Electronics International CA-1 - Manual (Page 10)

Operating Information
7
CHT's
It is not necessary to continually monitor the EGT’s in order to detect a problem. Most problems worsen
over a period of time and can be easily detected before they become a safety hazard by thoroughly checking
the EGT readings at run-up and once or twice during a flight.
CHT's
1. CHT Operation:
The Cylinder Head Temperature (CHT) instrument helps the pilot protect his engine against the threat of
excessive heat. Most general aviation aircraft monitor the hottest CHT, as determined by extensive flight
tests done by the airframe manufacture. Minimum in-flight CHT should be 150‘F, and maximum in most
direct drive normally aspirated Avco Lycoming engines is 500‘F. Some of the higher powered, more com-
plex engines have a limit of 475‘F. Although these are minimum and maximum limits, the pilot should
operate the engine at more reasonable temperatures in order to achieve the expected overhaul life of the
powerplant. It would be normal during all-year operations in climb and cruise to see cylinder head tempera-
tures in the range of 350‘F to 435‘F.
Sudden cooling of the CHT (known as shock cooling) is a problem that is common with aircraft engines.
This is caused by fast descents with little or no power and rich mixtures. This may result in bent pushrods
due to exhaust valves sticking, burned valves, spark plug fouling, broken piston rings, cracked cylinders at
the spark plug and valve ports and warped exhaust valves. To avoid these problems, do not allow the CHT to
cool more rapidly than 1‘F every 3 seconds during in-flight operation. This can be easily detected with our
1‘F digital display.
During climbs, the cylinder head temperatures will rise rapidly until the heat absorbed by the combustion
walls is dissipated out the engine’s cooling fins. At this point, the CHT will stabilize. Any change in
throttle, mixture, cowl or airspeed will affect the CHT and the rate at which it will change. Since rate and
trend information can be easily interpreted from our digital display, changing any one of these parameters to
stabilize, slow or reduce the CHT is possible with almost immediate results. Our digital instrument takes the
guesswork out of controlling your CHT.
2. CHT Diagnostics:
The source of heat in an engine is from the combustion of the fuel/air mixture producing temperatures of
approximately 4000‘F. Some of this heat energy goes into heating the cylinder heads through radiation and
conduction. This heat is sinked away from the engine by the air flow over the cylinder heads. When the heat
being generated in the cylinder heads equalizes with the heat being sinked away, the cylinder head tempera-
ture will stabilize. If a problem arises in the combustion chamber or in the ability of the cooling system to
sink away heat, the CHT’s will be affected. To detect a problem, become familiar with your engine’s CHT
operating temperatures during run-up, climb, cruise and descent. Any differences from normal can be a sign
of trouble.