Stretch,
Something I came across while investigating employing 2 micron fuel filters.
"Racor's 2 micron filter medium should only be used in final or secondary filters where the fuel is first filtered by a primary filter. The primary filter for a 2 micron final filter should use a 10 micron medium. The exception in using a 2 micron filter in place of a primary filter is to obtain high-efficiency water separation, and is usually used in marine applications where the fuel supply may be cleaner but also may contain water more often. If the installation can allow the use of a filter large enough, then a 2 micron filter can serve in a system as the only filter in that system"
I'll get back to you on what the Yanmar people say!
Cheers!
The above quote is taken out of context -
warning !!!!!
There is no NEED for a 2µM filter on any Yanmar or other small marine diesel.
Typical maximum filtration for a 'historically dirty' fuel system is: tank --> 30µM --> 10µM --> engine mounted 'guard' filter @ 15-17µM --> engine.
Yanmars and most other marine diesels are designed around 'the 20µM as the most damaging particle concept'. As previously stated by others, these filters are not all that efficient in partical removal and can pass particles much larger than their 'rating'.
Why 20µM and filtration to 'protect at less than 20µM?
2 reasons:
1. 20µM has been found to be historically the most damaging particle in diesel engines.
2. your injector tip has an equivalent orfice diameter of ~100-125µM and to ensure that particles wont 'bridge' across the orfice thus blocking it, history shows that you need a 20µM filter.
Most 'orfices' need to be protected by filters etc. that can remove particles that are 1/4 to 1/5 the size of that orfice ... or they usually become blocked.
A 2µM rated filter will have 5-10X the 'flow rate restriction' of a 10µM .... meaning that if you replace a 10µM with a 2µM (for any reason) and to have the exact flow conditions of the original 10µM, you will need into INCREASE the surface area of the 2µM by FIVE TIMES (or need 5 times as many 2µM installed !) .... or you will experience 5 TIME the differential pressure across that 2µM and will need to change the 2µM five times more ofter.
Further, a 2µM is a quite bad idea as most 'particles' in contaminated diesel fuel are 'soft' and easily deformable and with smaller particles in nature there will be exponentially more of them present in the fluid .... and upon increasing differential pressure on a filter can 'extrude' right through a 'tighter' filter than the 'usual' 10µM (or the normal engine mounted 'guard' filter).
With extrusion of soft 'gels' and other deformables (the typical debris from 'bio-contamination'), expect to be cleaning 'coked-on carbon' deposits a LOT more often from your exhaust system as these soft particles do not burn very well in the combustion chambers. With lower operating pressure drop across a 10µM, it will better 'retain' the soft/deformables.
30µM (if you normally get a lot of 'hard' crud from your tank) --> 10µM --> 15µM in the small engine 'guard' filter --> engine.
;-)
