my previous flights the plane has been coated with a nice golden brown coat of oil. the engine is a 46 os fxi. previous flights have been at reduced power. my last flight i did some full speed flying trying out some loops and rolls. after i got the plane on the ground i noticed the oil coat on the plane was a grey to black looking oil. does the oil burn more at high speed flight. or did something in the engine go bad?

New engine? Chances are it is engine wear from your engine still being broke in. It'll come out of it once the break-in process is finished. My engine did this after the first few flights as well.

If it's an already well broke-in engine, then you could have a problem.

yes it is a new engine has about 9 flights on it. but yesterday was the first time it has been run at high speed for any length of time.

If your exhaust is tight, I'd pull the head off. The OS 46 FX is known to have a cylinder peeling problem. OS denies the problem, but search here on RCU, and you will find many problems.

Most likely you had the engine set too lean. An engine with a too lean setting will run richer when throttled back slightly, in fact it is a well known technique to experienced flyiers that if they get up with a lean setting to throttle back until they can land and readjust the needle. Most flyiers can't needle engines very well, as most set for maximum rpm on the ground and are cooking their engines in the air. When you take off, the prop unloads in the air (the prop is partly stalled on the ground). With the higher rpm in the air, the engine needs slightly more fuel, an leans out slightly.

The best way to set the engine on the ground is to run it up to full throttle, then quickly pinch and release the fuel line. The engine should pick up rpm with the quick pinch test. If it sags, then you are already too lean. This assumes the following, that the tank is located correctly, muffler pressure is attached to the tank, and that the engine bolts are all snug. Also be aware that you may be running too much load on the engine - either too high a pitch or diameter or both. For a newer engine stay at the lower end of recommended prop sizes until you have run at least a gallon of fuel. Alway use the pinch test at the start of each day.

Another thing that can also leave a black streak is if the muffler is loose. When two aluminum part rub, the particles are so small that it looks black in the oil. Which if you are runing too lean comes from your piston.

Deadeye briefly touched on something that you should look at first... Tighten the muffler. Even if it SEEMS tight, Vibrations will wear the metal at the connection and will result in a black residue.

Also be sure to check the joint between the front and rear halves of the muffler. The muffler might be tight to the engine, but the threaded rod holding the muffler together might be loose, causing the black gunk (as metioned above, bits of metal)

thanks i wish i knew more about engines. i also noticed when running it seems that theres oil comming out of the nipple base that the exhaust line hooks up to. my trainer said that there was a split in the line so we cut it. but there was still oil comming from the base of that nipple. dont know if thats normal or not or has anything to do with my problem.

That would contribute, yes. You should immetidaly tighten down that pressure nipple. Better yet, remove it, clean it and the muffler with solvent to get rid of all the oil, and locktite it back in place.

If you leave it loose, the vibration will eventually strip out the threads, and the pressure tap will fall out. In the mean time, it is slowly wearing, and creating metal particles in your exhaust.

Black colored oil is never a good thing, you should always figure out where it's coming from and do something to make it stop.

I had black exhaust residue coming from a new OS 40. Tightening the muffler did not help. Eventually I took the muffler apart, cleaned the oil off, and put hi-temp silicon sealant around the joint between the front and back halves of the muffler. I reassembled the muffler and let the silicon cure. Never had any more trouble with black exhaust.

hi every body,, i have ASP40 and i have been running it for more than a 6 months now and i still get dark oil out from it,,one of my friend told me u r using the wrong kind of castor oil,he meant not pure kind of castor oil,is that true???

Are you using pre-mixed fuel from a reliable source, or are you mixing your own fuel? There are different grades of caster and various synthetic oils, and different oil mixes will change the exhaust residue color a bit.

However, black (not dark brown, black) comes from metal wear or from really burning the oil up, both of which are bad things.

Very dark brown is also often a sign that you are burning oil up, meaning that your engine is running too hot (usually, too lean) and burning oil. Or, if you mix your own fuels, or are using a no-name fuel, it could, in fact, mean poor quality oil as your friend suggested.

i check the fittings on the muffler and everything appeared to be tight. asked my trainer if we could have been running it to lean. so he richened it up a bit and we flew this morning. no problems engine ran like a dream and no black oil. guess it just needed to be riched up a bit. thanks again for the advice. now i can sleep better!