AlexPeterson
Well Known Member
Today I planned a local flight. The engine was preheated, with its temperatures at about 70-80F before startup. The startup was nominal, oil pressure normal. The taxi to the departure runway is maybe 250 feet. I did the runup, and on bringing the power back down to idle I noticed the oil pressure was low. Ran the rpm back up, pressure 80+. Below is the data. Note the oil temp and oil pressure are both graphed against the left hand vertical axis. One can see the relative divergence of the pressure vs the rpm as the oil warmed up. I've never seen anything like this in 18+ years of flying it. The previous flight was 10 days ago.
Even though the oil only got to 120F, the idle pressure was way lower than normal. In fact, it was lower than I've seen it even when oil temps are above 200. Obviously, I didn't fly and instead taxied back to the hangar to scratch my head. Seems it could be a leaky relief valve, but I'm not sure. I'm going to go out again tomorrow and let it warm up longer, as well as to verify the sender accuracy. (Confession...I've long been an advocate of putting mechanical oil pressure gauges in as backups. I have one. The way the pressure was tracking so well up and down with RPM it never occurred to me that the indication might be false. So, I never looked at my mechanical gauge, which is sort of out of the way in the upper left corner of the panel. I will look at it tomorrow. )
Thoughts?
Even though the oil only got to 120F, the idle pressure was way lower than normal. In fact, it was lower than I've seen it even when oil temps are above 200. Obviously, I didn't fly and instead taxied back to the hangar to scratch my head. Seems it could be a leaky relief valve, but I'm not sure. I'm going to go out again tomorrow and let it warm up longer, as well as to verify the sender accuracy. (Confession...I've long been an advocate of putting mechanical oil pressure gauges in as backups. I have one. The way the pressure was tracking so well up and down with RPM it never occurred to me that the indication might be false. So, I never looked at my mechanical gauge, which is sort of out of the way in the upper left corner of the panel. I will look at it tomorrow. )
Thoughts?