Here is the response I got from Racor
Kevin,
The OEM filter is 99% efficient at 4 microns and larger.
There is no accepted SAE or ISO test to determine efficiency at 2 microns,
as the silica dust used in testing is not calibrated down to 2 microns.
More efficient media would have very, very short life.
In general, only 1 percent of particles 4 microns and larger get though the
filter to the injectors. Under "normal" on-road driving conditions, the
injectors are perfectly protected.
However, if the truck is run in very dusty conditions, the diesel fuel can
get contaminated with a huge number of particles. One percent of billions
of particles means a lot of particles still get through to the injection
system.
The first line of defense is to know your diesel fuel source and be aware
that it is very easy to contaminate diesel fuel.
To counter high particle load (dusty) operating conditions, a pre-filter
should be used. A pre-filter might pass 1 percent of the particles to the
OEM filter, which would in turn pass only 1 percent of those particles.
The 100 of 1 reduction in particles means the injectors are again
protected.
In the next few weeks, Racor will announce a pre-filter kit with a heater
option, and water sensor hook-ups to the truck electronics. Currently,
about 10 pre-filter kits are being tested in Canada.
It is up to you if you want to wait for this kit. If you drive in very
dust conditions, and you have had poor diesel fuel quality problems, then
you may not want to wait.
Best regards,
Steven Hardison
Product Manager
Racor Division Parker Hannifin Corp
3400 Finch Road
Modesto CA 95353