Rolling Coal 

Rolling Coal for Diesels 

we explain what rolling coal means Working with diesel vehicles, we get requests from time to time to modify a truck to “roll coal.”  Given the recent events in the news, we felt like we should take the opportunity to talk about rolling coal, the environment, the law, and being a good neighbor.

What is “rolling coal?” Rolling coal refers to a couple of different things.  Traditionally, it has referred to modifying your diesel engine to increase the amount of fuel entering the engine.  That results in the truck releasing large amounts of black or gray exhaust fumes.  The reason for the dark color is that the fumes release fuel that has not completely combusted.  


“Rolling coal” is also used to describe the practice of intentionally flooding an area with these sooty exhaust fumes.  People may roll coal on pedestrians, bikers, or other drivers. It is an unsafe practice, which can result in significant injuries to the victims. 


What is the environmental impact of “rolling coal?” 

Rolling coal wastes fuel, which means that your engine is less efficient.  That harms the environment.  In fact, many people who opt to modify their engines in this way do so because they want to take an anti-environmentalism stance.  


How do you make an engine “roll coal”? 

To make an engine roll coal, you need to make modifications that would allow more fuel into the engine than it can use at a particular time.  It is the excess fuel that results in the sooty black exhaust.  Some of the modifications involved in rolling coal include: 

To make an engine roll coal, you need to make modifications that would allow more fuel into the engine than it can use at a particular time.  It is the excess fuel that results in the sooty black exhaust.  Some of the modifications involved in rolling coal include: 

  • Removing the particulate filter 
  • Installing smoke switches
  • Installing smokestacks
  • Increasing the size of exhausts


You can also make your engine “roll coal” through “wet stacking,” which may or may not require engine modifications. 


What is “wet stacking”? 

Wet stacking refers to unburned fuel passing through the engine and into the exhaust system.  People can intentionally “wet stack” by modifying the engine to intact more fuel than it can burn.  However, idling the engine for long periods can also result in “wet stacking.”  

While the term “wet stacking” usually refers to intentional choices to create an oilier, thicker, blacker exhaust, it can also occur due to mechanical problems.  

  • Leaky injectors
  • Over fueling
  • Cold weather 



Is “rolling coal” always intentional? 

It depends on how you define the term.  You can have black exhaust smoke without trying to “roll coal.” Anything that leads to improper fuel burning can result in your diesel exhaust being darker and thicker than usual.  Some potential causes include: 

  • Dirty air filters
  • Faulty injectors
  • Dirty EGR vales
  • MAF sensors
  • Damaged engine rings
  •  Incorrect fuel injection timing
  • Wrong fuel to air ratio
  • Poor fuel quality
  • Excess carbon build-up



Diesel exhaust is not supposed to be thick and black.  A properly running diesel engine should not produce any visible smoke under most operating conditions.  Some exceptions include cold weather, high altitudes, and vehicle start-up. So, if you have noticed a change in the color, thickness, or amount of your exhaust, it could indicate a problem.  The problem could be as simple as a dirty air filter and potentially dangerous as damaged engine piston rings.  The best thing to do is have a mechanic diagnose and treat the problem. 


Does “rolling coal” impact engine performance? 

Manufacturers design engines to run within certain specifications.  “Rolling coal” increases fuel intake outside of the optimal parameters.  Fuel efficiency will decrease.  However, “rolling coal” can improve short-term engine performance.  However, it does so at a cost.  Over time, the practice increases wear and tear on your engine.  



How much does it cost to modify your vehicle to “roll coal”? 

Depending on the modifications a person wants, the process can be relatively inexpensive.  It can cost as little as $200 and as much as $5,000 or more.  Generally, the larger the engine and vehicle, the greater the cost. 


Is “rolling coal” legal? 

No.  The Clean Air Act prohibits the manufacture, sale, or installation of any part for a motor vehicle designed to bypass, defeat, or render inoperable any omission control device.  It even prohibits individuals from tampering with their vehicle’s emissions control devices. 


What does that mean for the typical automobile owner?  The EPA has determined that “rolling coal” is a violation of the Clean Air Act.  However, there are no EPA officials out on street patrol looking for Clean Air Act violators.  The likelihood of an individual with a modified personal vehicle getting hit with a Clean Air Act violation for “rolling coal” in an everyday context seems unlikely.  


In Texas, we used to have a state-wide smoking vehicle reporting program.  However, the Texas Commission on Environmental Quality decommissioned this program.  That does not mean that process is legal in Texas, but it reduces the chances of prosecution.  Texas police do not write traffic violations for “rolling coal.” We were unable to find any instances of someone being prosecuted for it.  


While it seems unlikely that individuals will face criminal punishments for “rolling coal,” manufacturers and installers of those devices face a greater risk.  The Discovery Channel had a TV show called Diesel Brothers, which featured diesel enthusiasts who produced and sold trucks that they had modified to “roll coal.”  The court ordered them to pay an $851,451 fine for their Clean Air Act violations.  


It also seems possible for someone who intentionally “rolls coal” onto another person to face criminal charges.  According to Elton Mathis, the Waller County District Attorney, “rolling coal” onto another person could be considered an act of assault.  

We are mechanics, not lawyers.  Our takeaway is that modifying diesel engines to “roll coal” is a practice that puts both the installer and the vehicle owner at risk of possible prosecution or fines.  


Why is “rolling coal” in the news? 

While diesel enthusiasts have known about “rolling coal” for a while, two recent incidents have made the general public aware of the phenomenon.  


On September 25, 2021, in Waller County, Texas, a Texas teenager hit six cyclists.  He seriously injured three of them, while three of them had minor injuries.  The police did not arrest the teen or charge him with any crimes.  However, Waller County has appointed a special prosecutor.  


“Coal rolling” is part of the story because the teen was allegedly harassing the cyclists before he hit them.  According to other cyclists in the group, the teen had “rolled coal” on them and was trying to position himself to do so again when he collided with six of the cyclists.  People have been outraged about the lack of charges since the boy struck the cyclists with his truck. The discussion of “coal rolling” has focused on the idea that he was intentionally harassing them.


Then, in October 2021, a “coal rolling” Tik Tok video went viral.  In the video, a truck backs up to the door of a Whataburger restaurant and intentionally “rolls coal” into the building full of people.  While some of the kids seemed to laugh while running from the smoke, not everyone was amused.  


What do we think of “rolling coal?”

It is fair to describe us as diesel enthusiasts.  Some of the folks in the shop love the look of the black smoke at a sledding competition.  However, as mechanics, our goal is to keep your engine well-maintained and running properly.  If you are accidentally “rolling coal,” come in and let us get your car or truck running properly.