Different bypass valve pressures

[westwind999]

I was recently comparing the same size filters for the same vehicle and noticed that some manufacturers use different bypass valve pressures. Purolator seemed to be higher that Wix. Some companies don't provide a lot of data. Should I be concerned about the pressure? Would lower or higher be better? I imagine a lower pressure would prevent the media from bursting but might dump unfiltered oil through the engine.

Why wouldn't the filter companies need to use the same bypass valve pressures to maintain new car warranties?

Thanks

 

[wcbcruzer]

I doubt you'd ever really use the bypass feature of the oil fiter. I'm pretty sure your car's bypass is much lower than the filter's.

 

[94MaxGXE]

wcbcruzer, Thanks for the post, but you have no idea what you are talking about.
The engines oil system high presure bypass is probably somewhere around 65 t 85 psi. The oil filter rating of 9 to 11 psi is the differential presure of the input to the output of the filter.
That is, if the flow is restricted by the paper elemint more the 10psi+-1, the filters bypass opens and allows full flow.
When the oil is cold, little oil can flow through the filter paper. The oil filter bypass will open to allow all oil to flow. (Thats why these are FULL FLOW filters)

As the oil warms and thins, more can flow through the filter element. Does it ever stay closed ? I bet even at full temp, you crack a WOT and that filter is in bypass.

I would bet that MY filter has the bypass spring pushed all the way back for the first 20 mim that I drive it. I just start it and gun it......company car only........

 

[Ken2]

For clarity, the "bypass" connected to the car's oil pump can be called the oil pressure control valve.

The bypass in the oil filter, or the oil filter mount of the engine, can have its pressure set at a pressure that is safe with the filter media and media assembly the filter maker chooses to use. Generally, the engine maker does not publish their oil filter spec...the filter makers reverse engineer an original equipment filter, pick one out of their product line that is probably close enough, and recommend that one.

As 94 says, the filter bypass should always be referred to as seeing differential pressure...a 10 psi bypass can have 100 psi entering, 91 psi exiting the filter, and never bypass. (Actually, they are not at all precise, and we don't know if the stated pressure is when they begin to open, or are fully open, or exactly what they represent.)

 

[Gary Allan]

Quote:
I was recently comparing the same size filters for the same vehicle and noticed that some manufacturers use different bypass valve pressures. Purolator seemed to be higher that Wix. Some companies don't provide a lot of data. Should I be concerned about the pressure? Would lower or higher be better? I imagine a lower pressure would prevent the media from bursting but might dump unfiltered oil through the engine.


The difference between one spec'd filter and the other identical spec'd filter is the difference in media tolerances to differential pressure (as you sorta eluded to).

Quote:
Why wouldn't the filter companies need to use the same bypass valve pressures to maintain new car warranties?


Where specific bypass valve ratings are called for, most filter man's produce a separate number for that application.

Bypass valves are in highest potential for use at cold start. It breaks down to two conditions. Where the galleries are empty and there's no "back pressure ..and when the pump is in relief. It has little to do with the resistance of the filter, per se~. That is, the filter doesn't "magically" materially change ..but the pressure differential is different with the pump in relief. Pump not in relief, the filter has a very low apparent resistance. All the oil passes through the engine ..and the engine is BY "SO WAY HIGH OVER THE TOP" FAR the BIGGEST GALACTIC OCEANIC TITANIC restrictive thing in the fluid circuit ..that the filter is CHUMP CHANGE.

Now open the relief, and then the physics changes. At that point the filter can appear as high as the bypass valve setting.

 

[RWEST]

Quote:
I just start it and gun it......company car only........

 

[westwind999]

Thanks for the feedback.

So, say my car had an oil pressure of 15 PSI at idle when it's warm and I had a filter with a 15 PSI bypass pressure. If the filter was close to clogged maybe there would be enough back pressure that no oil could get through? Maybe the lack of flow would mean that the oil pump would build more pressure until the oil went through one or the other?

 

[westwind999]

I just thought of something else. Which side of the filter is the oil pressure light/gage? If the filter was blocked and the bypass valve closed wouldn't the light come on?

 

[Steve S]

Originally Posted By: westwind999
I just thought of something else. Which side of the filter is the oil pressure light/gage? If the filter was blocked and the bypass valve closed wouldn't the light come on?
If the filter bypass was blocked there may be a good chance the filter element would be the weak link in that chain.

 

[widman]

The oil pressure is measured between the filter and the bearings (normally). Some cars also have their own bypass valves (mine has one at 10 psi differential) so it does not matter what filter I put on it as long as it is over 10 psi differential.
I think a lot of filters are in the bypass or dry run mode on startup and would not put a filter on with a higher bypass rating than that called for originally.
When it says 8-11 psi, it means you should start getting some flow through it at 8 psi and it should be fully open at 11 psi.
Why are some of those valves bigger than others? That is another question.

 

[Gary Allan]

Originally Posted By: westwind999
Thanks for the feedback.

So, say my car had an oil pressure of 15 PSI at idle when it's warm and I had a filter with a 15 PSI bypass pressure. If the filter was close to clogged maybe there would be enough back pressure that no oil could get through? Maybe the lack of flow would mean that the oil pump would build more pressure until the oil went through one or the other?


Your engine is only DEVELOPING 15psi at idle due to the viscosity of the oil at that temp and the flow of the oil pump at that speed.

This is not an easy concept for many. Pressure is "developed" ..it's not "supplied". Flow is supplied and the pressure is a result. That's as long as the pump is not in relief.

How much oil is passed through a 2" pipe @ 5gpm?
How much oil is passed through a 0.25" pipe @ 5gpm?

A: 5gpm. The difference is the velocity and the pressure developed. As long as the pump producing the flow wasn't in relief and pump losses not excessive ..the difference is velocity and pressure developed.

An extreme example ..but that's the idea.

It's not like a garden hose. It's not like a water faucet. It's not like the wall electrical outlet. Those are applied pressures that result in varied flows depending on the resistance/restrictions that the flow encounters.


Now once the pump is in relief, then you DO have a supplied pressure pushing into a restriction/resistance. The filter is limited in what it presents to the flow (in terms of resistance) by the bypass valve setting.

When the pump is not in relief, then whatever resistance the filter presents is translated into a pressure elevation ..or increased "back pressure" in addition to the "back pressure" that the engine produces at the given flow rate.

Out of the relief state, the filter is an EXTREMELY LOW restriction compared to the ENGINE. They both have to add up to the total developed pressure. BIG (engine) RESTRICTION? very small apparent filter restriction