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