The how and why of Rotax Aircraft Engine instruments

Here is a brief description of the recommended instruments for Rotax 2 and 4 stroke Aircraft Engine monitoring and the reasons why they are necessary. These informations and much more can be found in our Engine Maintenance Logs.

At Aero Propulsion Technologies, we designed a cheat sheet in business card format which shows you the allowable temperatures for your 2-stroke engine. Ask us for one or print one yourself by downloading the following file: 2STref.pdf / 312Kb / Adobe Acrobat format

Rotax 2-stroke Aircraft Engines

• Cylinder Head Temperature (CHT) and Liquid Temperature
  The cylinder head temperature instrument is very useful on an air-cooled engine. It is less so on a liquid-cooled engine, where it is replaced by a liquid temperature instrument.
  On an air cooled engine, it is recommended to have a probe for each cylinder, as both cylinder heads are separate. A liquid cooled engine, with its joined cylinder head, only requires one probe.
  In both cases, it is important to regularly monitor the temperatures in flight as abnormal overheating can indicate a cooling problem, faulty lubrication or too lean a fuel/air mixture.
• Exhaust Gas Temperature (EGT)
  This instrument is very useful on any type of engine as it offers an insight on combustion temperatures. It is wise to monitor it in flight but it is particularly useful on the ground for carburetor tuning. Too high a temperature indicates too lean a fuel/air mixture, while too cold a temperature indicates a rich mixture. Adjusting mixture to the ideal temperatures allows the engine to run at optimal efficiency.
  It is recommended to use one probe for each cylinder to ensure they run in unison. Please note that the readings of certain CHT and EGT probes are affected by ambient temperature. Check your instrument and probe instructions for details.
• Tachometer
  The tachometer measures the number of revolutions the engine performs per minute. It is useful in evaluating engine performance. For example, too low or too high a maximum engine speed at takeoff can reveal a problem. It is also useful in setting the propeller pitch to allow the engine to reach its optimal takeoff and cruise speeds.
• Hourmeter
  This instrument counts the number of hours your engine has been running. It is particularly useful in keeping a maintenance log!
• Aero Propulsion Technologies offers a full range of engine instruments

At Aero Propulsion Technologies, we designed a cheat sheet in bookmark format which shows you the allowable temperatures for your 4-stroke engine. Ask us for one or print one yourself by downloading the following file: 4STref.pdf / 153Kb / Adobe Acrobat format

Rotax 4-stroke Aircraft Engines

• Oil Pressure
  The oil pressure instrument monitors the proper operation of your engine’s lubrication system. It may reveal a low oil level, leaks, restrictions and other system malfunctions.
• Oil Temperature
  The oil temperature instrument allows you to ensure that your engine’s lubricant is operating at the proper temperature. Oil lubricates optimally only within a specific range of temperatures which should be reached at warmup and preserved at all times. It may reveal insufficient or excessive oil radiator cooling and may reveal some lubrication system malfunctions.
• Cylinder Head Temperature (CHT)
  We found that many pilots confuse this instrument with a coolant temperature instrument, and sometimes label it as such. The probe to this instrument actually measures the temperature of the metal in your cylinder head. It allows you to monitor the proper operation of the liquid cooling system that cools your cylinder heads yet it does not measure the actual temperature of that liquid.
• Exhaust Gas Temperature (EGT)
  This instrument measures the temperature of your exhaust gases as they exit the combustion chamber and pass through the exhaust manifold. It offers an insight on combustion temperatures and allows you to monitor the quality of the air/fuel mixture. Too high a temperature would indicate a lean mixture, while too low would indicate a rich mixture. It may also reveal loss of compression in the cylinders.
• Fuel Pressure
  The fuel pressure instrument indicates the proper operation of your fuel pump and fuel supply system. It may reveal leaks, restrictions or a malfunction of the carburetor float valve system.
• Manifold Pressure
  This instrument offers an insight on how hard the engine is working. The more air/fuel mixture entering the engine, the higher the manifold pressure will be. It is particularly useful in setting the propeller pitch for optimal engine efficiency at different power settings. It may also reveal leaks in the intake system.
• Coolant temperature
  No provision for a coolant temperature probe is provided on Rotax 4-stroke engines and for good reason: the Cylinder Head Temperature instrument offers a better insight into the proper operation of the liquid cooling system and may reveal problems, such as the formation of air bubbles, that a coolant temperature instrument would not.
• Coolant pressure
  A coolant pressure probe may be installed, as it can help monitor the general operation of the cooling system and may reveal leaks and restrictions.
• Tachometer
  The tachometer measures the number of revolutions the engine performs per minute. It is useful in evaluating engine performance. For example, too low or too high a maximum engine speed at takeoff can reveal a problem. It is also useful in setting the propeller pitch to allow the engine to reach its optimal takeoff and cruise speeds.
• Hourmeter
  This instrument counts the number of hours your engine has been running. It is particularly useful in keeping a maintenance log!
• Aero Propulsion Technologies offers a full range of engine instruments