Six Probe Cylinder Head and EGT Gauge Use - Good
Lets begin with the aircraft engine. If you have a six cylinder engine you can, in normal flight at cruising speed, find the hottest running cylinder and, for safety back off 25 to 50 degrees.
Why is this so important? High temperatures, not controlled, can damage engine valves. If you can determine the hottest running cylinder using the two gauges above, and you back off 25 degrees on the cylinder that is the hottest running of the six (by testing each cylinder separately) you know for sure all the cylinders are running below the peak leaning point of the hottest running cylinder.
Why would you want to do this? An efficient leaning procedure, in aircraft at normal level flight and cruise speed, is attained by gradually leaning the engine until the RPMs decline a bit then enriching the mixture approximately 25 degrees. If you don't have a cylinder head temperature gauge this becomes a guessing game learned with experience. It will result in an engine that is running with near peak efficiency but you are not really sure.
Doing this, without a six probe gauge, may leave one or more cylinders above peak leaning temperature and make valve damage possible on those valves . This can occur after enriching the mixture 25 degrees. You really don't know, without testing, which cylinder is running the hottest when you lean them out together without testing each cylinder alone.
If you can find that hottest running cylinder,and you back off on the mixture control on that cylinder 25 degrees, you know the other cylinders are safe even though they may operate at a temperature cooler than the 25 degrees of the leanest cylinder. You are sacrificing a little efficiency for the longevity of the valves in the engine.
I will discuss the EGT in a future blog and combine the two in diagnostic procedures that could save you labor costs and part replacement costs.
