One fault of the rotary is that the combustion chamber is very cold and very large, compaired to a piston engine. So in NA form it is free of detonation in most cases, and runs well on dismally low octane fuel.
Under temp on the coolant and oil makes it worse, so more of the fuel near the apex seals condenses out and will not burn, and thus the reputation for high HC (unburned hydrocarbons).
So coolant at 180 or 185 and oil at 160 or more is the cure for some of the problem.
Multiweight oil has base stocks at the lower number (15) W 50 so you have lite oil with a bunch of ploymers to make it act like 50 weight oil at full temperature. That combination is of little value in an airplane. Mistral had problems with their oil temps running away. They were using multi weight airplane oil that foams like crazy. They changed to straight weight car oil and temps improved. They took the bug screen off of the pickup, and got more improvement. They built their own oil pump housing and pickup, and fed the pump from both ends and got further improvement.
The rotary foams oil by way of spraying oil into the spinning rotors to cool them. Polymers in that oil are a disaster. A straight weight synthetic of 30 to 40 weight would be better. If foaming is still a problem go to a racing synthetic to get the extra anti-foaming package. So the oil scrapers can stay on the irons and not ride up on the thick oil and collect fuel and 2 cycle oil to force back into the crank case. My 40 weight RedLine synthetic racing oil is plenty thick enough for 9,600 RPM on a scalding hot day. It also has very low drag at any temperature, so it gives you free HP and no need to change oil for cold weather starting.
The 3/4 ounce or one ounce per gallon of synthetic 2 cycle oil is for all out racing.
The stock oil injection consumes microscopic amounts of oil. 1/2 ounce of synthetic or 3/4 ounce of dino based 2 cycle would be more than adequate.
Plug color and tail pipe color is good if you are using low lead avgas. Car gas make differing colors or more likely no color that can help with tuning. So sad.
Lowering the oil in the fuel will help a bit if the fuel is foaming a bit. If car gas gets a bit of heat in it and high altitude it can boil now and then.
Lynn E. Hanover
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