Hi all -
I'm looking for ideas after battling a high CHT issue since August. We're stumped.
Background: Aircraft is a 1979 Warrior II with an O-320-D3G that I have owned for nearly 17 years. Engine was overhauled this past June by Penn Yan (they're local and my mechanic has a great relationship with them). As it turned out, the case and crank were non-serviceable, so I have what is essentially a new engine with the old data plate. Cylinders are new Lycoming nitride steel. I followed the break-in instructions provided by Penn Yan and ran it hard at continuous power over several flights while monitoring CHTs and oil consumption. Around 25-30 hours, oil consumption began to stabilize and CHTs came down to what I expected from the old engine (around 350-360 on the front cylinders, 370 on #4, and 380 on #3 -- historically the hottest). This was in July when ambient surface temperatures were above 90°F for much of the month. By all appearances, break-in was successfully completed and CHTs were seasonally consistent with the previous engine's summer performance.
Then cylinders #1 and #2 started running hotter than #3 and #4. #2 is the hottest, consistently 20-30°F hotter than #3 (the historical hottest). Even running at 65% power while full rich in cruise, it is very difficult to keep #2 below 400°F on a warm day. I have a JPI EDM-700 and can objectively review the data after each flight. I can see exactly when the front cylinders began running hotter than the back cylinders. It seems like something changed, but I cannot correlate the change with any mechanical intervention done on the airplane. So far, we have investigated:
Penn Yan has indicated that they're hearing anecdotal stories about high CHTs on engines with new Lycoming cylinders, but there's not much concrete data to go on there.
Does anyone have any suggestions?
I'm looking for ideas after battling a high CHT issue since August. We're stumped.
Background: Aircraft is a 1979 Warrior II with an O-320-D3G that I have owned for nearly 17 years. Engine was overhauled this past June by Penn Yan (they're local and my mechanic has a great relationship with them). As it turned out, the case and crank were non-serviceable, so I have what is essentially a new engine with the old data plate. Cylinders are new Lycoming nitride steel. I followed the break-in instructions provided by Penn Yan and ran it hard at continuous power over several flights while monitoring CHTs and oil consumption. Around 25-30 hours, oil consumption began to stabilize and CHTs came down to what I expected from the old engine (around 350-360 on the front cylinders, 370 on #4, and 380 on #3 -- historically the hottest). This was in July when ambient surface temperatures were above 90°F for much of the month. By all appearances, break-in was successfully completed and CHTs were seasonally consistent with the previous engine's summer performance.
Then cylinders #1 and #2 started running hotter than #3 and #4. #2 is the hottest, consistently 20-30°F hotter than #3 (the historical hottest). Even running at 65% power while full rich in cruise, it is very difficult to keep #2 below 400°F on a warm day. I have a JPI EDM-700 and can objectively review the data after each flight. I can see exactly when the front cylinders began running hotter than the back cylinders. It seems like something changed, but I cannot correlate the change with any mechanical intervention done on the airplane. So far, we have investigated:
- The carburetor (Penn Yan provided a new one under warranty, no impact)
- Timing (it's spot on)
- Baffles (they look good)
- We filled additional gaps with RTV and bolstered the baffles in a few places to ensure that they were not tucking under (into the airflow) or bending outward (with the airflow)
- They're the same baffles used with the previous engine
- Verified that the mixture goes all the way to the stop
- Looked for induction leaks at the individual intakes and at the carb (no evidence of leaks)
- Found a small induction leak on the #3 intake and replaced the gasket there
- Capped off the primer nozzles at each cylinder to ensure no air was leaking through the primer system
- Fuel pressure is good - that should not be limiting fuel flow
- I do not have fuel flow on the JPI, an oversight made 13 years ago that I sincerely regret today
Penn Yan has indicated that they're hearing anecdotal stories about high CHTs on engines with new Lycoming cylinders, but there's not much concrete data to go on there.
Does anyone have any suggestions?
