Bleeding M25 Series Engines 101- A Summary of Links for You

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Stu Jackson


On the C-310 Group Forum on the website, there was a recent discussion about bleeding M25XPB engines.  

Our C34 "Bleeding Headmaster," Ken Heyman, has contributed a lot of valuable input on this process, particularly his "Theoretical Bleeding" article.  

In this reply on the C-310 board I have organized the key links to Ken's contributions.  One skipper suggested cracking the fuel line to the injectors.  Don't do that!!!

There is absolutely NO reason to crack an injector to bleed an M25 series engine. The M25 needs to manually crack the knurled knob, the M25XP is supposed to be self-bleeding but can be done manually.

The newer M25XPB engines have different wiring than the older M25 and M25XP engines, in that the glow plugs are activated by the key switch which is needed to run the electric fuel pump before the engine starts. Key switch, glow plug, fuel pump runs, glow plugs off to start engine, fuel pump STOPS until oil pressure comes up when engine runs. They changed the wiring with the newer engines. To read the details of this strange newer wiring arrangement, dig your way through this looong thread linked in Reply #1:,5945.0.html, which goes to:,3347.0.html It has a long discussion about how the new wiring works, and concludes with JUST this issue about bleeding.  Critical Upgrades also includes:,5078.msg41829.html#msg41829

As far as basic bleeding is concerned, try these:,2884.0.html,5925.0.html and read the embedded links, especially in reply #5.

There is no need to open the vent or the knob on the Racor, either. Let the electric pump do the work. I end up filling the Racor with injector cleaner.,5558.0.html

Your boat, your choice.

Just don't make what is easy into a hard exercise. Please don't reinvent the wheel, either.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."


Thanks Stu.  I'm planning to bleed my system (changing filters) tomorrow, and came onto the site to look for procedures.  And here was your post!  This would be a great post to put on the maintenance section of the tech wiki.  Thanks again to you, and all the other folks who provide so much information.  It's a friendly and efficient way to share information.  Questions:  I have a Facet electric fuel pump.  It is a cylinder.  There appears to be a twist off section at the lower end.  Is this where the (small) filter is located?  Do I get it off by twisting?  Also, I plan to change both the engine (starboard side) and Rancor filters.  Should I change one, bleed it, then change the other, and then bleed it?  Thanks.

Stu Jackson


1.  Facet pump - There's a nut on the bottom of the pump, and small round tabs that hold the bottom of the pump onto the cylindrical housing.  Just get a wrench on the nut, and slowly turn it.  It will expose the filter and the magnet inside.  Don't drop the magnet.  Remember the Critical Upgrades post about the plumbing - tank, Racor, pump.  You can see the small tabs on the Facet pump in pictures here:,2515.0.html

2.  Racor filter (primary) and secondary (engine mounted).  Yes, do one at a time.  I suggest the secondary first, 'cuz my experience has been you need to loosen or undo the nut on the filter bracket housing to bleed that, although Ken says the pump will "cover that" too.  Give it a try, why not, I will next time I do mine.  Do the filter, bleed it, run the engine so you'll know you have "finished" one before you do the other.  Ron Hill's concept is very valid:  don't do two things at once, ;'cuz if something doesn't work, you just won't know which one is the cause of the problem.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."

Ron Hill

Guys : For what it's worth -- it was Joe Joyce Westerbeke's Service Manager that gave me the idea of leaving the bleed valve cracked about 1/4 turn to have a self bleeding M25 or M25XP engine.  

I did this to my M25XP engine and had no problem for 16/18 years and 5000 hrs!!  A thought
Ron, Apache #788