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High Cylinder Head Temp
I have a carbureted Lyc O-360 in my plane, top plugs are lightspeed EI and the lowers are Bendix Mag. Typically in cruise my CHT's are 360 +/- 10 degrees F. The engine has about 800 hours since the last overhaul, and has superior power units (cylinder, piston, head). On a hot day, running all out (racing) my CHT's may reach 410F or so, but are all fairly even.
About a month ago, the number 3 cylinder spiked a above the others by 30 to 50F, so it might hit 430F in a climb, and with the others maxing out at about 375-380F. After getting to cruise speed, it would go to 360F on the other 3, and be difficult to keep the number 3 below 400F. Coincidently with all this, I changed my crankcase breather line routing, and now I am going through a lot of oil. I suspect the new routing, but it could be related to other stuff going on in the engine, none of it good. I think a lot of it is going out the breather because I now am having oil dripping off my airplane that I did not have before. I plan to add in a separator, but if something is seriously wrong with number 3, I need to solve that first. Any advice on diagnosing the problem would be appreciated. |
Might be time for a borescope through the spark plug hole.
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Check the cht probes first. Swap the probe/cylinders assignment and see if the hot cylinder moves. Or better calibrate all 4 in boiling water or hot oil.
I *think* where you locate the case vent and the local pressure there can affect how much oil goes overboard. Put it back maybe and see if the problem goes away. I agree a borescope would be a good idea also. Just speculation but I wonder if you have a cylinder pumping oil and it's burning that oil if it could send the cht up. Tim |
First things first swap the CHT probe to another cylinder and see if the problem follows it.
Chris |
I did swap probes
I swapped no 1 and no 3, no change. It could be my harness, because the no 3 harness can't get to the no 1 position, but I did swap probes.
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As others have hinted you may have an issue with the barrel, check the plugs, and do a leak down and borescope inspection. You should consider that the oil usage and blow-by could be from a bad cylinder, if we have all the information. Higher friction could be the cause of CHT increase. Nothing is for sure, though!
Exhaust valve sticking? Maybe but not related to blow-by change. |
What are you running mixture-wise in cruise? ROP or LOP? If you run Rich, and the #3 has an induction leak, it will be closer to peak than the others, and thus hotter. However, if you normally run LOP, then it woudl still be leaner - which woudl mean cooler.
Uneven distribution is at least one thing to look at, and could be as simple as an induction tube seal or gasket. Paul |
ROP Mostly
I do run ROP most of the time. Usually if I am going somewhere I fly pretty high, so usually I just lean until it sounds right then richen a hair. Almost always this is higher than 8500 msl because mountains in every direction.
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Timely Post
I know there are a bunch of previous post regarding CHT.
This one is more along the lines of my problem. Things just "magically" change with no apparent reasoning. I have an IO-320 with EFII. At 75 hours I had gotten fed up with the original FI system from Lycoming and converted to EFII. That sure improved the mixture problems I was experiencing. However, the CHTs were all in line with what I had experienced from day 1. Now at about 100 hours on the engine, with no physical / mechanical changes my # 2, 3, 4 CHT shoot up to 430+ on climb out. Yesterday I took the plane to Synergy Air (KEUG) and worked with Ryan replacing all my baffle material with the AC "textured" ⅛" x 3" x 9' baffling. Beautiful work... BUT, my CHT still climb above 420... I'm at a loss as to why - with no physical / mechanical change the CHT would start climbing much higher than prior to 100 hours (320 ~ 360). Looking forward to seeing what comes in response to the OP thread as it may help my troubleshooting. |
CHT change
Hi Mel,
Something changed. Are you climbing slower? Are your EGTs different. Is your air fuel ratio any different? Is it 40 degree hotter outside than it was? Is your oil temp different than before? Are your (EFII) MAP sensors reading correctly? There is always a reason for any change. Look for a little more data or a clue to follow. Robert |
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