The Stovebolt Site Forums The Shop Area Engine Shop oil filter equates to pressure drop

A few years ago I installed new custom made 'Airequip' hoses to and from my oil filter canister on my 235. I noticed over time there was a drop in oil pressure at all engine speeds. I blamed my original gauge for reading wrong and installed an aftermarket unit. My original gauge seemingly read correctly.
At speeds of 35-40 MPH I was reading about 25-30 PSI. Idling at traffic lights it went down to 10 PSI.
Today I removed the oil filter assembly and plugged the holes in the block. A test drive at normal operating temps gave me a 40-45 PSI reading at speed and nothing less than 25 PSI at idle.
I know by-pass oil filters can rob your oil pressure a bit but not this much. The only thing I can think is that the inner diameter of the 'Airequip' hoses was too large. It was probably a good 1/8".
Anyway as I change oil every 1000-1500 miles I think I'll leave the filter off the truck.

You actually had plenty of pressure for your engine with the oil filter. They always used to say 10 psi for every 1000 rpm, and and you had more than that.

If I were you, I would connect the lines again so you are filtering your oil.

The bypass filter actually does a better job of filtering than a full flow filter.

The oil flow through the bypass filter is regulated by a small hole on the hollow tube inside the housing. I believe it's about 1/16" dia.
Maybe a previous owner made yours larger to get 'better filtering'.
Flow is always as good as the smallest opening in the system allows, unless the filter is clogged.

If I plug the bypass filter on my 235, there is no change in oil pressure.
But it's not new and never gets up higher than 35 lbs. hot with SAE 30.

Quality full flow filters keep particles larger than 15 microns away from main bearings.
Some bypass filters clean the oil down to fractions of 1 micron.
Both together are ideal. None keeps particles of any size suspended in detergent oil until it is drained.

Changing your oil as often as every 1000-1500 miles should not require any filtration and the modern oils don't have the high parafin content of yesteryear so sludge should be a problem either.

On the road again - I examined the filter canister and both the inlet and outlet holes are large, probably 1/4". The hollow tube in the center has 2 holes about 1/8" opposite each other near the top.

Holes that big everywhere will definitely drop your oil pressure. I'd suggest threading the inside of a fitting on one of the flex lines, and experimenting with Holley carburetor jets until you find one that gets the pressure up where you want it while still providing enough flow for good filtering. I'd suggest a jet with about a 1/16" hole in it.
Jerry

There might be a reducing fitting too I believe.