Originally Posted By: Gary Allan
So? You've just magically produced a scenario where you have 10 PSID across the filter. Why not 20..30..40?
(sigh) ....How do I know that 100 psi applied to a given filter will produce the 9/10 split between the engine and the filter? How do you know it? You don't.
Agreed ... NOBODY knows unless they do some flow vs. pressure testing with instrumentation on an actual vehicle’s oiling system – so neither one of us can claim they know the real split. You have “guesstimated” a few times yourself. But at least the example gives an ideal of how the filter vs. engine resistance ratio to oil flow will play a part on how an oil filter
Originally Posted By: Gary Allan
My point was in regard to the test that you cited as living proof of your assertions was setup in a manner where there would always be a sizable PSID across the filter since the downstream pressure (with all the usual caveats) was always going to be around 65%. Raise or lower volume to produce a bypass event. Very easy to produce PSID ..and therefore easy to "make" a bypass event.
The key to all of these discussions is that certainly are instances when there can be enough PSID across a filter to create unwanted bypass events. This is why it’s so important that an oil filter has a bypass setting designed adequately for the application the filter is for. Subaru specifying a 23 psi bypass valve reflects just that ... because if it was set much lower (like 8-10 psi), then there are going to be WAY more bypass events going on, which could be detrimental in the long run.
The cycle filter testing IMO wasn’t so far removed for practicality. Do you think an engine could flow 1.3 gpm of cold (10 deg C) 10w-30 oil during a cold start/run use? I think it could ... and therefore, any of those tested oil filters on an engine that could produce that same flow would show the same PSID as in that bench test. Some of those PSIDs were probably up at or very close to the bypass setting. So, there really isn’t a big surprise there, as I’m sure there are thousands of oil filters in use that go into bypass mode to some degree during cold start/run use. The frequency and level of the bypass events is still dependant on the overall flow design of the oil filter AND engine’s oiling system, and how they both work together as a system.
Originally Posted By: Gary Allan
Quote:
Let’s go a step further and look at this Subaru oiling system in this case. Since the oil system specs say that it can flow 12.4 gpm at 43 psi with 176 deg F oil, this tells me right off that the engine’s flow path is not very restrictive.
No problem ..so far.. again, you default at the extreme for whatever reason you need to. I can't quite figure how this applies to too much outside of that narrow confine ..but let's go back and rehash it. I tend to agree with this, but with you it's merely a setup for something that won't necessarily flush.
Originally Posted By: Gary Allan
Quote:
Let’s say it is 4/5 ths the total system restriction, and the filter is 1/5 th.
When? I see you constructing a given pre-packaged scenario here. Try and define the difference between revealing something, and configuring something to work out the way you want it to.
You’re kind of paranoid I see.
Of course a scenario has to be “constructed” to get point across. You do it all the time too. I don’t think it’s that unrealistic. It doesn’t have to be 100% realistic to describe the physics.
Originally Posted By: Gary Allan
Quote:
So the max flow and hence max pressure drops throughout the system will occur when the oil pump is in relief mode – 85 psi in this case.
How do you figure? In relief mode:
A: You have less than max flow
B: You DO have max pressure applied
C: You can have 85lb and be in relief at virtually NO VOLUME to the engine (startup and until the fluid gets moving).
You haven't qualified the conditions well enough. You've just stated that something is so without thinking it out too far.
OK, let me explain. Please realize that anytime the oil pump is in relief mode that this point is where the max flow to the filter/engine circuit occurs – depending on the oil viscosity of course. This is kind of tricky to comprehend (and describe too), so stay with me.
Your item A) above. Yes, when the oil pump is in relief mode “you have less than max flow” ... BUT really only less than the possible max the pump could have produced IF it wasn’t in relief mode. Since it IS in relief mode, then the oil volume that actually goes through the filter/engine flow path IS the maximum you can ever achieve (with xyz oil viscosity of course) because this is the maximum pressure that can ever be put on the system. With higher pressure you get more flow. So, max flow ALWAYS happens when the oil pump is putting out max pressure at its relief setting. Keep in mind that the oil pump COULD produce more pressure and flow if it could go above the relief point.
Your item B) above. Yes, agreed. And just as I explained above, this also correlates to having the max possible flow going to the filter/engine. The pump DOES put out more flow, but the excess volume gets spit back to the sump, and the volume going to the filter/engine remains constant at the pumps relief pressure point.
Your item C) above. Same principle. In the case you site in item C), you are still at the max flow that is POSSIBLE under those conditions. In other words, you can NOT flow more than what will flow with 85 psi trying to push the oil through the flow path. We both know that as the oil starts warming up, the then the actual flow VOLUME will also increase. Imagine the oil pump is in relief mode at 85 psi instantly from cold start to full oil temp. Of course the flow volume will be a lot smaller at cold start then at full operating temperature ... BUT, during the whole warm-up period, the MAX POSSIBLE flow to the filter/engine was always maxed out because the oil supply pressure was always at the max possible of 85 psi. Look at it from the supply pressure point just downstream of the relief valve. Look at the pressure and flow volume at that point, not at the point between the oil pump and relief valve.
Originally Posted By: Gary Allan
Maximum possible flow will go to the engine (whatever that may be). Maximum pressure is applied (and can be exceeded). The difference between flow at 85lb in relief and 85lb out of relief will be the difference between the flow seen by the engine vs. the total flow output of the pump.
Well, IMO ... “technically”, the flow coming out of the pump right at the 85 psi relief point is just on the verge of splitting between the filter/engine and sump. This is a bad pressure to talk about flow split because the spit is ill defined right at the relief setting. We both know and could say that if the pump outlet was say between 1 and 80 psi then there should be no slit, and all the pump’s output volume goes to the filter/engine. But if the pump’s output pressure hit 85 psi, and the pump’s RPM was then still increasing at this point, (remember that a PD pump’s RPM is key here), then the oil pump WILL put out more volume, but any volume in excess of what can be pushed through at 85 psi to the filter/engine will be spit out the relief valve to the sump.
Originally Posted By: Gary Allan
The difference in pressure (drop, if you must) across the engine (due to the flow passing through it) and the pressure applied will determine the pressure differential across the filter. Once the flow is unified (a single flow) the engine will drop (if you insist) more pressure due to more flow going through it (buffoons will admit this) ..YET THE APPLIED PRESSURE WILL REMAIN THE SAME @ 85LB OUT OF RELIEF.
The differential across the filter will evaporate to next to nothing.
A CHILD CAN REASON THIS (at this point, anyway).
None of the above has once challenged the flow limitations of the filter. You seem to obsess on this aspect of the filter that is so rare ..all for what?
Now, now ... I’m sure a child would actually have no idea whatsoever what any of this discussion means. I haven’t seen but a few comments made from other members here with regards to our detailed discussions, so apparently either everyone else besides you and me fully understand it, or else they don’t want to even get involved because they don’t understand it.
I think you’ve mis-read or misinterpreted (“read between the lines”) some things I’ve tired to say in some of these discussions. All of my discussions and examples are assumed to be after the engine has started and the oil pressure has come up and has filled every nook and cranny of the oiling system with flowing oil – ie, “steady oil flow” conditions. I really don’t care about the instantaneous physics going on here – ie, starting a cold engine with a dry filter and engine galleys not filled up.
You think that “the difference across the filter will evaporate to next to nothing”. Well, it really DEPENDS on a number of things. As we have hashed over more than once on this, the engine’s oil flow path resistance will dominate in determining exactly what flow rate goes through the filter/engine flow path. No agreement there ... and YES, the engine flow path WILL be more restrictive than the oil filter ... BUT, just how much more? This is the KEY to this whole discussion. Not every engine will have the same flow resistance. The Subaru in question obviously seems to have an oiling system that is quite a bit less restrictive than most cars on the road, and this DOES play a part on how the oil filter must be designed for an engine application like this. That has been my main focus in these discussions all along. Yeah, it might be it a so called “rare case”, so why always try to divert from this and always assume it’s like all the other cars on the road? – I’m not claiming that EVERY oil filter might have some flow/PSID/bypass issue.
But in a “rare case” like this, the flow limitations of the filter could certainly be “challenged” by the application – that specifically being that using a filter with the wrong bypass setting on an engine like the Subaru could certainly cause excessive bypass events, which could lead to other problems as one member posted about (debris in the turbo oil line screen filter that eventually chokes oil to the turbo and smokes it.).
Originally Posted By: Gary Allan
That's enough for now. Yes, if he's going to operate @ 5000 rpm ..he'll need a higher bypass rated filter just as much as he does while he's in relief (many ..many..many more times) at cold start and through the warm up process ...and most of it from idle through the point of dropping below 85lb of pressure regardless of the volume output of the pump for a goooooooood long way up to peak volume capability.
***? ... I can’t believe it, after all of that. You’ve just confirmed what I’ve been claiming (and have said) all along! It’s a miracle!
