Not long ago I received the following note from a reader; it echoes questions I’ve been asked on this subject literally hundreds of times, and as such, bears sharing with as wide an audience as possible. The subject is both vitally important, yet frequently misunderstood.
“I have a Sabreline 36 Sedan with twin 6LYA-STP Yanmar 370hp engines.
The on-engine filters are standard Yanmar. I have Racor 900MA turbine primary filters. I currently use 2 micron elements and have a pressure drop of 2–3 inches of mercury [a standard vacuum unit of measure] across the Racors at wide open throttle. My mechanic says that I should only be using 10- or even 30-micron filters in the Racors and that by using the 2 micron ones, I am damaging my engine fuel lift pump and perhaps the injector pump. Is he correct?
I maintain that the filters are rated for my engine’s flow rate (about 66gph max) and as long as the pressure drop across them is less than 15 inches of mercury and I can reach rated rpm (3,300) at wide open throttle (W.O.T.), I am OK. Is there any way to tell if the lift pump or the injector pump is performing normally or if they have been damaged?”
This is a great question.