Perkins has knowledge and experience with a wide range of car makes and models. His particular interests lie in performance and modification, and his blog covers these topics in-depth. In addition to his own blog, Perkins is a respected voice in the automotive community and writes for various automotive publications. His insights and opinions on cars are highly sought-after.