This summer I was wondering too. I was running synthetic for some time. I had some funky readings (low) coming from my VDO gauge (in Phoenix heat). I suspected to find fine shavings in my pan. Oil analysis turned out ok at an oil change. I kept an eye on the pressure and over time I noticed a rap on the gauge would set it back to normal pressures (+65 psi at speed, an 16-20 at idle).
Lesson learned, these gauges are crap.
Mine is roughly 6 yrs old and failed. It was my gauge slowly failing.
?
Sean G
________________________________
From: Tom <grabaman@...>
To: subaruvanagon@...
Sent: Monday, December 10, 2012 4:21 PM
Subject: [subaruvanagon] Oil Pressure Findings
?
For the first time in 50k on my conversion, I used a non-subaru oil filter (Mobil 1 filter). My oil pressure readings were lower than normal - especially at higher rpms where I saw less than 10 psi/1000 rpms at hot, but not summertime hot, operating conditions. Spec is 43 psi at 5000 rpms hot and I was near that number.
With OEM filters, crossing Nevada in 100 degree temps pulling passes in 3rd gear at 4800 rpms, I've never seen pressures less than 10 psi/1000 rpms. So I was concerned that the 2.2 was getting tired. And I started questioning my VDO pressure guage sending unit.
I pulled the M1 filter, put an OEM filter on, and oil pressure returned to "normal" (same 10/30 castrol syntec/edge in the engine).
There is a fair amount of banter out there about the oil filter bypass pressure (not to be confused with the bypass valve on the oil pump which is set to 71 psi): OEM is around 24 psi ... most after market filters seem to be in the 15 psi range. I understand this as a pressure differential across the filter - if it gets above the threshold, the oil bypasses the filter so flow to the engine, albeit unfiltered or partially filtered, continues.
I'm still a little confused how an oil filter with different bypass pressures can affect pressure at the engine, and maybe I had a bad Mobil 1 filter, but I'm happy my oil pressure is ok with an OEM filter.
Nothing but dealer oil filters for me from here on out.
YMMV.
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