Marine Engines: Dealing with Air the Fuel Line

22 November 2017
 Categories: , Blog


The diesel engine on your boat plays a key role in ensuring that you can safely navigate the oceans. However, now and again, your engine may experience a problem. Knowing how to solve these problems while out on the water can allow you to restart the engine so you can continue your voyage. This article will look at the problem of air entering the fuel line.

The 3 signs that air has entered the fuel system

If air enters the fuel system of your diesel engine, you may notice the following signs:

  • Reduced engine power
  • Uneven engine sounds
  • Engine failure

The cause of the problem

The most likely cause of this problem is a faulty seal on an injector pipe. The injector pipes on your boat's diesel engine are responsible for compressing fuel and spraying a small amount into the combustion chamber. If air enters the injector pipe, it will absorb the energy of the piston as it attempts to compress the fuel, reducing the amount of fuel which is supplied to the engine. Thankfully, this problem can be easily solved by bleeding the fuel system to remove any trapped air.

The solution to the problem of air in the fuel system

Your fuel system should have a number of bleed valves located high up at the top the fuel pump and the filter. By opening these valves, you can release any air which has become trapped in the system. Simply remove the screw from each valve and it open, allowing the air inside to escape. If you have trouble locating the bleed valves, you should refer to the boat's technical manual. Ideally, you should have located these valves and splashed a dab of bright paint next to them so they can be found easily when at sea in low light conditions.

Once these valves have been opened, you should wait a few minutes for the air to escape. Gravity pulling fuel through the system should push the air out once the valves are open. You should never attempt to pump fuel through the system by hand or use the starter motor to try and get things moving. Doing so will only draw more air into the system and cause further problems. Once you get back to shore, you should have the seals on the fuel system inspected and changed to prevent future air leaks. 

For more information, contact a company which specialises in marine engines.