I recently flew from colorado to southern california, then over to las cruces for the hotglass flyin. A total of around 16 hours of time was put on my 0-235 longez. On the flight from california to las cruces, I noticed lower than normal oil pressures. I normally run between 65-95psi, and even up to 100psi when the oil isn't yet hot.
On runup I saw 55-65psi. Since my normal colorado start is much cooler than the 80+ deg it was at rosamond, I attributed the oil pressure to thinner warm oil. Shortly after takeoff I noticed the oil pressure ran 35-40psi. I was very concerned and monitored it closely, almost deciding to put the plane down at the nearest field. I began thinking I had an instrument issue because the oil pressure was steady (not bleeding off), the oil temperature was steady in normal range (~180F), CHT is normal range. I continued my 2 hour leg to casa grande, oil pressure stayed steady at 35-40. I checked the oil, it a tad low, but exactly where it should have been after the 6 hour flight from CO to CA. I topped it off and continued on. The oil pressure was again 35-40psi the remainder of the trip. At las cruces, I pulled the cowls off and checked the oil pressure sender (dry as a bone). Electrical connections looked good. The engine was good and clean. I definately wasn't loosing oil. I flew the ez back home a couple days later... seeing the same oil pressure 35-40psi.
I had a couple guys tell me that 35-40 sounded great, but after getting home I confirmed lycoming says normal operating range in cruise is 60-90psi for the 0-235. So either the instrument is failing (I think this is unlikely), or something else changed.
Could the oil pressure relief valve get stuck open? I would guess I would see lower than 35-40psi if this were the case? Any other theories?
I use Aeroshell 15w50 semi synthetic.
Thanks for any ideas,
Aaron
