Bleeding Your Diesel Engine

November 1, 2023

Diesel engines include various components that are responsible for pushing fuel from the fuel tank into the injectors, including filters, supply lines and the injectors themselves. When air gets inside these fuel supply parts, your engine could experience some trouble operating at full capacity. To avoid unnecessary problems, it’s essential to know how to bleed your diesel fuel system to flush all air from your engine. 


What Is Bleeding an Engine?

Bleeding your diesel engine involves extracting air from inside a car’s fuel system. Diesel fuel systems are designed to maintain pressure ratings from 10,000 pounds per square inch (PSI) to 30,000 PSI. This pressure is necessary to pump the fuel into the engine, allowing it to function correctly. Air can prevent the buildup of sufficient pressure, which hinders the timing of the fuel injection process. 

This presence of air bubbles within a diesel fuel system is known as an airlock. Airlocks commonly occur following routine maintenance to the fuel line, fuel filter replacements or when your fuel tank runs out of fuel. Bleeding your engine after these occurrences will ensure it runs at its best. While many modern vehicles are equipped with self-bleeding capabilities, a manual bleed is often a safer option. 


Symptoms of an Air-Locked Engine

Your engine requires a steady supply of high-quality fuel, which the fuel system is responsible for providing. When air gets into your gas or diesel system and makes it more challenging to supply clean fuel, your engine’s performance can become compromised. 

In most cases, you’ll have a good idea of when an airlock is likely to occur. You’ve either run the tank dry, replaced your fuel filter or adjusted your fuel line. Airlocks can also happen when there is a small leak in your fuel system. If you aren’t sure whether you have a leak, keep an eye out for some of these common symptoms of an airlock in a diesel fuel system’s engine: 

  • Running with poor efficiency
  • Starting roughly or not at all
  • Not reaching full power
  • Releasing black smoke


How to Bleed Air Out of a Diesel Fuel System

Bleeding the air out of your fuel system requires forcing fuel through and pushing the trapped air out. Typically, bleeding most engines requires following a specific order, usually starting with the secondary filter before moving to the injector pump and injectors. Make sure you refer to your vehicle’s manual, which will greatly help you understand your system’s specific ins and outs. 

If you’ve run out of fuel, ensure you add some before starting. Once you’re ready to go, you can follow the steps outlined below: 

  1. Cover all venting units to prevent spills. 
  2. Locate and open the bleed plug on your secondary filter. 
  3. Open the fuel supply valve. 
  4. Use the manual pump to prime your diesel engine by pushing fuel through your system.
  5. Pump multiple times until you see a steady flow of fuel. 
  6. Tighten the bleed plug. 
  7. Attempt to start your engine and evaluate its condition.
  8. Repeat steps for the primary filter, fuel pump and injection lines if the engine doesn’t start or runs poorly.


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Explore our product offerings and purchase your gasoline or diesel fuel system additives today. You can also contact us online with any questions or concerns.