Yanmar 2GMF - Diesel Fuel Loss

[51RD55]

I just recently changed on my Yanmar 2GMF the fuel filter and the water separator. In the process, I lost about 1.5 cups of diesel fuel of which I was able to return approximately 1 cup full. Much to my surprise, I did not need to bleed the system. The engine started immediately, I ran it for about 15 minutes thinking it would stall when the air bubble eventually reached the injector pump. I ran the engine 3 or 4 times in the course of the day for 10 minutes at a time, revving the engine in the process and still the engine ran beautifully. My question is - is there a self-bleeding mechanism somewhere that would have removed the air bubble or is it possible that there is still air in the system that would cause me a problem in the future? Thanks.

 

[odaydokay]

Cannot speak for the Yanmar's but some of the Universal's (my M-12 as example) are self bleeding. Having said that, when I remove the entire Racor filter (as opposed to just draining its plastic sump), I generally must bleed at the top of the Racor. Maybe if I had waited a long time, it would have self primed, but after 30-40 seconds nothing was cooking so I bled it.

 

[Ralph Johnstone]

Much to my surprise, I did not need to bleed the system. The engine started immediately, I ran it for about 15 minutes thinking it would stall when the air bubble eventually reached the injector pump.

As shown, there is no where for the air to eventually go but to the injection pump.

When you rev the engine in neutral, it moves very little fuel. Once the engine is under load and swaying to and fro (picturesque), you can expect any air bubbles in the delivery system to mobilize and head for the in injection pump.

But mind you, every 1,000 times you change the fuel filters, you do manage to eliminate all of the air. Maybe this is one of those times .

 

[51RD55]

Thank you both for your replies. My husband happened to be speaking with a sailor at the club with whom we have become friends and who has been sailing for 35 years. When he mentioned his concern about our engine, he replied that any air bubble will have gone back into the tank. Well, this sailor is coming along to help us take the boat out for its first sail on Friday. On a different note, we took the first part of a two week course to get our radio licences this evening. It was interesting and we enjoyed it.

 

[HMT2]

When I first started changing the filters on my 2gm I only changed the primary fuel filter and did not have to bleed air. Now when I change fuel filters I always change both the primary and secondary. Whenever I open the secondary filter I always have to bleed air.

 

[Ralph Johnstone]

When he mentioned his concern about our engine, he replied that any air bubble will have gone back into the tank.

This friend sounds like one of those that is often referred to on this site .............. the ones you want to take with a grain of salt. Be careful.

It's highly unlikely that any air will have "gone back into the tank". Air bubbles will always hang at high spots. If you follow your fuel supply hose from your primary filters (the one you changed) back to your fuel tank, you will see the the fuel take-off is on the top of the tank. Inside the tank is a vertical tube which goes down near the bottom of the tank. There is no way for air bubbles to float down through the fuel and into the tank. Scratch that theory.

In addition, if you look at your fuel line leading from your primary filters back to the fuel tank it's most likely laying flat on the bottom of the hull. Additionally, the fuel line going to the engine is likely lying flat as well. Bubbles are not completely removed until the fuel really starts to move.

And lastly, once errant bubbles get past your fuel lift pump, the only way is to go forward, towards the injector pump (as shown on the previous diagram).

If you're worried about a hidden bubble appearing when you least expect it (on the stormy high seas) and not comfortable bleeding the two fuel supply lines at the injectors (back to the diagram), try this:
1. Make the boat fast to the dock and slowly load the engine to a safe level (be careful doing this). This will make the fuel move faster than being in neutral at any RPM.
2. If still no problems, check out how to bleed the engine (check the archives here for some good ideas), but only for a Yanmar 2GM 20F.
3. Head out on a dead calm day and run the engine full throttle to test if there are any bubbles still lurking in the lines.
4. If the engine does shut down, you'll know how to bleed at the injectors.
5. If still no hiccups, you're headed for the open seas.

PS. I'd give anything for a first mate like yourself who takes an interest in engines the way you do.

 

[51RD55]

Would have answered this sooner, but we've both been busy with life and managed to fit in taking a course at our club to get our Restricted Operator's Licence for our boat radio. Took the course one week, studied and this past Wednesday we wrote our exams. We both passed and I thoroughly enjoyed the course. We are big on safety, and it's nice to know how to use the radio properly.
Well, we had our first sail on June 24th, gone for six hours total and we loved it! My husband took a sailing course last September and it was re-assuring to go with our friend who has a few decades of experience and has done some transatlantic crossings (one by himself). Now, I want to learn to handle the sails as well...that will come in time. Another sailor at the club suggested I learn to leave and enter the slip. That wasn't in my thoughts...so will see down the road about that one!
The engine performed perfectly...even went out for two hours the next day with another sailor and all is well with that engine...
Ralph - I'm one of these people who like to know how things work. Sometimes I wish I could live for a few more hundred years, with great health of course, so that I could learn all that interests me. ! LOL