How to prime a diesel generator?


Priming a diesel generator is a crucial step in ensuring its proper functioning and reliable performance. It involves preparing the generator's fuel system by removing any air pockets and allowing fuel to flow smoothly. This process is essential for initiating combustion and maintaining a steady power supply. Neglecting to prime a diesel generator can lead to various issues, potentially hampering its operation when needed.


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Without proper priming, a diesel generator may experience difficulty starting or fail to start altogether. Air pockets within the fuel system can disrupt fuel flow to the engine, resulting in inadequate lubrication and incomplete combustion. It can lead to excessive wear and tear on engine components, reduced efficiency, and even machine damage over time.

Furthermore, an improperly primed diesel generator can experience fuel starvation, causing interruptions in power generation during critical situations such as power outages or emergencies. The lack of fuel flow can lead to sudden shutdowns and disrupt essential services, jeopardizing operations in various sectors, including hospitals, data centers, and construction sites.

To prevent these issues and ensure optimal performance, understanding and implementing the correct priming procedure for a diesel generator is of utmost importance. By following the recommended steps and guidelines, you can maintain the reliability and functionality of your generator, ensuring an uninterrupted power supply when you need it most.

Understanding Diesel Generator Priming 

Priming in a diesel generator refers to preparing the fuel system to ensure the smooth flow of fuel and proper operation. When a diesel generator is not in use or has run out of 'fuel,' air can enter the fuel system, causing disruptions in fuel flow. Priming involves removing air pockets and filling the fuel lines, filters, and injectors with fuel to enable efficient combustion and reliable power generation.

Priming ensures proper fuel flow and system lubrication in a diesel generator. During the priming process, the fuel system is; purged of air, hindering the generator's ability to start and run smoothly. Proper fuel flow is essential for the combustion process, allowing the engine to generate power efficiently. Priming also helps lubricate the system components by ensuring a steady fuel flow, reducing friction and wear on critical engine parts.

Various diesel generators may require priming, especially those with manual fuel systems or those that have been inactive for an extended period. Some common examples include:

  1. Portable Diesel Generators: These generators often have manual priming mechanisms and may require priming after long storage periods or when emptying the fuel system.

  1. Standby/Backup Diesel Generators: Standby generators, typically used for emergency power backup, may require priming if they haven't been; operated or maintained regularly. Priming is crucial to ensure their readiness during power outages.

  1. Industrial Diesel Generators: Large-scale industrial generators may have complex fuel systems, including multiple fuel tanks, filters, and pumps. These systems may require priming to ensure proper fuel distribution and system functionality.

It is essential to refer to the manufacturer's guidelines and specifications for your specific diesel generator model to determine if priming is necessary and to follow the recommended priming procedures.

Pre-Priming Preparation 

Before starting the priming process, gather the necessary tools and equipment. The following tools are; commonly used for priming a diesel generator:

  • Priming wrenches: 8", 10", and 11" are for the injection pump, 13" for the fuel filter, and 17" and 24" for nozzle lines. These wrenches are; used to open and close the respective components during the priming process. Ensure you have the appropriate sizes for your generator model.

  • Safety gloves: Wear protective gloves to safeguard your hands during the priming process.

  • Safety glasses: Eye protection is essential to prevent fuel or debris from getting into your eyes.

  • Priming pump (if applicable): Some diesel generators may have a manual priming pump. If your generator has one, ensure it is in working condition and ready for use.

Before priming the diesel generator, make sure the generator is turned off and completely disconnected from any power sources. It is crucial for safety reasons and to prevent any electrical accidents during the priming process.

Check the fuel level and quality in the generator's fuel tank. Ensure that the fuel tank has sufficient fuel to complete the priming process. Additionally, inspect the 'fuel' for any signs of contamination or degradation. Contaminated fuel can adversely affect the generator's performance and lead to fuel system clogging. If the 'fuel' is contaminated or has been stored for an extended period, it may be necessary to drain and replace it with fresh fuel before proceeding with the priming process.

By following these pre-priming preparations, you can ensure you have the necessary tools, a safe environment, and suitable fuel to prime your diesel generator effectively.

Steps to Prime a Diesel Generator 

Step 1: Locate the priming pump or manual priming mechanism:

Identify the location of the priming pump or manual priming mechanism on your diesel generator. Refer to the generator's manual or consult the manufacturer's instructions for the specific area of the priming component.

Step 2: Open the fuel supply valve:

Locate the fuel supply valve, usually found near the fuel tank or on the fuel line, and ensure it is not in the closed position. Open the fuel supply valve, allowing fuel to flow through the system during the priming process.

Step 3: Operate the priming pump or manual priming mechanism:

If your diesel generator is; equipped with a priming pump, activate it according to the manufacturer's instructions. Typically, you may need to manually pump the priming pump multiple times to create pressure and force fuel through the system. If your generator has a manual priming mechanism, follow the manufacturer's guidelines to operate it effectively.

*For an electric fuel pump, power the fuel pump by connecting a wire from the battery-positive terminal to the positive terminal of the fuel solenoid at the injection pump to prime the generator. 

Step 4: Continue priming until you see fuel flowing steadily:

Keep operating the priming pump or manual priming mechanism until you observe a steady fuel flow without air bubbles. It indicates that the air has been; purged from the fuel system, and the generator is; adequately primed. Pay close attention to any instructions or indicators provided by the generator manufacturer during the priming process.

Step 5: Close the fuel supply valve:

Once the fuel flows steadily and all air pockets have been; removed, close the fuel supply valve using the appropriate wrench. It ensures that 'fuel' does not continue to flow unnecessarily and helps prevent any fuel leaks.

Step 6: Start the diesel generator and monitor it for proper operation:

Proceed to start the diesel generator following the manufacturer's instructions. Observe the generator's startup process and watch for unusual noises or issues. Allow the generator to run for a few minutes to ensure it operates smoothly without immediate problems.

Step 7: Check for any fuel leaks after priming:

After priming and starting the generator, inspect the fuel lines, connections, and components for any signs of fuel leaks. Pay close attention to joints, fittings, and the fuel filter. If you notice any leaks, address them promptly and ensure the system is; properly sealed before continuing operation.

Troubleshooting and Tips 

Address common issues that may arise during the priming process:

  1. Airlocks: If airlocks persist despite priming, check for any blockages or restrictions in the fuel lines, filters, or injectors. Clear any obstructions to ensure proper fuel flow.

  1. Insufficient fuel flow: If fuel is not flowing steadily during priming, check the fuel supply valve to ensure it is fully open. Additionally, inspect the fuel lines for any kinks or clogs that impede fuel flow.

  1. Priming pump failure: If the priming pump fails to operate or is not generating enough pressure, check for any damages or leaks in the pump. Consider repairing or replacing the pump if necessary.

Provide troubleshooting tips to resolve priming problems:

  1. Ensure proper fuel quality: Contaminated fuel can cause priming issues. Regularly check the 'fuel' for impurities, water, or sediment. If the energy is contaminated, drain it and replace it with clean fuel.

  1. Bleed the fuel system: If air pockets persist after priming, bleeding the fuel system may be necessary. Refer to the generator's manual for the correct bleeding procedure, which typically involves loosening the bleed screws on the fuel filter and injectors until fuel flows steadily.

  1. Check fuel filters: Clogged or dirty filters can hinder proper fuel flow and priming. Inspect and clean or replace the fuel filters as recommended by the manufacturer.

  1. Seek professional assistance: If troubleshooting steps do not resolve the priming problems, it is advisable to consult a qualified technician or contact the generator manufacturer for further assistance.

Offer general tips to maintain and optimize the performance of a diesel generator:

  1. Regular maintenance: Follow the manufacturer's recommended maintenance schedule, including fuel filter replacement, fuel system inspections, and overall generator servicing. Regular maintenance helps prevent issues and ensures optimal performance.

  1. Keep fuel tank filled: Maintain an adequate fuel level to minimize the chances of air entering the fuel system during operation or storage.

  1. Use high-quality fuel: Use clean and high-quality diesel fuel to avoid fuel system problems and ensure efficient combustion.

  1. Store the generator properly: If it is not used for an extended period, properly store it in a clean and dry environment, ensuring the fuel tank is adequate; protected from moisture and contaminants.

  1. Test the generator periodically: Regularly test it by running it under load to verify its performance and identify any potential issues before they become critical.

By addressing common priming issues, following troubleshooting tips, and implementing general maintenance practices, you can maintain and optimize the performance of your diesel generator, ensuring its reliability and longevity.


In conclusion, adequately priming a diesel generator is essential for optimal performance and reliable operation. Proper priming ensures the smooth flow of fuel, efficient combustion, and system lubrication. Neglecting to prime a diesel generator can lead to starting issues, fuel starvation, and potential damage to engine components.

Furthermore, regular maintenance plays a significant role in ensuring the reliable operation of a diesel generator. Regularly inspecting and maintaining the fuel system, including fuel filters and fuel quality, helps prevent priming problems and other issues that can affect the generator's performance. Following the manufacturer's recommended maintenance schedule is crucial for identifying and addressing potential issues before they escalate.

As a final tip, it is advisable to keep a record of the priming procedures specific to your diesel generator model. Note down the steps, any particular tools required, and any troubleshooting tips provided by the manufacturer. This record can serve as a handy reference in case of future priming needs or when assisting others with the priming process. Read, How To Change Engine Oil In A Diesel Generator?

By understanding the importance of priming, emphasizing regular maintenance, and keeping a record of priming procedures, you can ensure the reliable operation and longevity of your diesel generator. Remember to consult the generator's manual and seek professional assistance when needed, to optimize its performance and maintain a steady power supply when it matters most.


FileRehab said…
Nice post, thanks for sharing with us.

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