Originally Posted By: hi-miler
My mechanic friend told me that oil filters are in relief mode most of the time and are in reality a bypass filter anyway.
Is he right?
Where do I find information to prove one way or the other?
Does Amsoil have any flow numbers published showing how much better their filters flow as compared to the competition?
Is all this just a subjective discussion?
Steve
You can use the manufacturers flow/PSID numbers as a comparison ONLY. Your bypass valve setting, in conjunction with your oil pump relief setting, act as "buffers" in your otherwise immutable fluid transport mechanism. They provide "slack" in an otherwise SOLID connection of barely compressible fluids.
The flow potential or the lack of it typically has little (VERY LITTLE) meaning in 99.44% of usage.
There are exceptions.
If you have an engine that has an oil flow that isn't matched with your engine's oil demand. This would mostly be limited to pushrod engines that have our traditional distributor driven pump. They can have relief limits that are more attuned to the stress limits of the drive socket or shaft.
If you're using a higher viscosity fluid or are in extreme cold temps with a higher viscosity fluid.
If you're flat shifting @ 7,0000 rpm or otherwise transitioning pump output from one state to another at a rate faster than the fluid can physically respond due to mass/momentum.
If you have a higher volume pump that has you at the ceiling 24/7 off idle, then you're in some form of variable relief at the same time. You're also at some level of variable PSID across the filter. This is the ONLY time you can possibly be at ANY appreciable level of PSID EXCEPT due to LOADING.
Essentially, if you're not in relief (at your ceiling in pressure), and the engine is fully enveloped, YOU ARE NOT IN BYPASS. IT CANNOT OCCUR.
ANY PSID that you see below the relief ceiling of the pump is VERY LOW. It may be 2psid cold (not in pump relief) to "inches of water column" when warm. It's part of the SERIES CIRCUIT that is formed between the engine resistance IN LINE with the pump and the filter. The filter MUST be a % of the TOTAL resistance of the circuit. The engine is VASTLY ...READ: INCREDIBLY HIGHER in resistance than the filter in that circuit as viewed from the filter's perspective.
I can (and probably will) go on, but if you've got a properly sized pump and a properly spec'd oil (viscwise) and aren't in some extreme condition that will alter either in terms of realized pressures, then the issue is not an issue. If it is, it's a marginal issue that is compensated by the "slack" designed into both the pump and the filter.
Really
It's hardly the monster that some have constructed here.
I'll be happy to field some specific "Yeah- fine ..but what about ??"