Brian,

The pressure is still the same at the downstream side of the filter as it is anywhere else (assuming something blocks it up to create the pressure) it just has a very low flow rate. Kind of hard to explain but if you took the hose on the downstream side and plugged it up with a pressure guage you would have the same pressure as you do on the upstream side. Anyway, the Oilguard is a very high quality filter, I have one on my F350 and it works great. Oil analysis has always showed low levels of insoluables (soot), less than 0.3% at 10,000 miles. I was using Amsoil HDD 15W-40 at the time because I was driving over 5k a month and didn't want to be changing it all the time. Now I'm using Delo and changing every 5k so I haven't been testing the oil lately.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k