Brief summary - Diesel engine bleeding in 4 steps

• Is the problem solved? Does it need venting because of a dirty filter or empty tank? Then solve this first
• Bleed the pre-filter
• Start the engine and check for leaks for problems
• Bleed the atomizers (if necessary)

Step-by-step instructions for beginners

Step 1: Is the problem solved? 

Why does the engine need to be bled? Is there a dirty diesel filter? If so, replace it first. Has the tank sailed empty? Then fill it sufficiently.

Step 2: Vent the pre-filter

Most boat engines have two fuel filters, and two fuel pumps. We start by following the fuel line from the tank, working our way toward the engine.

Usually from the tank, the first thing you encounter is the pre-filter. That's a fuel filter that often has a sight glass under it. Is the fluid in the sight glass clean? Is it transparent and a little yellow? Then it's good. If it's cloudy, or completely colorless, it's not good. Shine a flashlight through the sight glass to get a good look at the contents.

If the pre-filter is clean, or still empty, we follow the lines to the boost pump. This is usually a mechanical pump mounted on the engine block. In some cases, it is an electric pump suspended next to the engine.

On the booster pump there is a little lever or lever. When we pull it back and forth, we pump the diesel through. Before we do this, we first follow the line further up the engine, to the fine filter. On the fine filter you will find a small screw, usually 10, 12 or 13mm. This is the breather screw. Open this one turn.

After opening the bleed screw, start pumping on the boost pump. The sight glass under the pre-filter should now fill with diesel. We keep pumping until a steady stream of diesel comes out of the screw. Then you can close the screw again.

Step 3: Start the engine and check for problems

Is the breather screw closed again? Then we will now start the engine to see if everything works again. Does the engine immediately start again? Then check that you don't see any more diesel leaking anywhere. Does the engine still not start? Then proceed to step 4.

Step 4: Vent the atomizers (if necessary)

If the engine still won't start, there may be air in the fuel lines to the injectors, the high-pressure system.

Here's how you do this:

• - Look for the metal lines that run from the pump to the engine - these are the fuel lines to the injectors.Loosen the glands (nuts) just a bit at the injectors (circled in red in photo). Usually this is wrench 17.
•  Start the engine briefly.
• After starting for a while, some diesel should squirt out at the unscrewed swivels.
• Stop starting.
• Re-tighten the glands all together.

Notice: Do this only if your engine really won't start after previous steps. Not all engines need this.

Step 5: Check and launch

Check all connections. Restart the engine.

Does it run smoothly right away? Done!
Does it flicker or smoke? If so, it may still have air in it; repeat the steps carefully.

Frequently Asked Questions

How do I know if my engine has been sucking air?
→ Engine starts poorly, runs erratically or stalls shortly after starting.

Is it dangerous to start too long?
→ Yes. You can drain your battery or overheat the starter motor.

Can I prevent air in the system?
→ Refill the tank on time, and keep it clean.

Can't figure it out?

Our technicians will be happy to help you. Visit contact with us to make an appointment.