Rajan Wilcox
Running out of diesel can damage your fuel system and be costly to repair. When the tank runs dry, air gets sucked into the fuel lines and must be vented (bled) out. Modern diesel engines built from the early 2000s onwards have a self-bleeding function, but older engines require manual bleeding. To manually bleed the fuel system, you need to loosen the union nuts of each injector, a bleeder screw on the fuel filter housing, or a Schrader valve in the fuel line. You will need a wrench, rags, and a small bottle to collect the primed diesel. After bleeding, refill the tank with fresh diesel fuel, crank the engine without starting it until the fuel lines are free of air, and then attempt to start the engine.
How to start a diesel that ran out of fuel
| Characteristics | Values |
|---|---|
| Fuel injection systems on diesel engines | Very high pressure |
| Fuel system | Requires lubrication |
| Running out of fuel | Risk of damaging the high-pressure side of the fuel system |
| Repriming the pump | Time-consuming and messy |
| Running low on fuel | Can introduce contamination into the fuel system |
| Fuel contamination | Can damage the fuel system |
| Older mechanical engines | Require bleeding lines |
| Modern engines | Self-priming |
| CP4 injection pump | Vulnerable to running dry |
| Self-bleeding function in modern diesel engines | From early 2000s to present |
| Steps to start a diesel engine after it runs out of fuel | Refill the tank, turn the ignition on without starting the engine, turn the ignition off, crank the motor until it starts |
| Fuel system in older diesel tractors or pickup trucks | Requires manual bleeding to restart the motor |
| Process of manual bleeding | Loosen the union nuts of each injector, a bleeder screw on top of the fuel filter housing, or a Schrader valve in the fuel line |
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What You'll Learn
Refill the tank with fresh diesel fuel
Refilling the tank with fresh diesel fuel is the first step in getting your diesel engine running again. However, the process of restarting a diesel engine after it has run out of fuel can be complex and depends on the age and type of engine.
Older diesel engines may have a manual fuel injection system, which means that when the tank runs dry, air is sucked into the fuel lines. This air must be manually vented, or "bled", from the system. To do this, you will need to locate the bleeder screw or bolt, typically found on the fuel filter housing, or the Schrader valve in the fuel line. Loosen the bleeder screw with a wrench, but do not completely remove it. Then, crank the engine without starting it until fuel and air bubbles flow from the bleeder screw. Tighten the screw and attempt to start the engine.
On the other hand, most modern diesel engines built from the early 2000s onwards have a self-bleeding function. This means that the system will rid itself of air without any tinkering under the hood. After refilling the tank with fresh diesel fuel, simply turn the ignition on without starting the engine and leave it in the "ON" position for 30 seconds. Then, turn the ignition off, wait a few seconds, and crank the motor until it starts. If the motor stalls, turn the ignition off and wait a minute before trying again.
It is important to note that running out of fuel can potentially damage your fuel pump, injector pump, or injectors, and it is always best to avoid letting your diesel engine run out of fuel completely.
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Bleeding the 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, hindering the timing of the fuel injection process. This presence of air bubbles within a diesel fuel system is known as an airlock.
Before attempting to bleed the air from the fuel system, ensure you have determined how air entered the system, so it doesn't re-enter after the bleeding process. Air can enter the system by running out of fuel, from leaks in the fuel lines, or after replacing the fuel filter.
To bleed the fuel system, follow these steps:
- Familiarize yourself with the engine and identify the key components of its diesel fuel system, including the fuel tank, fuel lines, fuel filter, and fuel injectors. Review the engine's fuel system layout and connections.
- Turn off the engine and remove the ignition key from the cylinder.
- Locate the fuel filter and determine if it has a built-in bleeder screw.
- If the fuel filter has a bleeder screw, position a clean rag or towel beneath it to catch any fuel spills.
- Use a wrench or bleeder screw key to slowly loosen the screw in a counterclockwise direction. Do not remove it completely.
- If your fuel filter lacks a bleeder screw, you may need to use a Schrader valve in the line or a specific tool for bleeding fuel.
- Pump air into the fuel system via the filler neck, or crank the engine without starting it until fuel and air bubbles flow from the bleeder. Be careful not to crank excessively, as it could overheat the starter or drain the battery.
- Once all the air is out of the system (no more bubbles), tighten the bleeder and attempt to start the engine.
Some additional tips to keep in mind:
- If your fuel level is below half full, you may need to add some fuel to the tank before bleeding.
- Consider replacing your fuel filter if it is old or approaching the end of its life.
- Bleeding the fuel system can be messy, so have some rags or towels on hand to clean up any spills.
- Consult your vehicle's manual to understand the specific ins and outs of your fuel system.
- If you encounter any difficulties or persistent issues, consult a professional diesel mechanic or contact the manufacturer for assistance.
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Check for fuel leaks
Refilling a diesel engine with fuel after it has run out is a delicate process that requires careful attention to avoid damaging the engine. After refilling the tank with fresh diesel fuel, the next step is to bleed the fuel system of air that has accumulated while the tank was empty. This can be done by turning the ignition on without starting the engine and leaving it on for 30 seconds, then turning it off and cranking the motor until the engine starts. If the engine does not start, repeat these steps until it does. If the engine starts but stalls, wait a minute before attempting to start it again. Once the engine starts, allow it to idle for several minutes and check for any signs of fuel leaks before driving off.
To check for fuel leaks, begin by identifying the key components of the diesel fuel system, including the fuel tank, fuel lines, fuel filter, and fuel injectors. Then, locate the fuel filter and determine if it has a built-in bleeder screw. If it does, position a clean rag or towel beneath the bleeder screw to catch any fuel spills, then loosen the bleeder nuts slightly (do not completely loosen or remove them). Crank the engine without starting it until air and bubbles flow out from the bleeder. Re-tighten the bleeder nuts once the system is free of air bubbles.
Another method for checking for leaks is to disconnect the line from the water separator to the lift pump and place the line in a jar of clean diesel below the level of the lift pump. Operate the lever on the lift pump, and if the fuel comes through without air bubbles, replace the line and move on to the next one, working back towards the tank. Keep repeating this process until you've isolated the leaky fuel line, valve, or seal.
A third method for checking for leaks is to create two inline clear sight glasses, one for the fuel supply line and one for the return. Starting from the line before the first fuel filter, suck fuel from the jar. If there are bubbles at the sight glass, move on to the next hose and check for air bubbles again. Repeat this process until there are no more air bubbles, then you will know where the hole is by process of elimination.
It is important to remember that running out of fuel in a diesel engine can be costly as it can damage the high-pressure side of the fuel system. Therefore, it is recommended to always keep an eye on the fuel gauge and ensure that the tank is refilled before it reaches empty.
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Manually bleed out excess air
To manually bleed out excess air from a diesel engine, you must first identify the key components of the fuel system, including the fuel tank, fuel lines, fuel filter, and fuel injectors. Familiarise yourself with the engine and its layout and connections.
Next, locate the fuel filter and determine if it has a built-in bleeder screw. If it does, place a clean rag or towel beneath the bleeder screw to catch any fuel spills. Then, using a wrench or bleeder screw key, slowly and gently loosen the screw in a counter-clockwise direction. Do not remove it completely.
Now, you can pump air into the fuel system via the filler neck using a compressor, or crank the engine without starting it. Continue this until fuel and air bubbles begin to flow from the bleeder screw. Be careful not to crank the engine excessively, as this could cause the starter to overheat or drain the battery.
Once all the air is out of the system and there are no more bubbles, tighten the bleeder screw and attempt to start the engine. If the engine does not start, or there are still signs of air in the system, repeat the bleeding process.
Finally, dispose of any spilled fuel, clean up, and return your tools to their proper location.
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Avoid cranking and re-cranking the motor
Running out of fuel in a diesel engine can be a costly mistake. Fuel-injected diesel engines operate under extremely high pressure and require lubrication. When a diesel engine runs out of fuel, air gets sucked into the system, which must be vented out. This process is called "bleeding" the fuel system.
Modern diesel engines, from the early 2000s onwards, have a self-bleeding function that rids the fuel system of air without the need for manual intervention. However, if your diesel engine does not have this feature, you must avoid cranking and re-cranking the motor. Excessive cranking can overheat the starter or drain the battery.
Instead, follow these steps:
- Refill the tank with fresh diesel fuel.
- Turn the ignition on without starting the engine and leave it in the "ON" position for 30 seconds.
- Turn the ignition off, wait a few seconds, then crank the motor until it starts.
- If the motor does not start, repeat steps 2 and 3.
- If the motor stalls after starting, turn the ignition off and wait a minute before cranking again.
By following these steps, you can avoid potential damage to your engine and ensure a smoother restart process.
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Frequently asked questions
First, refill the tank with fresh diesel fuel. If you have an older vehicle, you will then need to manually bleed the fuel lines of air. If you have a modern vehicle, it may have a self-bleeding function.
Locate the bleeder screw (or bolt) on the fuel filter housing. Loosen it a few turns, but do not remove it. Crank the engine without starting it until fuel and air bubbles flow from the bleeder. Tighten the bleeder and attempt to start the engine.
Most modern diesel engines built from the early 2000s onwards have self-bleeding functions.
Running out of fuel can cause issues with the fuel pump, filter, rail and injectors. This is because the poorest-quality fuel settles at the bottom of the tank, and it’s often full of sediment.
