Why Choose Oil Injection on Rotax Aircraft Engines

by Michael A. Anderson

Why Choose Oil Injection on Rotax Aircraft Engines?

Why Choose Oil Injection on Rotax Aircraft Engines?All Rotax 2-stroke Aircraft Engines (except the 447 UL) are now provided with an oil injection pump. But because of a lack of an adapted mounting system (as is the case for the Quad City Challenger / Challenger II ultralights), or because of dubious superstitions, some planes are still not equipped with oil injection.

The principle of oil injection rests in the separate intake of oil and fuel/air mix rather than the premixing of both. An engine driven pump regulates the flow of oil and injects it into the engine via the intake manifolds. Such systems have been used on 2-stroke engines since the early 60s, but it is only since 1989 that Rotax has been using them on their aircraft engines, starting with the first 582 UL. Faithful to their tradition of reliability, Rotax waited for the system to be thoroughly proven before using it on their 2-stroke aircraft engine range.


  • More convenient
    No need to premix your fuel. Simply fill up with pure fuel and ensure that your oil tank is always topped up.
  • Less carbon accumulation
    The major part of carbon accumulation in 2-stroke Aircraft Engines takes place at idle, a speed at which they do not actually require as much as a 50:1 ratio of oil. The oil injection pump regulates only 70:1 at idle, therefore limiting carbon accumulation. At higher RPMs, the ratio is brought back up to 50:1.
  • Less engine wear
    The lower amount of oil at idle also helps prevent the wear caused by excess carbon deposits.
    With oil injection, the oil circulates through the engine better and ensures better lubrication. Furthermore, the alcohol contained in the majority of fuels reduces the oil’s lubricating efficiency when pre-mixed. Oil injection prevents this reaction from happening and ensures that the oil maintains its peak efficiency.
  • Cleaner inside
    When oil injection is used, only pure fuel flows through the fuel system and carburetors, keeping everything clean. Otherwise, when premixed fuel evaporates, it leaves the oil’s varnish deposits behind, quickly contaminating the fuel system and carburetors.
  • Cleaner outside
    An oil injected engine’s emissions are reduced thanks to the lower oil ratio at idle. In addition to the environmental advantages, the difference becomes quickly obvious in terms of exhaust deposits on your aircraft and propeller.
  • Eliminates the risk of pre-mixing mistakes
    How many times did you ask yourself if you did put the right amount of oil in your fuel? Or if you even forgot to add it? Those risks are completely eliminated. Simply keep the 2 litre (about 5 hour’s flying capacity) tank topped up. A level sender can even trigger a warning light on your instrument panel to indicate low oil.
  • Preserves octane rating
    Most 2-stroke engine oils cause the fuel to lose up to two octane points when pre-mixed.

Installation criteria

  • The tank should be placed so that its outlet is always higher than the pump under any flying attitude, so that the pump is always gravity-fed
  • The oil line and oil filter have to match Rotax standards
  • A few precautions have to be taken during the first run: It is important to bleed the system to free any air bubbles; the oil injection lever cable has to be adjusted so that the marks on the lever and pump align at idle; the first tank should contain 100:1 premix to ensure that the engine will receive adequate lubrication while any last air bubbles go through

Don’t wait!

  • On a new engine:
    Your new engine will be provided with an oil injection pump. You will just have to add an oil injection tank and a 3-way throttle control cable to actuate the pump lever in addition to the two carburetors.
    Note: Certain manufacturers (notably Quad City, manufacturer of the Challenger) provide an engine without oil injection with their kit. It is more advantageous for you to buy your engine through us since for the same price you will have oil injection included.
  • On an existing engine:
    Most existing engines of types 503 UL, 582 UL and 618 UL can have oil injection retrofitted. You need to add an oil injection pump and change the intake manifolds. You will also need the oil injection tank and a 3-way throttle control cable to actuate the pump lever in addition to the two carburetors.