For those who only believe what manufacturers say...
From the Textron Lycoming article “‘Experts’ Are Everywhere to Help You” (their pub number SSP700):
... The newly discovered method of operating on the lean side of peak exhaust gas temperature has been known since Charles Lindbergh employed it to navigate the Atlantic Ocean and Max Conrad established distance records in his Comanche. This procedure was employed on large supercharged and turbocharged radial engines effectively during the era of large transport aircraft such as the Lockheed Constellation and Douglas D-6. ...
Lycoming is in complete agreement that it is possible to operate an engine on the lean side of peak TIT.[Bolding in the original.]. It is done on engines in our well-instrumented Experimental Test laboratory every day. There is nothing detrimental in operating an engine in this manner. ...
Having agreed that the facts are the facts - no other choice really, unless they wanted to look as stupid as some posters on PPRuNe - Lycoming went on to express this opinion: But you need proper instrumentation and GA pilots are too distracted doing other stuff to do it safely. Thousand of pilots flying aircraft with engine monitors and proper education have proved this
opinion to be wrong.
From the Continental Aircraft Engine Maintenance And Operator’s Manual for Models IO-550A, B, C and G, Form X30565 FAA Approved August 1990, para 13-2:
CRUISE CONTROL BY E.G.T.
If exhaust gas temperature indicator is used as an aid to leaning proceed as follows:
1. Adjust RPM for desired cruise setting
2. Slowly move mixture control toward “lean” while observing E.G.T. gage. Note position on the instrument where the needle “peaks” or starts to drop as mixture is leaned further.
3. The maximum recommended cruise setting is 235 BHP at 2500 RPM and 25.0 In. Hg. MAP with mixture set at 25F rich or lean of peak E.G.T. At cruise settings below 65% engine may be operated at peak E.G.T.
Although there’s a range of nonsensical aspects to that recommendation, I note that the recommendation includes a setting that dare not speak its name, with my bolding.
A Lycoming publication titled “More On Cylinder Head Temperature” says this:
Although [the specified temperatures] are minimum and maximum limits, the pilot should operate the engine at more reasonable temperatures in order to achieve the expected overhaul life of the powerplant. In our many years of building engines, the engines have benefited during continuous operation by keeping CHT below 400F in order to achieve best life and wear of the powerplant. In general, it would be normal all year operations, in climb and cruise to see head temperatures in the range of 350F to 435F.
Let’s assume the proposition that keeping CHT below 400F is good for engine longevity. At what mixture setting will CHT be
highest, all other variables unchanged:
1. 40F ROP.
2. Peak.
3. 40F LOP.
Answer: 1.
But maybe the manufacturers’ views on running engines LOP and the effects of temperature on engine longevity should be ignored, like the data?