OOPS!!!
I have the numbers reversed in the above post
the M1-303 is
5 micron nominal (Beta=2, 50%)
18 micron absolute (Beta=75, 98.7%)
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also,
SSLoneStar ,
I have also used WIX filters for years and they are excellent filters. However, if you go by the specs, the new M1-303 followed by the BALDWIN B1441 are the best ones I've found for the Duramax.
When I first bought my 03 Duramax in October 02 I sent emails to AC Delco, Baldwin, Wix and AMSOIL requesting filter % efficiency ratings in microns for their DMAX OIL filters. All responded except AMSOIL.
Here are the numbers I was quoted.
AC DELCO PF2232: 25 microns nominal, 40 microns absolute (Beta numbers not stated)
WIX 57202 13 micron nominal (50%, Beta =2) and 37 micron absolute (98.7%, Beta = 75)
Baldwin B1441: 8 micron nominal (50%, Beta =2) and 23 micron absolute (98.7%, Beta = 75)
AMSOIL SDF-52: No response - May be identical to the B1441 since Baldwin is an OEM for AMSOIL
Since then I also ran accross some data on the Fleetguard LF1610200 for the duramax which has a 10 micron nominal (Beta=2, 50%) and 30 micron absolute (Beta=75, 98.7%) spec.