High EGT

• CHT measures heat energy wasted during the power stroke, when the cylinder is under maximum stress from high internal pressures and temperatures.
• EGT measures heat energy wasted during the exhaust stroke when the cylinder is under relatively low stress.

High CHTs generally indicate that the engine is under excessive stress for its own good. That's why it's so important to manage the powerplant in a fashion that limits CHTs to a tolerable value. For Bonanzas and Barons, a reasonable rule-of-thumb is that optimum engine longevity is achieved by limiting CHTs to 380°F. CHTs above 400°F should be considered abusive, and grounds for "doing something right now" to bring them down.

By contrast, high EGTs do not indicate that the engine is under excessive stress. They simply indicate that a lot of energy from the fuel is being wasted out the exhaust pipe rather than being extracted in the form of mechanical energy sent to the propeller. High EGTs do not represent a threat to engine longevity. The engine is simply not capable of producing EGTs that are high enough to harm anything. Therefore, attempting to limit EGTs in an attempt to be kind to the engine is simply wrongheaded.

Troubleshooting using CHT and EGT

Having an engine monitor that displays and records CHT and EGT for each cylinder is also absolutely invaluable for detecting and diagnosing a wide variety of engine problems. The art of troubleshooting with an engine monitor is a subject that's so rich and fascinating that I'm in the process of writing a book about it. But to make a very long story short, here's a list of common engine problems and how they show up in CHT and EGT:

• Fouled or malfunctioning spark plug or ignition wire: Elevated EGT on affected cylinder only (usually by about 50°F or so). Slightly reduced CHT on affected cylinder. Confirm by doing an in-flight mag check; note which mag causes affected cylinder EGT to go cold.
• Malfunctioning magneto: Elevated EGT on all cylinders (usually about 50°F or so). Slightly reduced CHT on all cylinders. Consider confirming by doing an in-flight mag check, but be careful - if you turn off a mag and the engine quits, pull the mixture control before turning the mag back on to avoid possible afterfire-damage to the exhaust system.
• Partially clogged fuel injector: If ROP mixture, elevated EGT and CHT on affected cylinder. If LOP mixture, reduced EGT and CHT on affected cylinder, and possible engine roughness.
• Completely clogged fuel injector: Engine rough, EGT cold, CHT dropping. Attempt to unclog by going to full-rich mixture and high boost; otherwise, land as soon as practicable.
• Burned exhaust valve: Slightly elevated EGT on affected cylinder only (usually by about 20°F to 60°F, depending on how badly the valve is burned). EGT usually varies between normal and slightly elevated, often (but not always) in a rhythmic fashion with a frequency of roughly one or two cycles per minute. (If burned valve fails completely, EGT of affected cylinder will go cold and engine will run rough.)

Incorrect....and saying it in all CAPS does not change that.

CHT is a good measure in an aircooled engine, it is a poor measure in a water cooled head engine. EGT can see changes quickly CHT is very slow...again in a water cooled engine.

Horses for courses.

Please Please do not use Air cooled engine articles and rules in a ROTAX engine..this is misleading.

I agree. CHT's in a water cooled engine read way slower than an EGT. EGT would  something going on way before a CHT would. They can be used in conjunction with each other like all the readings.