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