Originally Posted By: Ken2
Lots of bad info here, as well as overly complicated info.
All that matters is the difference in pressure from the inlet side of the filter to the outlet side. That's all. That's all the relief valve can measure, and that's all it reacts to. (Ditto for GM's oil filter relief valve built into the oil filter mount instead of inside the filter assembly.)
True ... but as mentioned there are MANY factors that determine exactly what the PSID is across the media / bypass valve. It is more complicated when you realize how many factors there are.
Originally Posted By: Ken2
If the pressure drop (differential pressure) across the filter is up to the relief valve's set point, the relief valve will open. When the pressure drop lessens, the relief valve closes. These relief valves are simple and cheap, so don't expect accurate results. The pressure drop through the engine has no relationship to the filter, nor does the oil pressure. Thicker oil has more drop through the filter, so that opens the relief valve, as does dirty media. Increased oil flow will increase the pressure drop, other things remaining equal, and if the oil isn't thin enough will cause the relief valve to open.
Comment about your text in red above. For sure the pressure drop is related to the filter's design and to the oil pressure. If the filter is designed to be restrictive to flow the bypass valve will open easier & more often than if it was a free flowing filter. The oil pressure is what causes the oil volume to flow ... so more oil pressure will increase oil flow which in turn will increase PSID. Like I said, there are many factors involved.
Originally Posted By: Ken2
Let's call the valve at the oil pump a pressure control valve just so we have terminology that is less confusing. This means nothing to the oil filter relief valve, anyway.
True ... I've mentioned that many times. Some people don't believe this, but they are "off base" and don't really understand the total oiling system dynamics.
Originally Posted By: Ken2
What determines flow through a filter is the number of holes in the filter media, not the total area of the media. If new-tech media has the same number of holes of the right size as old-tech media, it'll filter the same and flow the same.
Technically both are a factor. It's the combination of the media used, and the total area of the media.