2024 SR22 NA, IO-550-N, Perspective data on every flight. Since April, #4 has run 35 to 65F hotter than the median of the other five in every phase. Hits 420 in a normal full rich climb on hot days. Low utilization airplane.
What we’ve done and ruled out:
CHT probes verified with a heat source and swapped to other cylinders. Reading follows the cylinder, not the probe. Not instrumentation.
Takeoff fuel flow 27.5 to 28.3 GPH on every logged flight, in spec per SID97-3.
EGTs are level across all six when leaning, #4 actually runs the lowest EGT. No lean cylinder signature, so not an injector or induction leak.
Found ring blow by on the original #4 (pressurized the cylinder, steam and air out the dipstick tube). Replaced it with an overhauled cylinder. That fixed part of it. Ground running delta went from +14 to basically zero. But in flight the offset is still there.
Baffling inspected repeatedly, cowl off. Seal strips oriented into the pressure side, inter cylinder baffles in place, old RTV from a previous shop experiment removed. Everything looks right on the bench.
Here’s the part that has my attention. With the new cylinder, the offset only exists in flight and it grows with airspeed. Taxi, +3. Climb at 113 knots, +42. Cruise at 144 knots, +49. Descent, +36. Back on the ground it collapses to normal within two minutes. Power setting doesn’t drive it, airspeed does. Reads like a cooling air distribution problem that only shows up under flight plenum pressure, meaning the cowl on condition, which we can’t see during inspection.
Question for the group: has anyone chased this specific pattern on an SR22 and found the culprit? Is there a known seal, cowl ramp, or baffle detail at the #4 position on these airframes that folds or lifts with the cowl on and looks perfect with it off? Would rather learn from someone’s scar tissue than keep pulling the cowl.
Happy to post the CSV data if useful.