Prop Cycle rpm has changed
The rpm at which my Hartzell prop cycles during runup has recently changed. It used to always cycle easily at 1600 rpmís, 1400 rpmís, or even lower. I always wait until oil temp is approx. 100F before cycling the prop.
Governor is M/T which I bought in April 2006 (when they were still called Jihostroj by Vanís). Engine is IO360-A1B, 200 hp angle valve. The airplane was first flown in 2013 and has over 280 hours on it, now.
I originally had a single 7 cell oil cooler mounted behind #4. In July 2019, around 220 hours, I added another 6 cell cooler behind #3 to improve oil cooling (which works very well).
I had always run Shell 100W Plus and a pint of camguard at oil change. Engine has chrome cylinders so uses oil at a higher rate than steel cylinders. However, after installing the additional oil cooler, I started using Philips 20W50, no camguard. Oil consumption became a little less. Oil was added as needed, around Ĺ quart at a time.
I flew nearly 40 hours (with one oil change, Philips 20W50, at 25 hours) before the rpm change occurred.
At about 260 hours, unexpectedly, the prop wouldnít cycle until runup to about 2000 rpm.
It still works as expected in flight, maintaining rpm as before.
Iím aware recommended but not required 72 months recommended TBO.
But still, the change was sudden.
Could the Philips reduced oil viscosity (at the ≈ 100į runup temp) cause this? More total volume of oil due to the added cooler?
Any ideas welcome.
Daryle L. Grounds
McKinney, TX Based @ T31
RV-7, N33DG, IO-360-A1B, Hartzell C/S, Flying since 12/15/12; Swick TCraft under construction