I've been trying to determine what the impact of oil filter bypassing would be on engine wear and I've found an interesting old study, SAE 460133 - Oil Filtration and its Effects on Engine Wear (1946).
The study compared piston ring wear in engines with full-flow oil filtration, bypass filtration, and no filtration. The full-flow setup used the exact same "standard absorbency" filters as the bypass setup, but with 6 times more media area. In the bypass setup, 14% of the oil was filtered, and 86% bypassed, so the test results should be similar to those from an engine with a full flow oil filter that is bypassing an unusually large percentage of engine oil, or one that has a very large tear in the media.
The partial flow test resulted in a 15 to 40% increase in engine wear vs the full flow test. The difference is small despite the fact that the small partial flow filter was 5 times more heavily loaded with debris at the end of the 60 hour test (per unit area of filter media), and its efficiency would have suffered as a result.
Another study, SAE 680536 (1968), is mainly about air filtration, but they measured engine wear in real time with the radioactive tracer method, and one of the tests involved removing the oil filter after it was used to help clean up the engine between tests. The rate of piston ring wear didn't rise appreciably for almost an hour of engine operation after the filter was removed, but eventually tripled over the following few hours as the oil loaded up with particulates.
The conclusion I come to here is that the cleanliness of the oil in the sump is of primary importance, and that short-term bypassing of the oil filter is inconsequential, whether it be due to a small tear in the filter media, cold oil, high rpm, undersized filter, or low filter bypass pressure rating. Of course, it the filter is bypassing due to being clogged, filter efficiency may suffer a lot.
This question was relevant to me, since the Subaru I drive has a high flow oil pump, 102 psi pump relief, and 23 psi OEM oil filter bypass pressure rating. I've determined that pretty much any available aftermarket high efficiency filter will bypass oil regularly on this engine (up to a third of oil flow by my estimation), so there is a choice between high efficiency or full flow. I'm going to stick with a high efficiency filter regardless of the low bypass pressure rating.
The study compared piston ring wear in engines with full-flow oil filtration, bypass filtration, and no filtration. The full-flow setup used the exact same "standard absorbency" filters as the bypass setup, but with 6 times more media area. In the bypass setup, 14% of the oil was filtered, and 86% bypassed, so the test results should be similar to those from an engine with a full flow oil filter that is bypassing an unusually large percentage of engine oil, or one that has a very large tear in the media.
The partial flow test resulted in a 15 to 40% increase in engine wear vs the full flow test. The difference is small despite the fact that the small partial flow filter was 5 times more heavily loaded with debris at the end of the 60 hour test (per unit area of filter media), and its efficiency would have suffered as a result.
Another study, SAE 680536 (1968), is mainly about air filtration, but they measured engine wear in real time with the radioactive tracer method, and one of the tests involved removing the oil filter after it was used to help clean up the engine between tests. The rate of piston ring wear didn't rise appreciably for almost an hour of engine operation after the filter was removed, but eventually tripled over the following few hours as the oil loaded up with particulates.
The conclusion I come to here is that the cleanliness of the oil in the sump is of primary importance, and that short-term bypassing of the oil filter is inconsequential, whether it be due to a small tear in the filter media, cold oil, high rpm, undersized filter, or low filter bypass pressure rating. Of course, it the filter is bypassing due to being clogged, filter efficiency may suffer a lot.
This question was relevant to me, since the Subaru I drive has a high flow oil pump, 102 psi pump relief, and 23 psi OEM oil filter bypass pressure rating. I've determined that pretty much any available aftermarket high efficiency filter will bypass oil regularly on this engine (up to a third of oil flow by my estimation), so there is a choice between high efficiency or full flow. I'm going to stick with a high efficiency filter regardless of the low bypass pressure rating.
