Low EGT at power

[edstepec]

I need to ask the forum if I have an issue here. I have 3 photos attached showing CHT/EGT with #4 cylinder having unusual readings. The engine is a o320 150hp. At full power, the EGT is unusually low 1159 and 349 CHT. At cruise power, EGT is closer to other 3 cylinders as well as the CHT. At low power settings, all temps are close to each other. Full power settings in climb is where the temperature gaps are at the highest. All the variables are on the photos and looking for guidance or is this behavior normal?

 

[bjdecker]

EGTs

EGT is just a number.

It's only useful when you compare it and its cohorts over time to each other, during a magneto check, or when you compare its behavior, along with its cohorts, to fuel flow (find lean of peak, find rich/lean cylinder-injector)

The location of the EGT probe, with respect to the exhaust port, will greatly effect its readings -- the closer to the port, the higher the temperature.

The last picture that shows the relatively lo CHT and lo EGT with an RPM of 2270 and a MAP of 28.2, is >NOT< full power. It does show that the #4 cylinder is getting rich -- probably from the weird airflow induced by the low airspeed and wide open throttle causing more fuel and less air to make it up the induction. Just a guess...

I know I'll get yelled at for this analogy - but I like to think of it like a car with a standard 5 speed transmission. At the line, you start off in 1st gear and press on the gas pedal, no problem. If you start off the line in a high gear (3rd - 5th), the engine bogs down and the car doesn't go anywhere. This is what happens with the propeller pulled back (2270RPM) and the throttle is wide open (28.2").

Look at your fuel flow to help determine "power"

 

[oaklandaviator]

Carbs

Carburetors don’t do a great job of getting even mixture distributions to all cylinders. Before all the fancy instrumentation you’d have maybe a CHT and oil temperature gauge and possibly a single EGT. If it runs smoothly and all the CHTs are in the green I’d think all is well. If your engine was injected, then that changes things completely.

 

[sailvi767]

I would personally be a bit more concerned about the EGT’s on 1 and 2 if the full power picture is also with the mixture full rich. As others mentioned EGT is more of a relative measurement but from full rich to peak EGT you should have at least a 150 degree range. If you are leaned in the climb disregard.

 

[lr172]

Pretty typical for a Lyc carb'ed engine. At WOT, 3&4 get a different distribution of fuel. #4 is VERY rich (CHTs drop along with power when too rich) and hence the readings. 3 is also rich, but not as bad as 4. 1&2 are seeing more normal mixture and in fact probably on the lean side for WOT. This is just the poor design. the fact that all lines up in cruise and mid power shows no major problems beyond the design flaw.

Larry

 

[johnpaul44]

I have this exact problem as well on my carb RV6 but with the O-360. Throttling back about 1inch or so once i reach pattern alt seems to bring all the egt very close to each other, within 50-degree spread. At full throttle they are closer to 150 degree spread

 

[Marlonyoung]

Try fiddling with small applications of carb heat, especially in cruise. Sometimes that can change airflow patterns and distribution to bring EGT closer together. Helps on my O320 RV4. On the C195, we routinely fly with 80 to 100 degrees carb heat for a similar issue.

 

[edstepec]

Thank you all for your most valuable inputs. Really appreciated. Yesterdays flight was most interesting, by pulling pack the throttle from full power to maybe just a 1/4 inch, no RPM reduction, the EGT temps for 1&2, swapped to 3&4. It was an immediate change in temperatures. 1&2 were now low with 3&4 high. Almost an identical swap. Again no RPM drop and my thought, find the throttle position where EGT temps are balanced and adjust the throttle stop on carb? Thoughts?

 

[alpinelakespilot2000]

Thank you all for your most valuable inputs. Really appreciated. Yesterdays flight was most interesting, by pulling pack the throttle from full power to maybe just a 1/4 inch, no RPM reduction, the EGT temps for 1&2, swapped to 3&4. It was an immediate change in temperatures. 1&2 were now low with 3&4 high. Almost an identical swap. Again no RPM drop and my thought, find the throttle position where EGT temps are balanced and adjust the throttle stop on carb? Thoughts?

See post #2 above. The EGT values by themselves are meaningless. There is no value to making them all equal because their differences have as much to do with location of the probes as anything else. At most, you only need to monitor their relative value to each other to see if anything changes from flight to flight, or use each EGT individually to find each cylinder's peak for leaning purposes.

In short, monitor your CHT's to keep them within their appropriate ranges and don't waste time chasing EGT's.