How does a 2-step pressure relief oil pump work?

[GravelRoad]

Never heard of one. Only heard of a single psi relief valve.

In my 2016 Subaru Outback 2.5L Shop Manual (in pdf form), under General Description Specifications of the oil pump, it reads the following.

Oil Pump:
Relief valve working pressure
(2-step relief)
1st opening pressure 21.7 psi
Main opening pressure 82.6 psi

Found no other details in the manual.

Any facts, guesses on how an oil pump 2-step pressure relief works/operates?

 

[OneEyeJack]

Take a second look. You've got me confused.

 

[Jetronic]

the first would be a very small opening, which limits the oil pressure at low rpm and high viscosity oil (cold operation). the main pressure relie opens much bigger.

 

[meep]

V6 Pentastar does something similar, two different output passages on the pump to reduce parasitic loads.

 

[Srt20]

Originally Posted By: meep
V6 Pentastar does something similar, two different output passages on the pump to reduce parasitic loads.


Funny this comes up today.

Yesterday I was watching my oil psi gauge in my pentastar.
I know that the psi is higher when the oil is below 165*F. After that the psi drops close to half.
But also at approx 3500 rpm the oil psi kicks back up to almost double again. But doesn't necessarily drop back down at 3500 rpm on the decel.

But what I discovered yesterday was at around 1200ish rpm the oil psi increases again even with warm oil. Meaning I could not get the oil psi gauge to read below 36psi. At around 1400ish rpm on 170*ish oil the gauge was 36psi. As the engine dropped even lower in rpm, the oil psi kicked up into the 40's psi again.

I didn't have time to play around and get a good read on what exactly was going on at each rpm, and I was in town with my kids. But I will figure it out soon on some back roads.

So while I thought the pentastar oil pump was just a 2 stage or 2 speed oil pump, it clear its more than just that. Pretty cool.


btw, I use 0w-20 PP just for reference.