Name Deleted made the helpful observation that substituting a larger oil filter may change the bypass characteristics because the specifications on the by-pass valves may be different. Actually the valve specifications are identical, but the larger filter will have less resistance at the same flow rate and therefore it will open at a higher rpm.
As an example say the small oil filter starts to by pass at 2000 rpm. If a larger filter can delay that opening to say 2500 rpm that means that means an V8 owner in OD can delay opening the by pass valve from 55 mph to 69 mph. Think of a long trip, it would better to filter all the oil the whole time than by-pass much of it. You will arrive with much cleaner oil without slowing down. At say 4000+ rpm both filters will bypass most of the oil so any size advantage disappears.
But the choice to run the big filter in the stock location is not a simple one. A larger filter is about a ½" closer to the exhaust pipe in V8 SHOs and you risk baking your oil. Heat is the enemy of oil. How real is the problem? I don’t know, Paul Nimz made a nifty heat shield for his oil filter. He got a sheet of perforated metal and mounted it to the oil filter with clamps using non-conductive little blocks to keep the heat from transferring to the filter. A nifty mod for any size oil filter.
Mobil 1 changed their formulation at about the same time I first tried the large 1 quart filters. Initially the oil analysis indicated a large step increase in % oxidation and it was not clear if this was due to the change in oil formulation of filter size. Subsequent oil analysis showed it to be a function of the new oil analysis and not of filter size. To make this clear no significant change in analysis, be it % ox or wear metals can be attributed to filter size for better or worse using either size filter.
In this test Mobil 1 5w-30 was changed with filter every 5000 miles on a V8 SHO. Heat was a concern because of the proximity of the filter to a exhaust down pipe. The significant concern remains that using the larger filter on engine that calls for the smaller one will void factory warranty. Using the smaller filter for an engine that calls for the larger filter is never recommended.
The big issue - at least for V8 owners - is that the wrong size oil filter will void any warranties. Say Ford in their immense charity does a cam recall or compensates those with welded or pinned cams. - No small filter, no bucks. Say you have the last V8 SHO on ESP, cam goes and you have a big filter. Would Ford use that to deny a $10,000 warranty claim? In a 1/10,000 of a NY second. Fact is don’t ever let a dealership service department see your car with the wrong size oil filter. Suffice it say if you choose to run an "unauthorized" big oil filter don’t document it well and resolve to make it a secret you take to your grave.
