Cylinder head temperature gauge wiring diagram for Westach, Westberg, CHT gauges.

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Cylinder head temperature gauge installation

 In order to allow for expansion of the piston in a two cylinder air cooled engine  the fit between the piston and the cylinder wall is such that it allows for this expansion. As the piston and cylinder heat under normal operating conditions they expand, the piston becomes "larger" while at the same time the cylinder walls expands making the bore smaller. Engine manufactures allow for this "expansion" and "contraction" when they produce the engine 

Normally a Rotax air cooled engine should read between 350F to 375F on a cylinder head temperature gauge (CHT) . When an engine overheats the amount of expansion between these parts is greater than allowed - the piston becomes too tight in the cylinder and the piston "seizes' creating permanent damage to the piston and or cylinder wall. 

A properly installed CHT gauge can alert the pilot to potential problems that may lead to engine seizure. 

CHT temperatures in excess of 40OF to 425F are a result of 

1. Lack of oil in fuel  or NO oil in the fuel.

2. Poor piston cylinder lubrication, due to poor quality of oil. For example using 10W30 motor oil instead of 2 stroke oil. 

4. The use of a fan belt other than that supplied by rotax, a loose, or damaged fan belt. 

5. A blocked fan intake duct, or blocked cylinder head fins. (for example from a mouse nest). 

 6. Insufficient cooling due to air intake  design. For example the fan being mounted right up against the firewall.

 7. Pre-ignition or detonation, caused by old fuel, improper octane, ignition timing. 

How does a CHT work ? - 

A CHT gauge uses a Type K thermocouple, which requires no power. The thermocouple  produces a small voltage  which to work properly requires  good continuity to reach the instrument 

The thermocouple, which is available in several different sizes depending on the spark plug used -  is mounted under the spark plug, and replaces the spark plug washer. All of the Rotax two cylinder aircraft engines use a 14mm probe.

On all two cylinder Rotax aircraft engines I would suggest a CHT for EACH cylinder to properly monitor the engine temperature.

On water cooled engines - 532/582 the cylinder head temperature will read about 200 degrees F., during normal operation. This is because the cylinder head is liquid cooled, and the probe is being effected by the additional cooling supplied by the liquid coolant. 

You might want to check out gauging your engine!

For a several web video interviews on how to properly gauge your Rotax aircraft engine subscribe to the Ultralight Flyer Web video magazine.

Cylinder head temperature gauge wiring diagram

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