Electronics International US-8A - Manual (Page 16)

The Cylinder Head Temperatures are related to your engine’s ability to produce power. If any cylinder has a
problem producing power (fouled plug, burned or stuck valve, broken ring, intake leak, plugged injector,
timing problem, bad mag, etc.) the CHT for that cylinder will be abnormally high or low depending on the
extent of the problem. Each cylinder on your engine operates differently and has a normal operating tem-
perature of its own. The Ultimate Analyzer is capable of being programmed to match each cylinder on your
engine. When selecting the following limits, it is assumed your engine currently does not have a problem
and is operating properly.
A) Selecting the High CHT Limits: On a hot day with your engine set to 75% power, lean your
engine to peak EGT. Record the CHT readings for each cylinder with the cowl flaps closed. Program
the High Limit for each cylinder 40’F above the recorded reading for that cylinder.
Some aircraft reach the highest CHT temperatures during a long full throttle climb. If this is the case for
your aircraft, record the highest CHT readings for each cylinder during a long climb. Program the High
Limit for each cylinder 40’F above the recorded reading for that cylinder.
This High CHT Limit should not be set higher than the maximum limit allowed for your aircraft.
B) Selecting the Lower CHT Limits: The CHT Low Limits should be set to 150’F. Operating your
aircraft with CHT’s below 150’F is not recommended. The large difference between the combustion
temperatures and low CHT temperatures can cause engine damage. Setting the CHT’s to this low limit
allows you to place the Ultimate Analyzer in the Scan Mode during take-off without getting any warn-
ing lights. That way the Ultimate Analyzer can start analyzing your engine during the take-off roll.
C) Selecting the Shock-Cooling Limit: Lycoming recommends your CHT’s do not decrease more
than 1’F in 3 seconds. It has been E.I.’s experience this is a good number. Set your Shock-Cooling
Rate to 3 seconds for a 1’F change.
4. Oil Temperature:
As the oil passes through the engine, it is heated. It then passes through the oil cooler and reaches a stable
temperature, depending on internal engine temperatures, oil flow (pressure, etc.) and oil cooler efficiency
(airspeed, etc.). A change in any of these parameters will cause the oil temperature to increase or decrease.
With the 1’F resolution of the Ultimate Analyzer, oil temperature changes can be detected at a glance. This
allows the pilot to diagnose many problems that may never be noticed with a less sensitive gauge. Also, with
the 1’F resolution of the Ultimate Analyzer some of our customers are attempting to detect excessive wear in
the engine bearings.
Maintaining your oil temperatures within operating limits is essential. If the oil exceeds its maximum
operating temperature or if it is operated at excessively high temperatures for a long period of time, the oil
will break down and it will not possess the necessary lubricating properties to protect your engine. The
formula for long engine life is to change your oil at regular intervals and watch your oil temperatures with an
accurate gauge that can give you rate and trend information at a glance.
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Selecting the Proper Limits Operating Information