CHT Sensor Guide

AiM CHT (Cylinder Head Temperature) Sensor Guide

This guide explains how to interpret an AiM CHT channel using MyChron 5 or MyChron 6 data for kart racing in New Zealand. MyChron 5 is obsolete and no longer sold by Harris Race Radios; parts, sensors, repairs and existing-owner support continue. MyChron 6 models are the current new-unit range.

What the CHT sensor measures

An under-plug CHT sensor measures temperature at its installation point near the spark plug. The sensor, washer dimensions, connector, cable and supported input must match the engine and exact MyChron generation. It is a different measurement from coolant temperature or exhaust-gas temperature.

  • Monitor cylinder-head temperature trends on a compatible engine installation.
  • Compare readings under similar load, ambient conditions and sensor placement.
  • Investigate abnormal behaviour using engine checks and other available data.

Why CHT matters

CHT can help monitor engine behaviour over time, particularly on applications where head-temperature monitoring is specified. It does not directly measure mixture strength, prove detonation or guarantee protection from overheating.

Engine-specific CHT ranges and alarms

Use the normal operating range, warning threshold and stop limit specified by the engine manufacturer or engine builder for the exact engine, kart class and sensor installation. Do not apply one Briggs, Yamaha KT100 or Vortex range to every configuration. No universal numerical CHT target is prescribed here.

Set the MyChron alarm to the verified application value, with the correct units and channel function. The sensor's measurement range or operating limit is not an engine safety limit.

How to read CHT data

Use the Race Studio 3 workflow to compare the channel with lap position, engine load and conditions:

  • Warm-up: compare the rise with the exact engine's warm-up requirements.
  • Stable phase: confirm that the reading remains within the verified engine-specific range; a smooth trace can still be outside it.
  • Sudden change: investigate the engine and the sensor installation, connection and configuration before attributing it to one cause.
  • Session comparison: account for weather, load, fuel and any change in plug or sensor fitting.

Common CHT symptoms and checks

Symptom Possible causes to investigate First check and stopping point
Above the verified engine limit Engine or cooling problem, abnormal conditions, sensor installation or configuration Stop safely and consult the engine builder's procedure. Do not keep testing to obtain more data.
Lower than expected Load and ambient conditions, sensor contact, channel assignment or wiring Verify the measurement before drawing tuning conclusions.
Erratic values or sudden spikes Sensor damage, connection fault, interference or actual engine-temperature change Inspect externally when safe. Follow the specified plug/sensor fitting procedure; do not simply tighten the plug harder.

Using CHT during tuning

A high CHT reading does not by itself prove lean jetting, and a low reading does not prove rich jetting. Do not make a jet change from this channel alone. Follow the exact engine builder's procedure and compare other evidence. CHT and EGT measure different things; neither is universally more reliable for every engine and installation.

Maintenance and measurement reliability

  • Follow the engine manufacturer's and sensor's fitting instructions for the under-plug washer arrangement and plug tightening.
  • Inspect the sensor washer and lead for damage when safe.
  • Route wiring away from exhaust heat, abrasion and ignition interference.
  • Check cooling shrouds and ducts as required by the engine maker.
  • Stop testing and contact the engine builder or Harris Race Radios if engine distress, an installation problem or unexplained readings persist.

Related guides

← Back to AiM MyChron Knowledge Hub