I'll kick things off here.

How may of you guys are using 2 stroke fuel in your 4 strokers and what are the advantages or disadvantages?

Until recently I had been using Fox's 50%/50% in both two and four strokes. I got a RCV .90 and got the Recommended WildCat Premium Plus for it, so I'll use the Fox in two strokes and the Wildcat in four strokes and see how it goes.

I have been using omega 15% two stroke in both my 4 stroke engines with no problem. However, I have had two guys tell me that my 4 stokes will run a bit cleaner, and a little better on 4 stroke fuel. Has to do with the right oil content.

I was running the 15% four stroke fuel (Omega) in my 4 stroker and the muffler quickly became a brown nasty mess. I was told from the guys at the field that this is from the castor content and going to a 2 stroke fuel would run cleaner, avoid the muffler problem and work fine as well. This advice came from an engine machinist who really knows his stuff about model engines. Either one appears to be ok but the only downside of the 4 stroke fuel seems to be the brown glaze from the burned up castor on the muffler. A wire brush will clean it up though.

The only difference between four/two stroke fuels is the fuel manufactures actual oil content.

For instance most four-stroke engine manufacturer's suggest running a higher percentage of oil by volume than their two-stroke cousins.

Four-strokes generally call for 18-20% oil.

Two-strokes range from 15-18% oil.

The other considerations are Nitro content and oil type...

Most engines [not all] respond to higher percentages of Nitro very well. 30% Nitro is very common and has proven to be safe. More expensive but does provide some benefits. i.e; improved performance, improved idle, cooler running engine. Four-stroke engines really come alive with 30% Nitro.

Oil is another consideration. Most user's regard synthetic as the answer to all. I use 100% synthetic oil by volume in my sport engines. My engines that are leaned on [not leaned out] and abused for racing such as my YS Engines 120-SC's and two-strokes, I am using a fuel such as Wildcat's Pro-Blend. It is offered in various Nitro percentages with typically 18% oil by voume with 95% of the oil mix being synthetic and the 5% balance being good old fashioned Castor Oil.... The Castor Oil offers some benefits not found in synthetic's. Castor Oil is superior in heat transfer, does not break down as early as synthetic when exposed to high temperatures and works as a rust inhibitor.

In the small ratio as I have suggested I have never had any negative problems with the use of Castor Oil...

Hey guys,

I was speaking to the owner of our LHS just last week about the difference in the 2. I use Omega's cool power 15% in my 2 and 4s engines. The owner was telling me Olmega's cool power and their 4 stroke fuel both have the exact same content. He said when he approached them and asked the difference they would not respond other than the label. Seems like a way to make more money on their part. I've seen the contents myself. Same nitro/oil?? Hmmm..

I have heard a lot about the different oils. It is my understanding that castor oil works better the hotter it gets, and that synthetic does not stand up to the heat of combustion very well. I think it would be best to use a good % of castor in your fuel. The synthetic will be great for the bearings, but the castor is even better for the piston area.

My .02.

I checked on Cool Power for my 4-strokes. Their 4-stroke pattern fuel contains 20% oil (this is on their website). Cool Power 2-stroke fuel contains 17% oil (this is old information but I believe it's still correct). Several of the AMA pattern guys here are running the 4-stroke Cool Power pattern fuel in their YS's with excellent results (YS 1.40's require 20% oil).

I've been using Powermaster 2-stroke 15% nitro fuel in my OS 4-strokes. The OS instructions say use a fuel with 18% oil and this is what the 2-stroke Powermaster has. Just don't run the engine too lean. If you want some insurance, add a little extra oil.

I have been thinking about switching from Omega, to Cool power, for both my 2, and 4 strokes. What is the difference in the two?

Not sure about all the engine manufacturers but Saito will void their warranty if you use 4 stroke fuel in their engines. They state to only use 2 stroke fuel.

Four stroke fuel has less oil in it. Some four stroke engine manufacturers tell you NOT to use four stroke fuel in their engines because of this. Most four stroke engines are ringed and typically like synthetic/castor blends...heavy on the synthetic. Most two stroke engines are ABC and like the same blend but heavy on the castor, there are some exceptions. Typically four stroke fuel will have 15-18% oil and two stroke fuel will have 18-22% oil, there are some exceptions. I personally use the same fuel, 10% nitro/20% oil (mostly castor), in all of my glow engines...period! My planes are a little greasy at the end of the day...SO!...my engines are in excellent shape!

It is ALWAYS good to err on the side of a little more oil if you want the longest possible life out of your engines. Speaking of oil...don't forget an after-run oil after each day of flying either! If you use a heavy castor oiled fuel in a ringed engine this is imperative! I use Marvel Air Tool Oil...you can get a quart at a auto supply house for ~$6...cheap!

I've been told that Coolpower has only 17% oil. So I won't use it in my OS 4-strokes without adding some extra oil. As I recall it uses only synthetic oil. Otherwise it's a good fuel.

U used to run Byrons 20/20 thru all of my engines but I've switced to Magnum #1 for all my saitos as well as my 2 opperational Helis. I always add about 2 oz's of Klotz per gallon of fuel (3 -4 ozs if it's a real hot summer) All of my enignes love it..smooth low idles and loads of power.

After doing even more research on this and some discussions with some knowledgeable people on this topic I'm going to use my 2 stroke fuel also in my four strokers. 15% nitro and 20% oil. You may lose 100-300 rpm because of the replacement of oil instead of the alcohol component but the other side of the coin is the engine will last much longer and if your a sport flyer that is an easy trade off since that small an rpm drop is negligible (most of use overpower anyway).

I think unless you are a maximum performance competitor and don't care about burning up engines much sooner than necessary just in order to tweak a couple hundred extra rpm than going with the 2 stroke fuel w/20% oil is the answer. Even Saito as stated above will void the warranty if you use 4 stroke fuel! That should tell you something...

I guess it's a matter of application...all out performance vs. engine wear and longevity. For the 90% that are sport flyers I would think that longevity would be preferred.

Now I just have to burn the rest of my 4 stroke gallon off! Maybe I'll add an ounce of Klotz since the motor is still semi-new.

Also, Gene mentioned to use an after run oil but also should add to that to avoid certain after run forumulations in certain engines as it could damage o-rings/seals.

I recently purchased a 4 stroke engine and I too do not want to buy 2 separate types of fuel. I did some research on this and found out that it is pretty critical to the life of a 4 stroke engine to have caster in the fuel. I believe someone else mentioned that synthetic doesn't stand up in the extra heat of a 4 stroke. So, what I finally came up with is this....get the 2 stroke fuel of your choice and add a small amount of caster oil to it. I have been doing this in a smaller bottle. I add 1/4 oz caster to 10 oz fuel. This should bump the oil content up by 2%. So you can buy the fuels with less oil in them such as 18% and bump it to 20%.
good luck to all Jeff

I have been useing Byron 10% 2 stroke fuel(caster blend) in all my four-strokes for the past 7 years
and never had a problem yet. Idles are very reliable.
Derek

"synthetic doesn't stand up in the extra heat of a 4 stroke"

4 strokes do not run hotter than two strokes. At say 10k rpm a two stroke has 10k explosions /min. A four stroke has 5k/min. no heat is caused by an exhaust stroke. They do not run half as hot but they do run cooler.


Ed S

Sorry, even though 4 strokes fire 1/2 as often as 2 strokes they actually run as hot if not hotter than 2 strokes. This is based on personal experience over the years and a hypothetis:

In a two stroke, raw cold fuel is drawn into the engine through the low end. The intake of fuel cools the engine's low end as it is processed into the engine, burned and exhausted. There is no low end cooling by raw fuel mixture in a 4 stroke because the fuel is directly sent into the combustion chamber from the top of the engine intake valave.

The only lubrication of the low end on a 4 stroke occurs blowby gasses containing unspent oil. Not enough blowboy occurs to actually have a significant cooling effect on engine, just enough to keep the moving parts slick and prevent them from seizing up.

A 2 cycle engine running 300 rpm shy of max lean can be touched for about 2 seconds before a burn occurs. A 4 stroke running 300 rpm shy of max lean will cause an instant burn if you touch it. Not very technical but observation and analysis are the most basic of scientific principles.

Coolpower 15% is 17% oil, 100% synthetic
Coolpower 15% 4 stroke fuel is 17% oil but contains some castor in same proportion as Omega (its the same stuff as Omega but different color0
Coolpower 20/20 contains 20% synthetic oil.

Omega/Coolpower 4 stroke fuel contain too much castor in my opinion for 4 stroke use. If you are a good needle tuner and run your engines lean and understand that an engine leans out in flight when you burn fuel due to differences in fuel tank head pressure than you can get away with using synthetic fuel in all of your engines.

I've been known to burn 2 stroke coolpower in all of my engines. For the 15% stuff that contains only 17% oil, I add 4 oz of castor to each gallon. When I burn their 20/20 in my 2 and 4 strokes, I add nothign to the fuel.

I would suggest you read the book entitled "Model Four Stroke Engines" It is written by Peter Chinn, an acknowledged expert on model engines.

Ed S

I agree that the theory that a 4 stroke runs cooler is accurate because it doesn't fire as often as a 2 stroke but I don't think it applies to our model engines. My personal opinion is based on personal observation.

Also, another point which should support my opinion:

IF 4 STROKES RUN COOLER, WHY DO THEY MAKE SUCH POOR HELICOPTER ENGINES? Almost every 4 stroke heli engine (regardless of size) seems to overheat when used in the summer months. Most 4 stroke heli pilots say their engines perform best when it is cold out? Why do 4 stroke heli engines overheat when the 2 stroke ones don't? Don't say it is the size of the motor, if it was the manufactuers would have switched to larger 4 stroke motors for their helis by now. Heli's have cooling fans to cool engines but for some reason the 4 bangers don't run as well.

Any takers?

I do not know enough about helicopter applications to answer your question. Maybe it has nothing to do with keeping them cool. Whenever I have seen helicopters the engines seem to be revving like crazy. A two stroke will develop far more horsepower than an equivelant size four stroke, but at a much higher RPM.

Maybe the higher revving two strokes, going through the gear train are the only way to get usefull rpm at the rotor.

That is not a statement by me it is a question.

Ed S

Actually in theory, 4 strokes would be far superior than 2 strokes for helicopter operations. Helis need TORQUE to spin the rotor rpm. Head speeds for RC helis are between 1600-1900 rpm (a good general figure) and 2 strokes must rev high rpms to acheive the necessary torque through reduction gearing to turn the rotors.

4 strokes develop more torque than 2 strokes and need less of a gear reduction to turn the rotors at desired head speed.



So, can anybody know why a 4 stroke overheats in helis? I still think its because RC 4 strokes generate more heat than RC 2 strokes which receive additional cooling from methanol fuel mixture flowing through the engine's intake. (the term latent heat of vaporization comes to mind, but I'd be talking out my arse if I said that was the scientific principle behind it)

I have been using Cool Power 15% in my two and four strokes for years. (been flying for 15 yrs) I still have the OS .40FSR that I started with, and it was used when I got it. Still flying with it. The only work done on it was I had to replace the the front case because of a crash, it still has the orginal ring and bearings. Ialso have a OS .91 Surpass that is about 8 yrs. old. It has out lived a couple of planes. I was always told the 4-stroke fuel has less oil in it. Also be careful using the ST blend in the later model ST3000 and 4500, Ifound this out the hard way! I found out that ST recommends that if you use synthentic it needs to be at least 15% oil. I use 5% or 10% CoolPower for this.

I agree with Ed. it is a FACT that 4-strokes run cooler. That is the whole purpose of 4-stroke fuel. The problem with 2-stroke fuel as mentioned above is the extra oil cools the glowplug on the non firing stroke. That is why with a lower oil content you get a lower idle and smoother operation in a 4-stroke.

I would also suggest that book as good reading.