A cylinder head temperature gauge is one of the most useful, and most misunderstood, readings on a dashboard or instrument panel. Drivers, riders and pilots often see a number and have no clear sense of whether it is normal or a warning sign. Forum threads are full of people comparing readings with no agreement on what counts as safe.
This guide clears up the confusion. It explains what cylinder head temperature actually measures, what a normal range looks like across cars, motorcycles and aircraft, and what to do if your reading looks too high.
Quick Answer
Cylinder head temperature, or CHT, measures the heat of the engine’s cylinder head directly, rather than the surrounding coolant. Normal ranges vary by vehicle type: around 90 to 105°C for most cars, 150 to 200°C for air-cooled motorcycles, and 190 to 220°C for piston aircraft engines. A reading that climbs steadily above these ranges, especially under normal load, is worth investigating.
What Is Cylinder Head Temperature (CHT)?
The cylinder head sits on top of the engine block and houses the valves, spark plugs and combustion chambers. It absorbs enormous heat during combustion, and its temperature is a direct indicator of how hard the engine is working and how effectively it is being cooled.
A CHT sensor measures this heat at the source, usually via a probe fitted directly into or onto the cylinder head. This makes it a more immediate and precise reading than coolant temperature, which measures the liquid that carries heat away rather than the metal generating it.
CHT vs Coolant Temperature vs EGT
These three readings are often confused, but each measures something different.
| Measurement | What it shows | Typical use |
|---|---|---|
| Cylinder Head Temperature (CHT) | Heat of the cylinder head metal itself | Aircraft engines, performance cars, motorcycles |
| Coolant Temperature | Heat of the liquid circulating through the cooling system | Standard road cars |
| Exhaust Gas Temperature (EGT) | Heat of gases leaving the combustion chamber | Turbocharged and diesel engines, performance tuning |
Coolant temperature is the reading most everyday drivers are familiar with, since it appears on almost every car dashboard. CHT and EGT are more specialised, appearing mainly in aircraft, motorcycles and performance vehicles where precise engine monitoring matters more.
Normal Cylinder Head Temperature by Vehicle Type
Because CHT is used across such different engine types, normal varies considerably depending on what you are driving or flying.
| Vehicle type | Typical normal CHT range | Notes |
|---|---|---|
| Petrol cars (liquid-cooled) | 90 to 105°C | Coolant-assisted, so ranges are lower and more stable |
| Air-cooled motorcycles | 150 to 200°C | No liquid cooling, so higher baseline temperatures are normal |
| Piston aircraft engines (e.g. Lycoming, Continental) | 190 to 220°C cruise | Sustained readings above 230°C are generally considered a concern |
These figures are general guidance rather than a substitute for your specific manufacturer’s data. Always check your vehicle or aircraft’s handbook for the exact range recommended by the manufacturer, since engine design and cooling method both affect what counts as normal.
How CHT Is Measured
CHT is measured using a thermocouple probe, either fitted under a spark plug washer, screwed directly into a threaded hole in the cylinder head, or clamped onto the head itself depending on the engine design. This probe sends a continuous signal to a gauge or digital display, showing real-time temperature rather than an average or delayed reading.
In cars and motorcycles, aftermarket monitoring tools can add a CHT gauge where one is not fitted as standard, often alongside other engine data such as boost pressure or air-fuel ratio. In aircraft, CHT gauges are typically a factory-standard part of the engine monitoring system, since precise temperature control is critical for engine longevity at altitude.
What Causes High Cylinder Head Temperature
Several common issues can push CHT above its normal range. Insufficient cooling airflow, whether from a failing fan, blocked radiator or restricted airflow around an air-cooled engine, is one of the most frequent causes. A lean fuel mixture, where the engine receives too little fuel relative to air, burns hotter and can raise CHT significantly. Ignition timing that is too far advanced can also increase cylinder head heat, as can sustained high engine load, such as climbing a long hill or maintaining high power output for an extended period.
In aircraft specifically, high density altitude and steep, sustained climbs are common contributors, since the engine works harder in thinner air while receiving less cooling airflow.
Signs Your CHT Is Too High
A gradual, steady climb in CHT during normal operation is the clearest warning sign, particularly if it continues to rise rather than levelling off. A sudden spike, especially paired with reduced power or rough running, suggests a more immediate problem. Persistent readings above your engine’s specified maximum, even if they eventually stabilise, should not be ignored, since sustained high heat accelerates wear on internal components.
What to Do If Your CHT Reading Is High
If you notice elevated CHT, the first step is to reduce engine load where safely possible, such as easing off a steep climb or reducing sustained high-power demand. Check that cooling airflow is not obstructed, including radiators, fans and air intakes depending on your vehicle type. If the reading remains high after reducing load, or if it climbs rapidly, it is worth having the cooling system, fuel mixture and ignition timing checked by someone familiar with your specific engine, since several different underlying causes can produce a similar symptom.
How CHT Affects Engine Performance and Longevity
Sustained high cylinder head temperatures accelerate wear on valves, piston rings and gaskets, and in more severe cases can lead to warping of the cylinder head itself. Consistently running within the normal range for your engine type is one of the simplest ways to protect long-term reliability, since heat-related wear tends to build up gradually rather than causing sudden failure. Monitoring CHT, rather than reacting only when a problem becomes obvious, allows smaller issues to be caught and corrected before they cause lasting damage.
Expert Insight
Engineers who work with CHT monitoring systems often stress that a single reading matters far less than the trend over time. A CHT of 210°C might be entirely normal during a hard climb in an aircraft, but concerning if it appears during gentle, level cruise. Understanding your own engine’s typical behaviour, rather than comparing directly against a generic number from an online forum, is the most reliable way to judge whether a reading is genuinely a problem.
Frequently Asked Questions
What causes high cylinder head temperature? Common causes include restricted cooling airflow, a lean fuel mixture, overly advanced ignition timing, and sustained high engine load. In aircraft, high density altitude and steep climbs are also frequent contributors.
How is CHT different from coolant temperature? CHT measures the heat of the cylinder head metal directly, while coolant temperature measures the liquid used to carry heat away from the engine. CHT tends to respond faster and gives a more direct picture of combustion heat.
What CHT is too hot for a car engine? For most liquid-cooled petrol cars, sustained readings above 115 to 120°C are generally considered a concern, though the exact threshold depends on the specific engine and manufacturer guidance.
Is a high CHT reading always a problem? Not necessarily. Short-term spikes during hard acceleration or steep climbs can be normal. A sustained, steadily climbing reading, or one that remains high during normal cruising or driving, is more likely to indicate an underlying issue.
How do I measure cylinder head temperature? CHT is measured using a thermocouple probe fitted to or into the cylinder head, connected to a dedicated gauge or digital display. Aircraft typically have this built in, while cars and motorcycles may need an aftermarket sensor added.
Quick Reference Table
| Vehicle type | Normal range | Concern threshold |
|---|---|---|
| Petrol cars (liquid-cooled) | 90 to 105°C | Above 115 to 120°C sustained |
| Air-cooled motorcycles | 150 to 200°C | Above 220°C sustained |
| Piston aircraft engines | 190 to 220°C cruise | Above 230°C sustained |
Understanding your specific engine’s normal CHT range, rather than relying on a single generic figure, is the most reliable way to catch a genuine problem early and keep your engine running well for years to come.
For more on keeping your vehicle running safely, see our guide to how long brake pads should last, signs, cost and maintenance tips.
