Hi there.
A little while ago, I had a flight with my IO-540 where one of my EGTs (#3) fluctuated significantly, between "normal" and a hundred degrees or more hotter than normal (CHTs were rock solid stable at the same temperatures they normally are). Hoping it might just be a EGT probe sensor problem, I swapped sensors between #1 and #3 to see if the problem followed the probe or the cylinder, but the result was inconclusive in that a subsequent test flight didn't see any temperature fluctuations at all. I since brought the sensors back to where they belong, in the process replacing the #3 sensor altogether with a new one. In the 4-5 hours of flying I've done since, I haven't seen any more fluctuations, so perhaps it was a sensor acting up after all; it's certainly what I am hoping it was.
But of course, I have to also consider the possibility it was a real issue, and it seems if it was, a sticking exhaust valve might have been the culprit. But I've seen very conflicting information on how to reduce the likelihood of a sticking exhaust valve. On the one hand, Lycoming recommends (in addition to frequent oil changes, air filter cleaning, etc., which I do) that the engine be operated at cooler temperatures, since excessive heat and hot spots may cause the formation of deposits:
https://www.lycoming.com/content/operational-and-maintenance-procedures-avoid-sticking-valves
Yet, Mike Busch, a well-respected engine expert seems to recommend exactly the opposite - that combustion temperatures be kept high (ideally with CHTs between 350-400):
https://resources.savvyaviation.com...ticles_aopa/AOPA_2020-07_why-valves-stick.pdf
Whose advice should I follow? I should also mention that traditionally, I have been running lean of peak (also on the advice of Mike Busch) and normally my CHTs are in the 320 range while in cruise flight. I'm not sure how I would actually increase CHT temperatures other than operating rich of peak or adding baffling... but on climb out in the summer, it's already a struggle to keep them below 400 unless I'm in quite a shallow climb.
Any advice?
Dan
A little while ago, I had a flight with my IO-540 where one of my EGTs (#3) fluctuated significantly, between "normal" and a hundred degrees or more hotter than normal (CHTs were rock solid stable at the same temperatures they normally are). Hoping it might just be a EGT probe sensor problem, I swapped sensors between #1 and #3 to see if the problem followed the probe or the cylinder, but the result was inconclusive in that a subsequent test flight didn't see any temperature fluctuations at all. I since brought the sensors back to where they belong, in the process replacing the #3 sensor altogether with a new one. In the 4-5 hours of flying I've done since, I haven't seen any more fluctuations, so perhaps it was a sensor acting up after all; it's certainly what I am hoping it was.
But of course, I have to also consider the possibility it was a real issue, and it seems if it was, a sticking exhaust valve might have been the culprit. But I've seen very conflicting information on how to reduce the likelihood of a sticking exhaust valve. On the one hand, Lycoming recommends (in addition to frequent oil changes, air filter cleaning, etc., which I do) that the engine be operated at cooler temperatures, since excessive heat and hot spots may cause the formation of deposits:
https://www.lycoming.com/content/operational-and-maintenance-procedures-avoid-sticking-valves
Yet, Mike Busch, a well-respected engine expert seems to recommend exactly the opposite - that combustion temperatures be kept high (ideally with CHTs between 350-400):
https://resources.savvyaviation.com...ticles_aopa/AOPA_2020-07_why-valves-stick.pdf
Whose advice should I follow? I should also mention that traditionally, I have been running lean of peak (also on the advice of Mike Busch) and normally my CHTs are in the 320 range while in cruise flight. I'm not sure how I would actually increase CHT temperatures other than operating rich of peak or adding baffling... but on climb out in the summer, it's already a struggle to keep them below 400 unless I'm in quite a shallow climb.
Any advice?
Dan