How much do filter bypass ranges vary from OEM?

[buickman50401]

Yesterday I was changing the oil in my wife's car and while waiting for it to drain out I was looking at filter bypass specs from various manufacturers.

I'm not sure what the OEM psi setting is on her VW, but on the different after-market filters I could find information for, the setting varied widely.

Wix - 31psi
Purolator Classic - 25-32psi (listed as range)
Fram - 20psi
K&N - 11-17psi.

I'm going to assume based on the Wix and Puro filters that OEM bypass spec is right around 30.

IF that is so, the K&N leaves me really scratching my head. Wouldn't that mean that for that application, this filter would always be running in bypass mode unless the oil was at or very near operating temp?

Either that or I'm misunderstanding the purpose/function of the bypass.

 

[ZeeOSix]

The bypass setting on the filter can vary due to differences in how restrictive the filter media is, how much debris the filter collects before choking down flow significantly, and how strong the media is (ie, how much PSID can the media take before failing).

It could also depend on the vehicle's oiling system - ie, what the max expected oil flow rate is, and what kind of oil viscosity it uses.

I'm surprised the Purolator Classic is set that high. What Purolator filter number is that one?

 

[Ken2]

Look at the number of filters listed in the WIX catalog vs. the number listed in the K&N catalog. Filter makers (WIX et al) or marketers (K&N et al) have to decide if they are going to make a filter for a particular engine that will be very close to the specs they found when they reverse engineered an OEM filter, or list an existing filter in their line that is probably close enough to OEM, or offer no filter for that engine.

 

[slalom44]

Volkswagen has traditionally had very high bypass settings on their filters. IIRC, the OEM filters are around 30 PSI. The Wix filter appears to be designed specifically for these applications, whereas the K&N filter wasn't.

Even at 30 PSI backpressure, I suspect that the bypass valve is opening up on cold starts. But it's staying open much longer with the K&N filter. Personally, I'd stay away from the K&N filter for this application.

 

[ZeeOSix]

Originally Posted By: slalom44
Volkswagen has traditionally had very high bypass settings on their filters. IIRC, the OEM filters are around 30 PSI. The Wix filter appears to be designed specifically for these applications, whereas the K&N filter wasn't.

Even at 30 PSI backpressure, I suspect that the bypass valve is opening up on cold starts. But it's staying open much longer with the K&N filter. Personally, I'd stay away from the K&N filter for this application.


The low bypass setting on the K&N might be fine if it flowed with hardly any resistance ... but only K&N would know the flow vs psid performance of that filter. This VW must have a pretty high flow oil pump if the OEM bypass setting is around 30 psi.

 

[buickman50401]

Originally Posted By: ZeeOSix
I'm surprised the Purolator Classic is set that high. What Purolator filter number is that one?


Part # L20252

LOL, just noticed this on the Purolator website:
Quote:

Metal Wars—Choose
Your Battle

Purolator oil filters have metal end caps—keeping oil clean by forcing it through the media. What do the other filters have? Cardboard. Would you let cardboard protect your engine?

In a world of metal, some things don't belong. Like cardboard end caps in an oil filter. Watch the videos.
http://www.purolatorautofilters.net/promotions/video/Pages/videos.aspx


The videos are hilarious, based on the old Battle Bots tv show. They're about 30sec.

Round 1: Castration Station (buzzsaw equipped bot) vs. The Box of Evil (cardboard box) where it just goes to down with the circular saw on the box.

Round 2: El Diablo Mucho (blowtorch equipped bot) vs. TP Killa (literally a spent roll of TP with remnants of paper still attached). Burn baby burn.

Round 3: Pyschosis (another buzzsaw bot) vs Egg Carton Convict (egg carton with a plastic knife sticking out the front). Boom/splatter go a dozen eggs.

Originally Posted By: slalom44
The OEM filters are around 30 PSI. The Wix filter appears to be designed specifically for these applications, whereas the K&N filter wasn't.

Even at 30 PSI backpressure, I suspect that the bypass valve is opening up on cold starts. But it's staying open much longer with the K&N filter. Personally, I'd stay away from the K&N filter for this application.

My thoughts exactly. The Wix is purpose built for this application. The Purolator is close enough to not matter. The K&N - full bypass till close to operating temp... and if you drive short trips, it might be full bypass a majority of the time.

 

[ZeeOSix]

Originally Posted By: buickman50401
The K&N - full bypass till close to operating temp... and if you drive short trips, it might be full bypass a majority of the time.


I guess that's the only assumption that can be made not knowing exactly what the flow restrictiveness of the K&N filter while on that car. Like I said above, it could be that the K&N flows so well that it doesn't need a high bypass pressure setting. But only K&N would know for sure.

One would think that if K&N specifies that filter for your car that it would be OK, but again I guess even the companies that deal in this stuff for a living should always be questioned on their technical prowess.