Why Your Engine Temperature Gauges Matter
Modern piston aircraft engines produce an enormous amount of heat every second they operate. Only a portion of the energy released during combustion is converted into useful power. The remainder must be managed and dissipated without damaging engine components. Two of the most valuable indicators of what’s happening inside your engine are Exhaust Gas Temperature (EGT) and Cylinder Head Temperature (CHT).
Although these gauges are often displayed side by side on modern engine monitors, they measure completely different things. Understanding the difference is essential for correct mixture management, diagnosing engine problems and operating your aircraft efficiently. Many pilots mistakenly believe that a high EGT automatically means the engine is overheating, or that reducing EGT is always beneficial. In reality, EGT and CHT tell different parts of the engine’s story, and interpreting them correctly provides valuable insight into combustion efficiency, engine health and operating technique.
This article explains what EGT and CHT measure, how they respond to mixture changes and why understanding both is one of the most valuable engine management skills a pilot can develop.
What is Exhaust Gas Temperature (EGT)?
Exhaust Gas Temperature is exactly what its name suggests—the temperature of the exhaust gases as they leave each cylinder.
An EGT probe is installed in the exhaust system a short distance from the exhaust valve, where it measures the temperature of the gases flowing past.
Unlike coolant temperature in a motor car, EGT is not a direct indication of engine temperature. Instead, it provides information about the combustion process itself.
Because the amount of fuel mixed with incoming air directly affects combustion, EGT changes significantly whenever the mixture is adjusted.
For this reason, EGT is primarily used as a mixture management tool rather than an engine cooling gauge.
What is Cylinder Head Temperature (CHT)?
Cylinder Head Temperature measures the temperature of the cylinder head itself rather than the exhaust gases.
A temperature sensor is usually installed beneath a spark plug or threaded directly into the cylinder head.
CHT reflects the amount of heat being absorbed by the engine’s metal components during combustion.
Unlike EGT, which responds almost immediately to mixture changes, CHT changes more slowly because it takes time for the metal to heat up or cool down.
For this reason, CHT is often considered the better indication of how much thermal stress the engine is experiencing.
EGT and CHT Measure Different Things
Although they’re closely related, EGT and CHT should never be considered interchangeable.
Exhaust Gas Temperature (EGT)
- Measures exhaust gas temperature
- Responds very quickly
- Primarily used for mixture adjustment
- Peaks near the ideal combustion ratio
- Not a direct indication of engine overheating
Cylinder Head Temperature (CHT)
- Measures cylinder head temperature
- Responds gradually
- Indicates engine thermal loading
- Generally lower when engine is operated correctly
- Primary indication of excessive engine heat
Think of EGT as telling you how combustion is occurring, while CHT tells you how the engine is coping with that combustion.
Why Does EGT Rise When Leaning?
As mixture is gradually leaned from Full Rich, combustion initially becomes more efficient.
Less excess fuel is available to absorb heat, allowing combustion temperatures to increase.
As a result, EGT rises steadily.
Eventually the engine reaches Peak EGT, where combustion is most complete.
Continuing to lean beyond this point reduces the amount of available fuel too far for maximum combustion temperatures to be maintained.
The combustion process becomes cooler and EGT begins falling again.
This creates the familiar EGT curve used for mixture management.
For a detailed explanation of Peak EGT, Rich of Peak and Lean of Peak operation, see our Understanding Aircraft Mixture Management guide.
Why Doesn't CHT Follow the Same Pattern?
One of the biggest misconceptions among pilots is assuming CHT behaves exactly like EGT.
It doesn’t!
Cylinder Head Temperature is influenced by several factors, including engine power, airspeed, cooling airflow, outside air temperature, engine baffling and mixture setting. This is why CHT does not simply mirror changes in EGT as the mixture is adjusted. While CHT often rises during leaning, it does not necessarily peak at exactly the same point as EGT.
In fact, the highest cylinder pressures, and therefore the greatest mechanical stress occur slightly Rich of Peak EGT. This region is commonly known as the Red Box and is generally avoided during cruise operation.
As the mixture is leaned further beyond Peak EGT into Lean of Peak operation, combustion temperatures and cylinder pressures reduce, often resulting in lower CHT despite continued engine operation.
This is why Peak EGT is not the hottest place for the engine.
Why CHT is Often the More Important Gauge
If forced to choose only one engine temperature indication, many experienced engine operators would choose CHT. That’s because excessive Cylinder Head Temperature directly affects engine longevity.
Persistently high CHT can contribute to:
- Increased cylinder wear
- Valve problems
- Cracked cylinder heads
- Reduced oil life
- Shorter engine life
Modern engine management places significant emphasis on monitoring CHT during climb and high-power operations. Keeping CHT within the manufacturer’s recommended limits helps maximise engine reliability and service life.
What happens during a mixture change
Imagine you’re cruising at 6,500 feet in a normally aspirated training aircraft. As you slowly lean the mixture, EGT begins to rise as combustion becomes more efficient, while CHT generally responds more gradually. Eventually EGT reaches its peak. If leaning continues beyond that point, EGT begins to fall again and CHT will typically stabilise before gradually reducing. If the aircraft and engine are approved and appropriately equipped for the technique, further leaning may result in Lean of Peak operation.
Multi-Probe Engine Monitors
Modern engine monitors can display the individual EGT and CHT of every cylinder alongside other useful information such as fuel flow, oil temperature and pressure, voltage and current. Having this information for each cylinder allows the pilot to see patterns that would be invisible on a traditional single-probe installation.
Differences between cylinders can help identify developing problems such as partially blocked injectors, failing spark plugs, uneven fuel distribution or cooling issues. Rather than simply knowing that “the engine” is hot or cold, the pilot can see how each cylinder is behaving.
Why One Cylinder Can Look Different
It’s perfectly normal for one cylinder to reach Peak EGT before the others. No two cylinders receive exactly the same fuel-air mixture.
Small differences in:
- Injector flow
- Induction airflow
- Cooling
- Manufacturer tolerances
mean each cylinder behaves slightly differently. Balanced fuel injectors reduce these differences, making Lean of Peak operation smoother and more practical.
What Causes High EGT?
High EGT alone is not necessarily a problem. It may simply indicate that the mixture has been leaned towards Peak EGT. Reduced fuel flow or differences in fuel distribution between cylinders can also produce higher readings. EGT becomes more useful diagnostically when considered alongside the behaviour of the other cylinders and other engine indications.
What Causes High CHT?
High CHT deserves closer attention because it reflects the temperature of the engine itself. Low airspeed during a climb, high outside air temperatures, excessive power, an inappropriate mixture setting, poor baffling or restricted cooling airflow can all contribute to elevated CHT. More serious combustion problems such as detonation or pre-ignition can also produce dangerously high cylinder temperatures.
Common Misunderstandings
"High EGT means my engine is overheating."
Not necessarily, EGT simply reflects combustion temperature and mixture position.
"Lower EGT is always better."
No, An excessively rich mixture may lower EGT while increasing fuel consumption and spark plug fouling.
"CHT and EGT always move together."
They often move in the same general direction but are measuring different aspects of engine operation.
"Peak EGT is the best place to cruise."
Generally no, Most manufacturers recommend operating comfortably Rich of Peak or, in appropriately equipped aircraft, Lean of Peak – not directly at Peak EGT.
Linking EGT and CHT to Mixture Management
Understanding EGT and CHT makes aircraft mixture management much easier to understand.
Rather than simply leaning until the engine runs rough, pilots equipped with engine instrumentation can identify where Peak EGT occurs and operate at the mixture setting recommended by the aircraft manufacturer.
At the same time, monitoring CHT helps ensure the engine remains within safe thermal limits.
Together, these two instruments provide a powerful insight into combustion efficiency, engine temperatures and overall engine health.
For a detailed explanation of how mixture affects EGT, CHT and engine performance, read our article Understanding Aircraft Mixture Management.
Conclusion
Exhaust Gas Temperature and Cylinder Head Temperature measure two different aspects of engine operation, but together they provide an invaluable window into what’s happening inside your engine.
EGT is primarily a tool for understanding and adjusting the fuel-air mixture, while CHT indicates how much heat the engine itself is absorbing. Learning how these two temperatures interact allows pilots to operate more efficiently, recognise developing problems earlier and better protect one of the aircraft’s most valuable components.
Whether flying a simple training aircraft or one equipped with a modern multi-cylinder engine monitor, understanding EGT and CHT helps transform engine management from following memorised procedures to understanding the reasons behind them.
Important Safety Reminder
Aircraft engines and operating procedures vary significantly. Always follow the Pilot’s Operating Handbook (POH) for the aircraft you are flying. Mixture management techniques that are appropriate for one engine may be unsuitable for another.
If you are unsure about leaning procedures, interpreting EGT or CHT indications, or how these principles apply to the aircraft you fly, speak with one of our flying instructors before attempting to apply them in flight. A short briefing can help prevent incorrect engine operation and improve both safety and confidence.
Feel free to call the club or email us via our Contact Us page.
