1. Preliminary Considerations

The oil in a 2-stroke engine performs two distinctly different functions. First and foremost, it lubricates the moving parts of the engine while it is running. Without a thin film of oil for lubrication between the pistons and the cylinder walls, the engine would self destruct in short order. Equally important to the life of the engine is the lubrication of rod bearings, crankshaft bearings, and piston pins.

The other function is that of protecting the internal parts of the engine as it sits quietly between flights, sometimes for weeks or even months at a time. The oil should cling to the internal parts, forming a thin film that protects against moisture and prevents rust.

Unfortunately, an oil that has excellent lubricating properties may not exhibit the best ability to form the protective film. Or, an oil that has good film characteristics may not provide the best lubrication. It's a tradeoff.

For 2-stroke engines, there is the practical matter of getting the oil into the engine. The oil is mixed with the fuel in a definite proportion and is then carried to the inside of the engine by the fuel as it passes through the crankcase on the way to the cylinders. The oil may be mixed with the fuel prior to putting the fuel into the tank (premix), or a special injector pump mounted on the engine may inject the oil into the fuel-air stream after it passes through the carburetor. When an injector is used, the oil is stored in a small tank or bottle mounted on or near the engine.

Injector pumps are favored by those who dislike the task of mixing the oil and the fuel, but others are skeptical of them because of their complexity and the nagging uncertainty as to whether the pump is really doing its job. At any rate, there are two methods (premix and injector) used to introduce the oil, and the method of introduction may impact the decision about which oil is preferred.

Yet another consideration arises because almost all the oil introduced into a 2-stroke engine is burned in the cylinders, quite unlike a 4-stroke engine. Therefore, a suitable oil for 2-strokes must burn clean without producing excessive deposits of carbon on the pistons and especially on the piston rings. A secondary consideration is the amount of oil residue that blows out the exhaust to be deposited on the tail feathers, the prop, and the rearward surfaces of the plane.

So, "Which oil should I use?" is not such a simple question after all! There are many things to consider, many competing factors, and in the end, a compromise must be made.

2. Three Different "Types" of Oil

There are basically three different types of oil available. We have straight mineral based oils, straight synthetic oils, and then we have something called a para-synthetic. The para-synthetic oil is a blend of both mineral and synthetic oils.

Mineral based oils are generally known for good lubrication properties while the engine is running and then, while the engine is sitting between flights, the mineral oils do a great job of keeping the internal parts of the engine coated with a fine film that keeps rust from forming. However, there have been complaints about excessive carbon deposits and stuck rings in some cases when straight mineral-based oils are used.

Synthetic oils are generally known for having excellent lubrication properties with low deposits while the engine is running. But, the super slick nature of straight synthetics has been accused of not being very good at leaving the fine film on the internal parts while the engine is inactive. The para-synthetics are touted as being the best of both worlds by providing the pro's and limiting the con's of both the mineral and synthetic oils.

3. The Most Popular Oils used in Ultralight Engines

There seem to be two main oils that ultralighters use. They are Pennzoil for Air Cooled Engines and Amsoil synthetic oil for 2-stroke engines. The Pennzoil is mixed at 50:1 while the Amsoil is mixed at 100:1.

Some reports state that Pennzoil gives the best lubrication while Amsoil or synthetics give the least carbon buildup and tail feather deposits. Mechanics have stated opinions from "no problems at all with Amsoil" to "Pennzoil gives better wear protection than Amsoil".

One contributor to this article writes, "I am inclined to listen to Tom Olenik when he says that he sees a little more engine wear with Amsoil at 100:1. I also note that Amsoil does recommend increasing the mix ratio to 80:1 for severe service conditions, which may include improper warm-ups or perhaps running at full throttle most of the time."

There have even been a few bad reports on Pennzoil and Amsoil but most, by far, are very positive. Early synthetics were reported to have an affinity for moisture. This problem is supposed to have been overcome many years ago. An obvious advantage to using synthetic is less carbon buildup and much less residue on the tail feathers, due to the simple fact that, at 100 : 1, there is less oil in the fuel to burn.

Some folks swear by Pennzoil, and other swear by Amsoil. Some swear at both so "your mileage may vary".

4. The Tried and True: A Recommendation

Now, for the person who just wants to know what oil to use in his engine without getting into all the esoteric details, here it is:

Pennzoil for Aircooled Engines mixed 50 : 1

Please understand, this is not saying that Amsoil, or any other oil is bad, and we're not saying that Pennzoil is the best, we're just saying that, overall, you will be "safe" with Pennzoil.

This recommendation is based upon years of experience with Pennzoil and the favorable reports of its use in hundreds or even thousands of engines.

To give you an idea of the strength of the convictions represented here, one contributor to this article does not use Pennzoil in his plane. He prefers a synthetic. However, all agree that, indeed, you will be "safe" with Pennzoil because of its track record, and also because the 50:1 mix ratio is a little less critical than 100:1 for the synthetic Amsoil.

5. Other Available Oils

There are Pennzoil 2-stroke oils formulated for marine or outboard use. While they may work, they are not recommended as the formulation is not set up for the air cooled engines. Some folks have used regular 2-stroke engine oils such as those from Walmart and other stores. Good results have been reported by some as well as bad results by others.

Other oils in popular use are Yamalube, AV2, Valvoline, Quaker State, Shell, Advance, and Golden Spectro, which is a blend of organic and synthetic oil.

One person writes, "I have been using the Golden Spectro for close to 20 years myself. My satisfaction is based on the performance and condition of the engines upon routine breakdown inspections."

6. Other Variables

There are lots of brands and lots of claims. However, keep in mind that there are many other variables that come into play that can allow someone to have success or failure with any of the oils. Here's some food for thought.

Say we have a guy in the North-Eastern, colder, wetter climates that uses a straight synthetic oil. He discovers rust on the inside of his engine upon tearing it down. A guy in the dry South-West, using the very same oil, might report that his engine is clean as a whistle and rust free. We might prematurely conclude that the straight synthetic might not be the way to go in the wetter climates.

What might the guy in the North-East do to change the outcome of his tear-down inspections? For one, he might follow the most recent guidelines from Rotax for storing the engine when not in use. Some of the recommended items include carb covers and plugs for the muffler to keep moisture from entering the engine when not in use. Long term storage should include draining the fuel system, fogging the engine with oil, and so forth.

Several years back, Ultralight Flying magazine did a survey on engine oils. This was an attempt to determine what oils were being used and what complaints the users had that might be associated with various oils.

Surprisingly, three oils were touted as having the least number of complaints that could be attributed to oils. Belray had two products included in the three, and the third oil was Golden Spectro's para-synthetic.

It should be pointed out that the results of this survey probably fall far short of being scientific. It would be interesting to see truly unbiased results of a survey of all the oils that are in use in various scenarios and climates.

Perhaps it's a bit too easy for manufacturers to construct tests to make their own oils outshine those of the competition under specific circumstances. In turn, this makes it nearly impossible for a consumer to do a meaningful evaluation of one oil relative to another.

More important than the oil issue is the carb tuning and proper fuel mixture. Most of the oils available today can do a fine job of lubricating the internal parts of the engine. If a guy were to select a premium low ash oil known for having a cleaner burn, he can negate the benefits of the oil by running the engine too rich which can cause more deposits than normal.

By the same token, someone could have better than average results with a low end oil if his carburetor was carefully and expertly tuned. Two many variables come into play for it to be possible to guarantee certain results with Brand "X." Jetting, fuel octane, temperature, altitude, and many other factors can enhance or negate the success achieved with a particular oil.

7. Conclusion

Hopefully, this article has added to your understanding of the complexities associated with the apparently simple matter of choosing an oil for your engine. Admittedly, we have not provided a lot of firm answers. But, we did make a recommendation to get you started.

As you gain experience with your engine and acquire knowledge of its peculiar traits and mannerisms, all the while talking to the local experts, you may come to prefer one oil over another. That is just fine. After all, the variables to which your engine is subjected may be quite different from a similar one not all that far away.