Question for Paul McBride, the General Aviation News engines expert: What is your professional opinion about flying a Mooney 20J with a Lycoming IO-360 engine lean of peak without fuel injectors if the temperatures are within guideline perimeters?
Paul’s Answer
This is a subject that has been around the general aviation community for a long time and it has always been a controversial topic. So, with that in mind, I’ll step off the cliff and give you my “professional opinion.”
Right out of the gate I’ll start off by saying that if it were my airplane and engine, I wouldn’t do it, and I’ll give you some reasons why.
Hopefully, anyone who is considering doing this during the operation of their Lycoming engine should first refer to Lycoming Service Instruction 1094D or its latest revision.
Probably the most important recommendation set forth in SI1094D is this statement in bold text: “ALL LEANING RECOMMENDATIONS ARE BASED ON CALIBRATED INSTRUMENTATION.”
Lycoming follows this statement by stating that the company also recommends “that all engine instrumentation be calibrated annually.”
Now I’ve been around the aviation community for a long time and I’ve got to be honest with you: I couldn’t tell you of one aircraft owner I’ve met over the years who has complied with that recommendation. How about you?
Another thing that really concerns me is that instrument calibration of the more sophisticated turbocharged engine is extremely important because of the higher operating temperatures.
While there are all kinds of products that claim better operational results — and there may be — I still am from the old school that subscribes to the aircraft and the engine manufacturers’ recommendations.
In my mind if these so-called improved operational products were that good, don’t you think the original manufacturer would be using them?
The one big question you must ask yourself is if these improved products are going to be suitable for safe operation across the board worldwide in some very different operational arenas than the one you operate in.
I’d also like you to think about one other thing: Is it worth it to operate your engine at lean of peak?
I think the two least expensive things you can put in your engine are avgas and oil.
If you don’t believe that, just ask someone who recently had to replace a cylinder.
