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Products - Frequently Asked Questions (FAQ)

The oil that accumulates on my model is very dark in color. Does this mean that my engine has a problem?

Not necessarily.

When a model engine operates, the oil in the fuel is not consumed, but carried away with the burnt gasses. This oil will then accumulate on the model. Depending upon the position of the exhaust outlet on the muffler or pipe, and the airflow around the outlet, there may be a light or heavy accumulation. Model airplanes tend to have heavier accumulations of this spent oil than other types of models.

Because the oil has been heated by the combustion process in the engine, and also comes into contact with the exhaust system, it will begin to degrade. Different oils will react differently. Many synthetics will actually start to "cook" from the heat. It will exit the exhaust system and put a dark film on the model.

Dark oil does not necessarily mean that your engine has anything wrong or is suffering abnormal wear. To determine that, you have to examine the oil.

If the oil is clear, but just dark, then it's only the oil that's burning. It could be "cooking" in the combustion process or because of being exposed to the hot exhaust system. Different types of oil will be lighter or darker. Even one type of oil will react differently in different engines because of the temperatures of their exhaust systems.

If the engine actually has something wrong, then the oil residue will be very black, almost opaque. If you examine the accumulation carefully, you may see small sparkly metal flakes floating in the oil. This means your engine has something seriously wrong.

The best way to examine the oil is to capture part of the exhaust stream on a piece of white card stock. A white notecard is ideal. Hold the card so that a puddle of exhaust oil accumulates, then set the card aside for a few minutes. The oil should be absorbed by the card. Once the oil's been absorbed by the card, you can see if there is any solid material left on the card's surface. Sometimes, it's carbon. Sometimes, it's metal.

Carbon comes from the combustion process and is usually a result of very-rich running. Castor oil will tend to carbonize.

If the solid material is metal, you then have to determine its source. Sometimes, the metal gets into the exhaust stream from the exhaust system. It may be vibrating against the engine's crankcase, or a tuned pipe may be vibrating against the header. This is annoying, but not damaging to the engine. You may have to tighten something, or add an insulator to prevent it. To verify this, run the engine with the exhaust system removed, and collect more of the engine's exhaust stream on a card. Be sure to wear hearing protection!

If you still have metal in the exhaust stream, then something in the engine is seriously wrong, and your engine needs to be torn down and carefully examined to determine the source of the metal. There could be a number of difficulties causing the engine to "make metal". You may wish to send your engine to the service center to determine the problem and correct it.

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