Our path south to the Bahamas takes us against the prevailing winds which tend to blow from the south east up the East Coast of the USA. To make our schedule we need to use the diesel engine more than we would like.

To keep our trusty thirty five horsepower Yanmar 3HM35F diesel engine running smoothly, I change the primary fuel filter monthly. Our primary fuel filter keeps the water and gunk out of our secondary fuel filter. The secondary fuel filter is a Yanmar part which both harder to replace and only available from Yanmar dealers. Our primary fuel filter is a Racor 500FG with a 30 micron filter. In the US you can pick up Racor filters in almost every marine supply store.


Racor 500FG fuel filter assembly

Usually when I replace the Racor filter I prime the filter with diesel to prevent air getting into the fuel system. On Wednesday I skipped this step because it looked like the Racor’s bowl and plenty of diesel in it. Frankie was close on hand and I was trying to save time.  So on Thursday when we powered up the engine in preparation to move to Spa Creek for the Annapolis Boat Show staff party it ran beautifully for about thirty seconds before shuddering to a stop.

Most day to day problems with diesel engines can be traced to fuel supply. In this case, I knew immediately the probem was air in the fuel lines because I knew I had taken a dumb shortcut when changing the Racor filter. My first opportunity to bleed our engine! I was kind of excited because bleeding your engine for the first time is a rite of passage for crusing “sailors”.

Mary and I have known since we left Duluth that we needed to know how to bleed our engine.  I had done some maintenance work on the diesel engines in heavy machinery and trucks while working in the Northern Territory of Australia in the mid 1990s and had a vague idea of what to do. I had owned a 1950s Farmall M tractor in Minnesota.  I had also watched lots of Youtube videos of people bleeding diesel engines on sailboats. How hard could it be?

I started by priming the Racor filter.  I then tried turning the engine over. No luck.

The second step was to  push air out of the fuel line to the secondary filter. There is a handly little manual lift pump on the side of the engine:


Manual lift pump

I moved the lever on the lift pump up and down to pump diesel through the lines. I slightlly loosened the bleed screw on the secondary filter.


Bleed screw on secondary fuel filter



Bubbles came out, confirming there was air in the fuel lines. But I was getting impatient with the little lift pump. Our engine has an electric lift pump to draw diesel out of the fuel tank up to the engine so I turned the engine over to get some fuel pumping through the lines.


Electric lift pump

Diesel squirted out of the bleed screw. Great. Tightened up the bleed screw and turned over the engine again. No luck. Bummer.

The next step was to bleed the injection pump.

Bleed screw on injection pump

Bleed screw on injection pump

I loosened the bleed screw. This time I  just turned over the engine until diesel squirted out of the bleed screw. I then tightened the bleed screw. Turned over the engine and it leapt into action.

Cheers and high fives all round.