351w oil filter/pressure issue

I have experienced lower than normal oil pressure changing oil and filters
Had a Wix filter and pressure would drop to 15# idle and max of 40 at RPM.
Changed filter and pressure is back up to 20#+ at idle and 50# at RPM.
I put a NAPA Gold filter on(made by Wix) and about 500 miles later I noticed pressure dropping again.
I have to use the stubby smaller filter because of frame clearance.
Before I go to expense of remote filter, any ideas would be appreciated.


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My 365hp 351W has a high volume oil pump setup.
With thin Mobil 1 10W-30 I get between 10 to 20 psi at hot idle; I don't know which gauge is accurate.
My engine was quite until hot; when hot I could hear valve train noise.
I recently installed Mobil 1 15W-50 and the oil pressure is higher.
Now my engine is quite at temperature; I need to put some miles on the 15W-50 to verify if it reduces valve train noise long term. The high performance valve train is more likely to make noise than stock.

The smaller oil filter has less surface area and is more likely to plug up if your engine produces much sludge. I would change small filter on schedule. My 351W does not develop sludge under the valve covers with the Mobile 1. My 289 used to make sludge with conventional oil.

Seems strange the pressure would drop after 500 miles unless your engine oil was hotter, there is some trash in your oil, your filter element has saturated and expanded a bit (increasing pressure drop), your gauge is flaky or the viscosity index improvers are already wearing out.

I apologize for the rambling.

i agree with using a different oil, i also suggest using the wix racing filters way more oil flow through the filter, also if your engine is broken in i suggest putting a bit of lucas oil stabalizer, it will increase oil preasure but also decrease wear on the engine! but i would try a racing filter and a different grade of oil as well first!

I put a couple hundred miles on 351W after switching from Mobil 1 10W-30 to Mobile 1 15W-50 and the engine is running quieter. Perhaps the Mobile 1 10W-30 is a bit thin for my high volume oil pump system.