CHT (cylinder head temperature)
Air cooled engines have a Ram air box which is installed (both sides) over the heads. The natural airflow over the heads, part of the cylinders and between the cooling fins cool down the head and the cylinder. The hot air escapes under the heads in the under cowling and further out of the cowling in free air. The way the ram airboxes are installed and the way and mass of natural air flow over the head is influenced by the installation and the speed of the plane. Because of that it’s not abnormal that different heads receive more or less flow against each other. Mostly the front cylinders receive more cooling thant the back cylinders. It means that cyl head temperature is not equal for all cylinders. For new, unproved installations /airboxes we strongly advise to measure CHT from all cylinders. Flight tests are required to find out if CHT’s are +/- equal ( a difference from up to 20°C is allowed.) and within limits. If the difference exceeds 20°C, modifications to the ram airboxes are required. Sometimes front cylinders need to be covered to avoid “overcooling”
EGT (exhaust gas temperature)
This is an excellent parameter to find out if the combustion in each cylinder is perfect. Every single damage such as a failed injector, a failed spark plug, a broken piston ring, a burned valve,….. will result immediately in an unsufficient combustion and thus a lower EGT. We recommend to monitor the EGT from all cylinder. It will give you an immediate indication of your engine's health.
