Mistake to use filter w/ lower bypass than OEM?

[edhackett]

Answering for the OP again, assuming that he is relatively new to Subaru. He can feel free to correct me.

Subaru changed the exhaust manifolds on the turbo engines in 2005-2006. The diameter of the filters in use at the time were too close to the headers, causing heat problems. Subaru went to a smaller diameter filter to solve the problem. The 14460 is the old, larger diameter and shouldn't be used.

I suspect the higher by-pass is for the reason that Gary mentioned. I suspect my WRX was in pump by-pass for up to 5 miles on a cold morning. That observation being based on the pressure reaching a plateau at 100 psi and only dropping under that once there was some heat in the oil.

Ed

 

[LoneRanger]

I don't understand what it means that the pump is in relief. I don't know much about oil pumps in cars. I thought they were just a mechanically driven pump that pumped continuously the entire time the engine was running, varying with the engine rpm.

I did try briefly the larger 51356 Wix on my car. Same outter diameter, just one inch longer. Exhaust heat shield clearance was a little close at the end of the filter, plus it seemed like my engine felt different not as smooth and that freaked me out so I took it off immediately and put another 51365 on.

Most of this is going over my thick head. I probably need to stick a Subaru OEM "Fram" on it and just forget about it.

 

[Jim Allen]

The only significant difference I see is the bypass setting. I get it.

The oil filter with a high setting might cause the oil pressure relief valve to activate more with a viscous oil but I think the engine would still be the more restrictive part of the system.

A lower filter bypass might allow the engine to get oil faster on a cold start, but a lot of that would depend on the oil. I think, then, that a high bypass setting is probably a real safe thing with today's lighter oils.

I suppose you could get into trouble if there was a high filter bypass and a high oil pump relief (or a restrictive one), combined with a highly viscous oil.

You're about to become the new "Filter Guy." Gosh, I miss him!

 

[SuperBusa]

Originally Posted By: Gary Allan
The images were to show you that I'm not talking out my [censored]

Not for you to read them for out of context dissection

The one with the spread was a relief event in progress. The top gauge had not peaked yet.

Idle hot on this thing was about (from memory)
24/26 20w-50
15/17 15w-40
12/11 xw-30
5/5.x xw-20
Close to zero/zero with 0w-10


Well, shame on me I guess for not first specifically asking you WTH conditions the gauges were reading - LOL. Since you had no particular explanation of what was going on at the time the photos were taken, I had to make some assumptions.

 

[SuperBusa]

Originally Posted By: Jim Allen
So, the bypass valve setting on the filter is as much an indicator of the filter's ability to withstand a pressure difference (i.e. continue to filter) as it is anything to do with the engine.


Yes, I've eluded to that very logic a few times now in these discussions. Someplace I've said the filter's by-pass pressure is based on the filter's design ... it depends on what the filter's flow vs. PSID characteristics are, and also how much maximum delta P the element can withstand. The filter's by-pass is it's own independent protection system to ensure it doesn't have a filter element failure from too much delta P across it ... be it trying to cram too much viscous oil through it and/or the filter element becoming to loaded up with contamination.

 

[SuperBusa]

Originally Posted By: LoneRanger
I don't understand what it means that the pump is in relief. I don't know much about oil pumps in cars. I thought they were just a mechanically driven pump that pumped continuously the entire time the engine was running, varying with the engine rpm.


Automotive oiling system in a nutshell.

The oil pumps in cars are "positive displacement" type of pumps. This means that if they take in X amount of volume on their intake port, then they also spit out that same X amount of volume on their output port. So, ideally they will put out more and more volume as the engine RPM increases; in basically a linear fashion.

Now imagine that that there is a fixed flow resistance connected to the output of the oil pump ... this would be the (oil filter + the engine's oil system) in a serial flow path.

If you try to increase the flow rate of a fluid through a fixed resistance then the pressure will have to increase at the pump outlet accordingly. If there was no oil pump relief valve, the pump would still try to force it's positive displacement through the fixed resistance, and it's possible the needed pressure could rise sky high to do so.

So, there is a pressure relief check valve placed between the oil pump's outlet port and the oil filter. When the pressure at the check valve becomes higher than the check valve is set to, some of the oil flow is diverted straight back into the oil pan.

The oil pump's relieve valve is designed to protect the engine's oil system from over pressure.

The oil filter's by-pass valve is designed to protect the oil filter.

The engine's oil pump relief valve and the oil filter's by-pass valve work independently.

 

[SuperBusa]

Originally Posted By: Jim Allen

The oil filter with a high setting might cause the oil pressure relief valve to activate more with a viscous oil but I think the engine would still be the more restrictive part of the system.


That's a possible scenario, but IMO I think it's also possible for an oil filter to go into bypass before the oil pump pressure relief does if the filter is blocked or is very restrictive for some reason and also has a pretty low bypass setting.

Originally Posted By: Jim Allen
A lower filter bypass might allow the engine to get oil faster on a cold start, but a lot of that would depend on the oil. I think, then, that a high bypass setting is probably a real safe thing with today's lighter oils.

I suppose you could get into trouble if there was a high filter bypass and a high oil pump relief (or a restrictive one), combined with a highly viscous oil.


To me, when I see a filter with a high bypass valve setting it means a few things to me:

1) The filter maybe more restrictive to flow, so the bypass is set higher to prevent the filter from unnecessarily going into bypass mode. The worst thing you can have is a very restrictive filter with a low bypass setting.

2) The filter element can take higher delta P across it.

If a filter flows very well, and had a higher bypass setting then it will probably never go into bypass unless it's highly contaminated and blocked significantly.

This is why I'd like to know for instance what the flowrate characteristics are for the PureOne. It has a bypass set higher than most. Is it to accommodate it's possibly higher flow resistance, or to accommodate the higher oil flows due to higher system pressure of the European cars? - that is kind of what Purolator engineering correspondence eluded to.