How bad is lower bypass relief pressure?

[sipman]

I've got the Bosch D3421 filter designed for my car (1983 VW Rabbit GTI) and I've got a bunch of D3422 filters for a former car of mine. The 3421's relief valve psi is 25-25, while the 3422 is 12-15psi.
Should I just get rid of these 3422's considering I'd probably be in bypass a large amount of time? Would you consider using them, but doing very short intervals?

 

[ripcord]

Why do you think you'll be in bypass a lot of the time? Bypass only happens when the pressure on the pump side exceeds the pressure at the filter outlet side by the relief valve rating. If you don't run crazy thick oil in cold temperatures and rev the engine hard before the engine warms up or fail to change the filter before it loads up with crud, then the filter will rarely bypass.

I'd use them.

 

[Passport1]

How bad is lower bypass relief pressure?​

Tee'd up for an odiferious quip but I won't. BITOG mods might not approve.

 

[oil pan 4]

It's not bad it just is what it is.
Unless you're in the cold or down south running 20w-50 all year it likely won't bypass.
If it does bypass it will only be for a few minutes and only some of the oil.

 

[twX]

That's a large filter on an engine that probably doesn't have a really high oil flow rate. I'd expect the initial dP across the media to be in the range of 2-5 psi. As a rule of thumb, the bypass setting should be at least 3 times the initial dP, to ensure a good dirt loading capacity, so a 15 psi bypass should be fine.

The lower bypass setting will just mean that the filter will start bypassing when it is slightly less clogged, and it might bypass briefly on cold starts even when the oil is not extremely cold. Change the filter regularly and there will be minimal bypassing.

The advantage of the lower bypass setting is that the engine's oil pressure won't drop as much if the filter clogs. Low oil pressure is generally more dangerous for an engine than abrasive wear. If this engine produces over 80 psi at high rpm, the 25 psi bypass setting should be fine. If normal oil pressure is more like 60 psi, a filter with a 12-15 psi bypass will actually be safer for the engine IMO.