Question for Engine Expert Paul McBride: I changed out my avionics to an all new glass Garmin panel with 6 probe EGT and CHT.
My concern is the yellow on the CHT is now at 400, which I hit on takeoff and climb out. I have seen 408 before I pull back on power at full rich to bring them back down. I have no idea how high it would go.
The old panel never yelled at me or gave me warnings, so to see it hit 400 and then go yellow is unsettling.
Second question is about Lean Of Peak: I love the gas savings, but just pulling the throttle back only gives you “like” LOP at same performance.
But there is such a battle out there. Almost all mechanics I talk to say no to LOP.
Your view?
Jeff Traylor
Paul’s Answer: Jeff, I’m a bit at a loss here since you didn’t provide any specific engine or aircraft information, but I will answer your questions in a broad general manner. I think this should at least give you some guidelines and clear up some confusion that you obviously have since installing the new Garmin panel.
First, if you have a Lycoming normally aspirated engine, regardless if it has a carburetor or fuel injection and is 300 horsepower or less, I think it’s safe to say that the maximum continuous cylinder head temperature should not exceed 500° F.
Keeping the CHTs at 435° or below for continuous operation should give you the maximum service life of the engine.
I believe the new digital instrumentation is much more accurate than the old-style analog gauges, but I still wouldn’t be too concerned about the yellow if your CHT is below the 500° point.
This is where I always had a concern with the old analog gauges because most, if not all, were non-linear, which meant that a needle’s width at the bottom of the gauge may not have been the same as a needle’s width at the top of the gauge, leaving you not really knowing what the actual temperature was. This is why I still harp about gauge accuracy on older aircraft and the need for recalibration.
The bottom line: As long as you don’t exceed the 500° temperature during continuous operation, you shouldn’t need to be concerned. Ideally, keeping your CHTs between 385° and 435° would be just great.
With regard to running “lean of peak,” my only comment is that the two least expensive things you can put in your engine are gas and oil!
CHT’s in excess of 400 deg F for more than minute should be avoided and actions taken to reduce the CHT. Several things to check. Remember, aluminum loses half it’s strength at temps above 400deg, and your cylinder head is aluminum. I think Lycoming’s 500 deg F redline is ridiculously dangerous.
1) Are the engine baffles in good shape? Old tired baffling is a common problem for high CHTs
2) Is your fuel pressure set up properly. Get the engine manufacturers setup procedure for your engine and have your A&P verify that you are getting the correct fuel pressure either at the carb or fuel injection. Make sure the pressure is correct at idle as well as full RPM.
3) Is your mixture control set up properly; with red knob pushed all the way in, are you at the mixture full rich stop on the carb/fuel injector controller?
4) Make sure your CHT thermocouple connections are tight and correct per installation instructions from Garmin.
Paul,
That’s no answer for LOP! Tell us how you really feel about LOP from a technical point of view? I flew DC-6’s for United, we used LOP on every flight, as did the Air Corps, Air Force and Lindbergh. It helped us win a war!
LOP reduces CHT which is GOOD! Please give a real answer using your 40 years of knowledge at Lycoming,
The Lycoming Fuel Injected engines have a good induction system so that most of the time they will run LOP without the need for GAMI Injectors like Continenals.
Bob Gillette
Takeoff and climb to 1,000 AG at By. The cruise climb at higher speed. Reduce power after leveling off and IAS has reached desired speed. Then throttle back ( above 5,000 mal you can stay at full throttle ) ( Full throttle is richer with most carbs. )
Full thrott l e improves induction air flow. Lean the engine to 25° rich, then lean to save more fuel.
When descending the Garmin will remind you to richer.
Using carb heat riches so you might want to install a carb air temp. Carb ice is most often a warm weather high humidity problem since the venturi can cause a drop of temp to below freezing was to much fuel turns to a gas.
Winter time you get icing in the induction filter.
Does your Garmin show MAP?
The yellow and red “lines” (thresholds) on the Garmin G3x (and other EFIS, digital/programmable engine monitors, etc) are just software parameters that are set during configuration. In theory, they should have been set according to the same thresholds as the original gauge they replaced. If they new display doesn’t match those, it sounds like the avionics shop made a mistake during configuration that should be addressed. For safety sake, it’s probably (also) worth double checking other instruments, too, like the airspeed indicator to ensure those (think “white arc”, “green arc”, etc) reflect the appropriate values.