Brian, as a high volume user of JD engines, I'm sure you're aware of JD's position that anything more restrictive than a 30 micron primary filter is not recommended.  In fact, JD doesn't even appear to support Racors at all.  When my JD 6068 experienced fuel pressure problems, JD made the local JD service technician by-pass the Racor to make sure that wasn't the problem.

In the past I was a supporter of 2 micron primaries and to just change the secondary engine mounted filter annually.  After all the Racor cartridges were much expensive than the $35 Yanmar filters and a whole lot easier to change in any condition. And a vacumn gauge and visual inspection will give me forwarning of primary filter problems when there isn't an equivalent forwarning for secondary filters.

Now I've reconsidered, but done so without factual evidence yet to support my current thought process.  I now use 10m primaries and am considering JD's recommendation to use 30m primaries.  My new thought process is based on my assumption that the amount of trash in the 3 to 10 or even 3 to 30 micron range is probably insignificant.  If this assumption is true, the amount of sub 10 or 30 micron junk that gets by the 10 or 30 micron primary will not be so much that the secondary filter will ever require changing more often than recommended by the manufacturer.  Obviously, well at least I think it's obvious, that a 10 or 30 micron primary filter will not clog as soon as a 2 micron primary filter.

Although I don't have engineering evidence to support my new thought process I do have some practical experience.  My new boat's first load of fuel was bad.  It would clog, or nearly clog, a 2 micron primary filter in less than 20 hours.  So I changed to a 10 micron primary.  Doing so doubled the amount of time it took to clog the primary.  After changing primaries 3 times (twice they where 10 micron units) I changed the secondary 2 micron JD filter and it appeared clean.  I did have the tanks professionally cleaned at that point, so I can't effectively do a similar test with 30 micron filters.

As someone else pointed out, this topic and the twin vs single engine topic are like comparing dogs and cats.  Well, maybe not, dogs are better pets than cats--aren't they :-)

Gil
"Dog's Life"
OA Classico 50
Get on board. You're invited to try the new Yahoo! Mail Beta.

If you are a fan of "experience rating" the 2 micron filter issue, I've got
over 8,000 hours on my Lehmans and had the same injectors and injector pumps
for 16 years. I've only had one bad load of fuel which took 6 filters to get
through.

Boston Injection charges over $800 to rebuild the injector pumps so I look
at clean fuel as a "cost avoidance" maintenance item...

                                      Regards....

Phil Rosch
Old Harbor Consulting
M/V "Curmudgeon" MT44 TC
Currently lying Bond Creek, NC