What is the difference at cold idle? Keep in mind that when someone says they “hear” a significant difference - this is occurring typically right after startup, after an oil change…
Maybe it's because the oil filter's ADBV isn't doing its job and allowing the oiling system galleries to drain out, which can cause engine noise for a short time after a cold start-up.
I want to say a current Hemi has ~7 psi at idle, hot. The difference in 1 or 2 psi is big! 15% of the overall flow!
Is ~7 psi within the normal operating temperature for that engine? Sounds like a variable displacement pump, or a pump that is designed to regulate to a set oil pressure vs engine RPM. These are still PD oil pumps, but the pump is regulating by computer control the actual pressure with some kind of oil pressure sensor, then it still wouldn't matter what the restriction of the filter is because if the filter had 1 or 2 psi more of flow delta-p (restriction), then the computer would still try to maintain the set-point oil pressure at the feedback sensor.
The water filter in the house is installed at the tap, after the primary restriction (pipe size has already been reduced, and so the result is very drastic).
In most engines, you are still on the “Primary” side. But where in my 90s engine, the passage has about 2.5x the volume of the secondary feeds, some of these new engines aren’t sporting near as much differential either.
It doesn't matter where the filter is located, because in a hydraulic system that is feed/supplied by a constant pressure source (like the plumbing system in your house), if the filter becomes flow restrictive (ie, clogged up), the flow volume will decrease. But in an engine oiling system with a non-variable PD oil pump, the system is never in a fixed pressure feed/supplied mode until the PD is in pressure relief. The only way an engine oiling system could make the PD pump hit pressure relief at idle or low RPM is if the filter is basically completely clogged and the filter is in bypass with a very small bypass opening. Highly doubt that's happening in any situation where there is a new oil filter installed.
In an engine with a variable flow/variable pressure oil pump system, the specific oiling system needs to be totally understood before any accuate assertations can be concluded on what's going on, and what's causing what. Does the factory shop manual outline the details of how the variable oil pump is controlled? Does it actually use the oil pressure sensor as feedback to control the pump?
I might say the noise difference was attributable to a thicker viscosity of oil, as it’s new - but oxidative thickening would likely prove otherwise. I might have told you that the additive differences in Red Line Oil eliminate the so-called Hemi tick - but it comes back after 2-3K with a Mopar filter - while it remains gone for the 7500 mile intervals with the Fram, using the same oil…
So somehow, the filter is making the difference… another primary difference between them is that the capacity is much higher on the Fram as well, meaning the differential pressure is not only 50% higher to start, it increases to a significantly higher percentage improvement over time!
The holding capacity and how the filter performs in flow performance (the "flow vs delta-p" curve) are not necessarily related. The Fram Ultra for instance has a very high holding capacity, yet it flows very well even as it gets loaded up with debris. Maybe that Hemi oil filter loads up really fast and isn't really good for anything above a 5K of use.
I have seen first hand, that with many of these new pumps, it may see 7 psi at idle (650 RPM), and by 900 RPM, it will ramp to 40-45 psi… I honestly think they have dialed them down to a point where flow at idle is a significant issue…
Yeah, I'd say if a variable flow PD oil pump is only supplying 7 psi at hot idle, that seems like the engineers are cutting it down too far IMO. Where is the oil pressure sensor located on this engine? I'd guess it's located after the oil filter like most engines are.
But the fact still remains that if the pump is not in relief at that low oil pressure condition, the oil flow volume will not change depending on what oil filter is used. That is the whole key to an oiling system that uses a PD oil pump ... which every engine has used as long as engines have been around.
