Just returned
from about 2500 nm trip. Engine ran great, including flying over the
Rockies west of
Denver where I was
briefly at about 14,000 ft with density altitude of 16,500, and still had
some throttle to go. Generally cruising at 165 KTAS, 9.2 – 9.5 gph, about
5600 rpm. Not bad for a 4-place airplane.
OK, now for some
technical stuff. You
may recall I converted my 20B over from pan oil injection to using
premix.
The main issue is
the amount of 2-cycle oil that is ending up in the oil pan. When
mixing 1 oz/gal I found the pan oil level had gone up by about 1 ½
quarts (from 6 ½ to 8) in about 15 hours of flying; and my nice clear-amber
15-50 synthetic had become the dark blue-black color of the SuperTech
2-cycle oil. Doing the math suggests that about 1/3 of the pre-mix oil is
ending up in the pan. That seems way out of line, and although a
suspect it is not harmful to the engine, I don't think it the best lube for
the re-drive. I changed the oil and reduced the amount of pre-mix to ¾
oz per gallon. I'll be surprised if there isn't still some 2-cycle oil
going into the pan.
So. . ;
suggestions? Use different brand 2-cycle? Further reduce pre-mix
amount?
I'm wondering if
the fact that my cruise coolant temp is now running around 150F would result
in more of the pre-mix to condense out than if it was running at maybe
180F.
Another thing I
notice is a small amount of fuel is coming out of the fuel vent. The
only explanation I can come up with is foaming/bubbles forming in the return
line after the pressure regulator. This goes into the 3-gallon sump
tank and up the ¼" vent line. This may have been occurring previously,
and the fuel evaporated as it went back along the surface; but now the blue
2-cycle oil is left behind to be quite visible at the back of the cowl; but
I suspect the pre-mix is exacerbating the foaming.
I notice the
plugs have less carbon than before, and the inside of the exhaust exit is
now very light grey.
Al