Since I added an engine monitor to the Lycoming O-360 in my Cherokee 180 a few years ago, I had noticed that the highest average and maximum cylinder head temperatures were unexpectedly on cylinder #2 (front left from cockpit perspective). I chalked this up to an anomaly in that particular engine. However, after recently replacing the engine with a factory-remanufactured one, cylinder #2 on the new engine also has the highest average CHT, by about 35 degrees F over cylinder #1 which is typically the lowest. For example, on a recent hour-long flight on a 90 degree day, the average CHT for the entire flight for #2 was 343, compared to 305 for #1, 317 for #3 and 322 for #4. The max temp for #2 was 390 compared to 346 for #1)
On a very hot day, CHT for #2 can go above 400 degrees on a vigorous climb-out after take-off, whereas none of the other cylinders do.
My mechanic has checked the baffling, and has checked for intake air leaks. We have replaced the CHT probe on cylinder #2 and checked its temperature with an infrared thermometer.
I know that CHT for #2 is within “normal” range as specified by Lycoming, but my concern is over the differences between cylinders and that I would have expected the front two cylinders to be the coolest given their location in the air flow.
In analyzing the situation, I have noticed:
Because of orientation of the cylinders in the engine case and the way piper designed the engine installation and cowling, numbers 2 has less fin area exposed on top to the air that enters the cowl as compared to cylinder #1 Could it be that #2 is more dependent on air that is forced underneath by the baffling, and thus the bottom of #2 is more dependent on air that has already absorbed some heat? (The CHT probe for each cylinder is below the lower spark plug)
My questions for other owners of similar airplanes who have engine monitors, or anyone with expertise in this area:
1) Is it normal for cylinder #2 to be hottest by 35 degrees?
2) Should I be concerned? (If I didn’t have an engine monitor I wouldn’t even know about this.)
On a very hot day, CHT for #2 can go above 400 degrees on a vigorous climb-out after take-off, whereas none of the other cylinders do.
My mechanic has checked the baffling, and has checked for intake air leaks. We have replaced the CHT probe on cylinder #2 and checked its temperature with an infrared thermometer.
I know that CHT for #2 is within “normal” range as specified by Lycoming, but my concern is over the differences between cylinders and that I would have expected the front two cylinders to be the coolest given their location in the air flow.
In analyzing the situation, I have noticed:
Because of orientation of the cylinders in the engine case and the way piper designed the engine installation and cowling, numbers 2 has less fin area exposed on top to the air that enters the cowl as compared to cylinder #1 Could it be that #2 is more dependent on air that is forced underneath by the baffling, and thus the bottom of #2 is more dependent on air that has already absorbed some heat? (The CHT probe for each cylinder is below the lower spark plug)
My questions for other owners of similar airplanes who have engine monitors, or anyone with expertise in this area:
1) Is it normal for cylinder #2 to be hottest by 35 degrees?
2) Should I be concerned? (If I didn’t have an engine monitor I wouldn’t even know about this.)
