Lifespan of Yanmar 3QM low pressure fuel lift pump

[warmrain]

Our first one died at around 700 hours and we just replaced one (as a part of diagnosing our engine problems) after about 600 hours.

It seems to be the only thing that could still actually be failing and we are going to rig up a temporary electric pump to see if that is our problem as the engine runs fine form a fuel source above the engine.

Has anyone experienced fuel pump failures on new or relatively new mechanical diaphram cam operated pump of this type?

~Cars

[rick_bradshaw]

Steve,

Haven't experience that but our boat came to us with an electric fuel pump in place in addition to the mechanical one. Not sure if this was an "after market" addition or was something they added after having problems.

Hope this helps.

[warmrain]

I am not sure how the post-Hansa boats were configured.

The Hansa boats placed what should have been the primary-filter/water-strainer after the mechanical lift pump. So really the boat has two secondary filters.

The problem with this is when you pressurize and agitate fuel with water in it the water emulsifies and will not coalesce on the paper element and run into the bowl.

We are going to trial an electric pump to help diagnose the problem.

However we are also going to move the primary filter to be the first thing after the tank, we are going to install a vacuum gauge on the output side of that filter and we are then going to put an electric fuel pump in series next (just before the mechanical pump). This happens to be the way my airplane is setup with in series mechanical diaphram and electric fuel pumps.

The plane has a switch for the electric one as it is considered a backup, and you want to know if the mechanical one has failed. We will have to arrange something on the boat so at least once a year we can test the mechanical pump (perhaps by simply removing the fuse for the electric pump).

~Cars