Rotax four stroke aircraft engines have proven themselves as reliable pieces of machinery. They can be bought as experimental (UL) or certified (A and F) engine and there are four main models (injected too) to date. The original engine is the 80 hp 912, from which the 100 hp 912S was developed and Rotax also has a 115 hp turbocharged 914 engine. In 2015 Rotax announced the 135 hp fuel injected turbocharged 915iS.
Field experience has led to an updated list of oils approved for the Rotax 912 and 914 engines. Particular usage profiles and the use of a turbo charger on the 914 engine, rich mixture due to carb heat, prolonged idling and the use of AVgas leads to deposits in the oil.
This service instruction recommends a list of oils to be used in these engines.
SI-18-1997-r5, Oil Specification
Excerpt from the document:
Due to field experience the recommended engine oil list (section 3.2 and section 3.3) was updated. Field experience has shown that additional information about the choice of suitable motor oils and oil change and maintenance intervals for the ROTAX engines Type 912 and 914 is necessary. Regardless of which brand of fuel is used, foreign particles are suspended in the motor oil. Heavy accumulation of particles on high temperature zones such as on piston rings, exhaust valve guides, may result in stuck piston rings and valves due to burning and coking of the oil.
On the turbocharged engine, failing to ensure an adequate cool-down period prior to shut-off may lead to particle deposits on the turbocharger wheels. This could result in an unbalance of the turbo wheel and consequently to a complete destruction of the turbocharger. Particle deposits or cooking may become loose in the engine and may block the lubrication system causing damage to the engine due to lack of oil.
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