Q: I see 400° to 415° CHT on takeoff and 360° to 400° in cruise, depending on leaning, cowl flaps setting, etc. What’s acceptable on the O-540 Lycoming?
If I don’t lean much it’ll do 330-350, but that thing is thirsty running like this.
SCOTT HAMMACK
A: Scott, if you’re seeing 400° to 415°F during takeoff and 360° to 400° in cruise, you couldn’t ask for anything better, as long as you are confident in the accuracy of your instrumentation.
The maximum cylinder head temperature allowed for continuous operation on most of the Lycoming O-540 series engines is 500°F.
For best service life, from my personal experience, run the CHT between 380° and 400°.
If you have a six point CHT probe system, this would allow you to compare readings from all cylinders under different power settings. Of course the rule of thumb is when leaning, lean to the leanest cylinder.
The thing is, on a normally aspirated engine with a carburetor, the lean cylinder may be in a different cylinder depending on the specific power setting.
The reason for this, as I’ve mentioned in the past, is because the fuel distribution in an engine with a carburetor is poor at best and each cylinder is likely to be receiving a slight difference in the fuel/air ratio. The different lengths of the intake pipes contribute to this condition, unlike a fuel injected engine where a specific amount of fuel is delivered to each individual cylinder.
I think you are right in the ballpark with what you’ve got now and I see no reason to make any changes in your operating procedures.
I have a Lycoming 0-360 A1A in my 1952 Cessna 170 B. For my “Check List” I would like to print the following information. What is the best Oil temperatures for my engine, at cruise and maximum allowable?
What should my CHT temperatures be for cruise and maximum allowable?
Anything 400 deg F or higher CHT should not be accepted even in a carbeuatored engine. I would suspect that the baffles are worn out and leaking or just not installed properly.
Sometimes you can reduce MP about 1/2 inch, this clocks the throttle plate that increases air turbulence for better fuel atomization and improves distribution to the intake valves.