Originally Posted by mvweebles
Engine manufacturers universally recommend 10 micron ad the on-engine secondary filter is almost always 2 micron.
Perhaps the new(er,) common rail/computer engines are.
The engine mounted secondaries on the older Perkins/Detroit/Cat/Cummins, that I've changed filters on were lucky to have a 10, most were 20, a few were 30.
I always thought it was kind of counterproductive to have a 2, or a 10 filter as a primary when the secondary was no finer, oh well.
I too run the 2s in my Racor
as a primary, the secondary is a 1, (one,) micron.
As far as I know the old Fram dual-cannister units, (that everybody hated and got rid of,) were the only ones I've found in which 1-micron elements are available.
Actually, the old Detroits, where they circulate far more fuel than they use seem to run pretty good as long as you keep the rocks and water
PS, Truth be told, I detest engine mounted secondaries, it's a travesty having filters mounted where even one drop can spill on the engine.
The same for oil