Dear all,
When I started nitro, I usually buy fuel from my LHS with a 5% nitro. After flying for some time, some of my friends recommended home mix fuel which I believe the composition is 1 part castor oil and 4 parts methanol. I found that after using the home mix fuel, my plane is all covered with black slug oil coming from the exhaust after one flight. This is not the case when using the 5% nitro. While there's still some oil covering the plane when using 5% nitro, it's not as much and black as using the home mix fuel. My friend say that the large amount of black slug is good for the engine as it more less help to lubricate the piston to make the engine last longer. In cases where nitro are use, it'll wear out the engine faster. The more nitro content, the faster the engine wears out. Please let me know whether this is true and if any experts out there can give me some theory on this issue, it'll be greatly appreciated.
Thanks in advance.

The black sludge is probably residue from castor oil, which the homeade fuel must use. Exhaust residue should be brown, if colored at all. Pure black usually means aluminum residue in it, a bad sign of a too-lean mix or something rubbing in the engine. You can roll the residue between your fingers and feel the particles, or even see them glinting in bright light. Personally, I'd stick with commercially manufactured fuels. They are usually more consistently mixed and have less contaminants. It's hard to improve on the fuels that are commercially available. If your engine is an ABC/ABN type, use fuel with a castor/synthetic oil mix, like Morgan's Omega. If your engine has a lapped iron piston or rings, you should use pure synthetic.

Dr.1

You just stepped into a deep pond where ther are as many opinions as there are modellers.

Here goes:

1) don't mess with home brews -- they usually cost as much, or more, than commercial fuels & if you don't use top-grade ingredients & know what you are doing, they can wreck your engine.

2) Black sludge can either be burnt castor or metal particles. Burnt castor can indicate that your are not using a suitable grade of castor, or it can indicate that you are running to hot (lean). Metallic particles may be from rapidly wearing internal components that are inadequately lubricated, or they may be from vibrating exhaust components.

3) Nitro, if used in sane quantities, won't shorten your engine life as long as you ensure that nitrated fuel doesn't sit in the crankcase for extended periods after engine use.

Agree, use commercially available fuel. I have engines that I have been running 25+ years. I do however dissagree with the statement that you shouldn't leave fuel in the engine after running. I have never run an engine dry after a day of flying. The nitro in the fuel evaporates almost immediately, and all that is left is oil. It protects the engine. My friends that burn it out after are always replacing bearings. I got one of them to stop running out the fuel afterwards, and he hasn't lost a bearing since.

I like 15% nitro, 20% oil fuel myself, and usually use a castor synthetic mix. Have used just about every brand of fuel and many different mixes. The last order I placed was 100 gallons of Red Max. Byron was good, cool power was good, and many others. As long as the oil is 16 to 20% and its not old, it will do fine.

I tend to stay away from peoples home brew fuel. I never saw the point to it. The guys here using it were the ones flying junk planes and wrecking just about every flight. Their engines never last long enough to worry about.

FHS has great deal on Red Max if you buy in quantity. Look them up on google, get a bunch of friends together and get a big order. It beats paying the high prices you see at a lot of hobby shops. Our hobby shop is over $20 a gallon. I won't pay it. I get it at the shop in Kalispell if I am there and need it. They are usually pretty fair on price.

As I said -- lots of opinions. I should have been more specific -- I was alluding to not leaving high-nitro content fuel (25% for example) in the crankcase. I use 10% - 15% & I leave the fuel in there during the flying saeson, but I use after-run oil during long periods of non-use.

Yea Brit, everyone has their own opinions. Thats the fun of the hobby. I use oil too for storing and such. Many like the marvel tool oil and other oils like that. I have used marvel regular mystery oil, but if you leave it in too long, it gets gummy. Soaked in marvel it loosens right up again though. Too much oil is better than not enough.

Thank you all guys,
This is ton of information and really appreciate the fast response. However as I said earlier, I had used about a gallon and if I were to switch back to 5% nitro, will it effect the engine. And will this one gallon of home brewed fuel do much harm to my TT .46 pro?
Thanks.

bemyself,

Model airplane fuel is composed of three ingredients; methanol, nitomethane, and lubricant. The lubricant component is usually a mix of synthetic and castor. In my case I use a blend of 12 1/2 % nitro and 20% lubricant ( 18% synthetic and 2% castor). The castor will help in preventing excessive heat, but tends to leave varnish deposits on the engine, hence the small castor percentage.

The nitro - lubricant percentages are not directly related. In other words, the nitro content is separate from the lubricant. The nitro content can be 5%, 10%, 15% or even 20%, or anything in between, but the lubricant would be constant at 20%. If I understood your post, it seems to me your "home brew" had way too much castor.

That's my understanding of fuel. Hopefully someone with more knowledge on the subject will add a post.

DaveB

Switching back won't hurt your engine, and I would highly doubt that running a gallon of home brew hurt your enigine. Most guys put a ton of oil in theirs anyway. I doubt you have a problem.

Away for a few days and no time to read the thread.
Thanks alot for all the info.
Regards,
Bemyself

I do the same as you, Flyboy. I shut the engine off hot at the end of the day. I figure, with the hot engine, the nitro and alcohol evaporates leaving just the oil. Havn't replaced a bearing yet.

Hello!
Having black oil comming from the engine is not good and indicates that you have set the engine to lean!!
Ofcourse you can go back to the 5% nitro blend.
At my club here in Sweden most people (130) blend their own fuel, and so do most people in all the big clubs around here in Stockholm (Capital of Sweden).
Glow fuel is just Castor oil (or synthetic or a mix of the two), metanol and nitro (nitro is not necessary).
Over here in our club, and the rest of Sweden it is very common among fliers to use 10%-15%all synthetic oil and 5%-10%nitro.
Regards!
Jan K
Sweden

bemyself,
I think, too that you're overdoing the oil in your home brew. Back many, many years ago (mid 1960s) when I was a fledgling modeler living in Hong Kong, castor oil and methanol were readily available and reasonable in price, whereas commercial glow fuel was horrendously expensive and hard to come by. Is this the case in Thailand?
As I remember, my formula was 4 parts methanol to 1 part castor oil like yours. Yes, you will get a gooey sludge running pure castor oil and part of the problem could be the quality of the castor oil. (I remember that the castor we used to buy back then differed in color and viscosity from batch to batch). It couldn't hurt, though , to richen up the mix a bit, especially if you see metal bits.
Just thought I'd share a bit of my own experience. Good luck.

papermache

one thing I left out. If you're getting a LOT of sludge, try using a bit less castor. Maybe a 4.5 or 5 to 1 mix. Also if you can find a source for some synthetic lube it might make things a lot better. Whatever you do, do all your testing on the same engine. If you burn up one engine it's a lot less expense than if you do the same to several.

papermache

Thanks for all the information. I think I'll revert back to using the Omega fuel with 5% nitro which cost about 15 usd per gallon.
Thanks once again