Hi there, I was wondering if it is really neccessary to add oil after my flying day is over, I am flying super tiger .45 & .61, what are the pros and cons to doing this? Also some body at the club told me they use air compreessor oil, and hydraulic fluid also, he said its just as good but much cheaper. Is it true? any help would be trully appreciated. thanks.....peppster...

I learned this from a guy with over 30 years in the hobby. He taught me this. After run oil is designed to keep the engine well lubricated and to avoid rust from setting up in the engine after you run it and then let it set up for even a short while. Likewise, he recommended to run the fuel out of the engine after the last run of the day and after removing any remaining fuel in the tank. Glow fuel can really gum up after it sets for a while exposed to air. The nitro evaporates leaving a gummy mess. Not good for the engine. Leave the carb set to the wide open setting so the engine can get air and not be closed up. Don't plug the muffler or the carb with a paper towel thinking this will keep it clean. It actually causes it to keep any moisture inside the engine which only adds to the potential of rust from the moisture.

As for the oil to use, well, I use 'after run oil'. The amount used is only a little so the cost is really not an object when you consider the value of the engine. Squirt a little in the carb. and then use your starter to turn the engine over several revolutions. Are there other oils you can use? I honestly don't know. Just my 2 cents and what a good friend and experienced pilot taught me. So far so good with no engine problems. I guess it's working..........

After run oil is just transmission fluid...cheap at the autoparts store. Don't spend $3 for a little bottle of after run oil.
JustMe

The following is not based on any scientific evidence, only the experience of a lazy pilot.

In the past 11 years of flying I have never used after run oil and I cannot tell that it has caused any problems. The first couple of years at the end of a days flying I would pump the remaining fuel out of my tank and run the fuel out of the engine. Now I only pump the fuel from the tank, leaving fuel in the engine. None of my engines show any signs of rusting.

None of the small group of guys that I fly with use after run oil and like me they have not experienced problems. The best/safest thing to do may be to use after run oil, but as long as I have good results without it, I will continue my lazy routine.

Eric

RFW1953: That gummy mess that is left after the methanol and nitromethane evaporates is the oil in the fuel which IS good for the engine.

What isn't good for the engine is the nitromethane and the methanol. Nitro can break down into an acid which will etch the engine parts and the methanol attracts water. Adding an after run oil to the engine is supposed to help keep the nitro & methanol/water off the parts. This really only works properly if you vent the engine and work the oil in good. Many oils will work fine.

I never bother with after run oil. I always tear my engines down in the winter and rebuild them. I soak everything in oil (Mobil 1 Synthetic 10W-30 motor oil) when reassembling. Some of my engines will get fed 30 gallons of glow in one season, no after run oil, they look fine inside.

Cheers

For castor fuels after run oil seems to be a WOFTAM for synthetic fuels i have no idea

I have never used "after run" and have never had a problem. Maybe using it in the winter, when you don't fly as often might be a good idea.

Nitro can break down into an acid which will etch the engine parts and the methanol attracts water.

Nitro only breaks down to an acid when burned, however it forms nitric acid which is a very unstable rocket fuel, this then burns with the methanol. So it is not much of a problem. However pure nitromethane is a very mild acid itself, but not as strong as vinegar or lemon juice. About a PH of around 6.7 I think. IMO a non-issue, unless you are a speed racer running 70% nitro. Even then only the cylinder and exhaust stack are exposed to any significant amount of nitric acid.

In over 27 years of flying I have never used it. There is enough oil in the fuel to take care of the engines. I have friends that have not been flying as long and they run the fuel out after every day of flying and use after run oil. They are constantly replacing bearings. I have never replaced one. I have some really old engines too. From my exp, after run oil and running the fuel out does more harm than good. Everyone has thier own opinion, thats mine. Noone is right or wrong, its just the way different people do it.

I still have the original bottle of after-run oil that I bought in 1977. Shows how much I use it. (I only ever use if if I change engines on an airplane and bag the prior engine up for storage) Never had any problems caused by leaving some fuel in the engine either.

As for fuel left in the tank - well, it's just about impossible to remove ALL of the fuel (the clunks are not that efficient), so if you leave the tank almost empty, it doesn't take all that long for the remaining methanol etc to evaporate and leave the gooey residue behind, whereas if you intentionally leave a bit more fuel in the tank, it takes that much longer for the methanol etc to evaporate, so it's easier to slosh the tank out if you end up leaving the model unflown for several months.

I also won't leave the carb open. That just asks for dirt to find its way into the engine IMO.

Gordon

peppster , are you lol as much as I am? This was a good question that you began, and today I too learned something. I think I'm going to throw my bottle of after run oil away. Thanks for the education on this topic guys. By the way, do you use STP in your automobile? If not, I have some i'll give you. I bought that too

I have never used after-run oil in my engines either. No problems. I use Cool Power fuel, and their ads say that no after-run oil is needed. I always drain the fuel out of the tank, but do not run it out of the engine. After three years, so far, so good.

Ok, I'll throw out the counter point.

For years, I never bothered to run the engine dry or use after run or anything, and never had a problem.

However, recently, I got in to flying combat. In combat, it's not uncommon to fly a plane just once in a trim flight before a contest and never again that day. Like 2min flight, max. All of a sudden I rusted a couple of sets of bearings. Not in my primary planes, that get run alot, but in the backups that run once in a while.

Now I use Automatic Trasmission Fluid as after-run and I've had no problems since. I use a good squirt of it too, none of this wussy "3-4 drops", that's not nearly enough to coat anything.

Ok, so why did I suddenly have a problem, and why do these guys who burn fuel by the drum never have problems? I think it comes down to engine heat. An engine that is run at full temp, and shut down with out a prolonged idle will (I think) boil off any remaining fuel in the engine before it cools off, leaving nothing but oil, and so it doesn't rust. Run an engine just once, for a short bit, or run it at idle for a long time, and the engine does wind up with liquid fuel in it over time. And that attracts water from the air, and leads to rust.

A couple of other factors I've though of that might, or might not, play a part. Some engines use cheaper bearings and metals in some of the parts than others. I haven't done a "study" but it does seem to be more of the less expensive engines that rust up.

I haven't heard about not plugging up the exhaust and carb. I have started to do that to keep stuff from dripping in the car these days, something I didn't bother with in the distant past (before I was married).

But I do think the biggest difference is how you run the engnie, and how often.

That's my story, and I'm sticking to it.

Kirk.. I must say I like your approach... it's a plausible explanation.. ahot engine should evaporate the residual nitro & methanol fairly quickly...
Just to let you know... down here (in Honduras) as far as I know nobody uses after run oil... we do clean the engines..
a friend of mine "resurrected" a 20 yr old K & B which was "stored" in a back room subjected to dust.. dirt.. high humidity (we're about 1000 yards from the beach) was not in a sealed bag or anything... it started fine and so far keeps on ticking...
On the other hand.. specially 4 strokers (YS, saito , etc) appear to be in need of after run oils...for what i've seen in other threads, also the quality of bearings must play a role.....

I'm another one of those who has never used it. (been flying for over 40 years)