There are many reasons why you might need to bleed your diesel engine, and few of them are good: You’ve run out of fuel, the fuel filters are clogged with dirty fuel, you’ve had to replace a secondary filter. If bleed you must, and sooner or later, unless you have a new high-tech common rail engine, you’ll probably need to get the air out of the system manually sooner or later. Take a look at this fast guide and then practice bleeding your diesel while you’re still at the dock, so you have this drill down perfectly. It will be much easier there than to try this for the first time five miles offshore while the boat is rocking and pitching. It’s also a good idea to mark the wrench you need for this, just to save time.
For a lesson, or a refresher course, take a look here: http://www.yachtingmonthly.com/sailing-skills/things-practise-harbour-bleeding-engine-61070