Doug Rohrer
Well Known Member
I have a major CHT problem with my #3 cylinder that has me "baffled" so I am asking for advice. Problem is getting worse with the hot weather here.
Two year old RV-9A with O-320-D2B 160HP rebuilt engine. Engine was built with all new Lycoming cylinders. Plane has about 140 hours total time. Dual Pmags timed at 2* ATDC. Garmin G3X panel. Catto fix pitch prop.
On climb out, #3 heats up fast and run as much as 100* hotter than the other cylinders. EGT is 150* hotter than the average of the other cylinders as well. I have to stay below 200-300 fpm climb to keep #3 below 425*. Oil temps are fine at 190*. Oil cooler is mounted on the firewall and gets air through a 4" duct behind #4. Even with all this air diverted from #4, it runs relatively cool. These is no air dam in front of #1 and there is a stock full height air dam in front of #2. Any air dam in front of #1 only makes the problem worse. Fuel flow is 13.5 GPH at full rich during climb.
Here is the kicker: once at cruising altitude, all the CHT's level out and #3 is slightly cooler than the other cylinders. If #3 had a vacuum leak, it seems it would be worse at cruise than during climb out.
My baffles fit well and all gaps and holes are sealed. The inlet ramps are sealed internally. I have tried the washer trick between the rear baffle and #3 cylinder, but it seems to make no difference. There are no fins near the screw anyway.
One other piece of info that may or may not be relevant: I have 78/80 compressions on #1,2 and 4, but only 70-72/80 on #3. I has been this way since new. Air leakage during the test seems to come out the crankcase, so it is getting past the rings. I don't see how this would affect my heating issue, but it is suspicious, no?
Has anyone tried to duct air transversely across the top of the engine? Would the ASA electric shutter system solve this problem?
Any suggestions would be appreciated.
Two year old RV-9A with O-320-D2B 160HP rebuilt engine. Engine was built with all new Lycoming cylinders. Plane has about 140 hours total time. Dual Pmags timed at 2* ATDC. Garmin G3X panel. Catto fix pitch prop.
On climb out, #3 heats up fast and run as much as 100* hotter than the other cylinders. EGT is 150* hotter than the average of the other cylinders as well. I have to stay below 200-300 fpm climb to keep #3 below 425*. Oil temps are fine at 190*. Oil cooler is mounted on the firewall and gets air through a 4" duct behind #4. Even with all this air diverted from #4, it runs relatively cool. These is no air dam in front of #1 and there is a stock full height air dam in front of #2. Any air dam in front of #1 only makes the problem worse. Fuel flow is 13.5 GPH at full rich during climb.
Here is the kicker: once at cruising altitude, all the CHT's level out and #3 is slightly cooler than the other cylinders. If #3 had a vacuum leak, it seems it would be worse at cruise than during climb out.
My baffles fit well and all gaps and holes are sealed. The inlet ramps are sealed internally. I have tried the washer trick between the rear baffle and #3 cylinder, but it seems to make no difference. There are no fins near the screw anyway.
One other piece of info that may or may not be relevant: I have 78/80 compressions on #1,2 and 4, but only 70-72/80 on #3. I has been this way since new. Air leakage during the test seems to come out the crankcase, so it is getting past the rings. I don't see how this would affect my heating issue, but it is suspicious, no?
Has anyone tried to duct air transversely across the top of the engine? Would the ASA electric shutter system solve this problem?
Any suggestions would be appreciated.