Q: I have a Mattituck TMX O-360 in my Glastar. During a longer climb phase, my CHTs differ up to 100°F between Cylinder No. 1 and No. 4. Leveling off and reducing to cruise power (65%) at top of climb, CHTs stabilize all within max 30°F.
What could be the reason for this difference (airstream entering the cowl at a steeper climb angle?) and do I have to be concerned about this?
Christian Stuessi, Switzerland
A: Christian, thank you for submitting your question. I’m certain others who have engines equipped with a carburetor may have noticed similar cylinder head temperature differences, providing their engine has all cylinders equipped with CHT probes.
For a normally aspirated engine with a carburetor installed, it is not unusual to see this occur at different flight attitudes.
Most importantly, if the cylinder head temperatures are not reaching or exceeding the maximum allowed in accordance with the Lycoming Operator’s Manual, which is 500° Fahrenheit for your engine, or the specific limitations established by Mattituck in your case, I wouldn’t be too concerned.
There are a couple of things that may have an impact causing you to see a difference in CHTs.
First, I’d be looking very closely at the front cowl openings and what lies directly behind them. The location of the engine baffling and its condition have a direct impact as to how much ram air is allowed in and where it goes. It’s important to make certain nothing is allowing the incoming air to be mis-directed, resulting in higher CHTs.
Climb attitude certainly can be a factor, which might require a more shallow climb.
If the aircraft is equipped with cowl flaps, opening them may help in controlling the CHT difference.
I’m almost certain the Glastar does not have cowl flaps, so maybe making the mixture a bit richer would help also.
There is another factor that may be coming into the equation, which is the different lengths of the intake pipes on the engine. As I’ve mentioned many times before, the fuel distribution on an engine equipped with a carburetor is poor at best.
With the required fuel being metered at the carburetor on the bottom of the engine sump and with the different lengths of the intake pipes, the fuel/air mixture at each cylinder may not be identical and may cause a difference in cylinder head and exhaust gas temperatures readings.
You wouldn’t expect this on an engine that is fuel injected because each cylinder receives an identical amount of fuel. Should a difference in CHTs occur on that engine, I’d be thinking along the lines of a cowling/baffling problem causing the CHT to rise.
Christian, I don’t think you’ve got anything serious to be worried about, but I’d suggest a close visual inspection of the cowling/baffling on the right side of the engine looking at it from the pilot’s seat. It may be something as simple as a piece of baffling out of place, allowing the inlet air to be directed away from where it should be going.
One last thing that I would suggest, and that is to check with other Glastar owners operating an aircraft configured exactly like yours. It would be interesting to learn if anyone else, flying the same envelope as you, is experiencing the same condition.