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High Cylinder Head Temp

N999BT

Well Known Member
Patron
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.
 
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
 
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.
 
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.
 
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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.
 
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
 
Email Sent

Robert,
To minimize thread drift I will send you an email addressing your points and bring you up to date on my situation.
 
High CHTs

Since you have the Lightspeed EI, I would recommend checking your ignition timing using a strobe light. The instructions are in the LSE manual. One potential reason for high CHTs is a failed pressure transducer (for manifold pressure input) in your LSE brain box and this check would reveal that.
 
Most likely an intake gasket leak. If running ROP the EGT will be a bit higher and the CHT higher.

Things like a broken ring or similar can do the same thing so look inside if you can with a borescope. This is far less likely but you would not be the first.
 
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.

If the EFII installation included a conversion from Mags to EFI, that is your CHT issue. As the MAP decreases in your climb, the timing advances. This advanced timing will increase your CHTs. I have EFI and the only time I hit 400* is when I am at the end of a climb to 8 or 10K (didn't happen with Mags). I would guess the EFII units start getting aggressive around 23-24" You can look for a correlation between the CHTs and the MAP.

Larry
 
Most likely an intake gasket leak. If running ROP the EGT will be a bit higher and the CHT higher.

Things like a broken ring or similar can do the same thing so look inside if you can with a borescope. This is far less likely but you would not be the first.

Assuming the OP is at higher alttitudes while cruising, he is probably WOT and therefore no meaningfull vacuum in the induction system. Induction leaks have only a small effect on delivered mixture when WOT.

Larry
 
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.

About the only thing that will signficantly affect CHT's is combustion temps and total cooling. oil burns just like gas and will have no significant impact on CHT. Friction usually heats the cylinder and not the head. Some of that heat makes it to the head, but not typically enough to produce the numbers you are seeing (50* delta). You should focus on three things that substantially affect CHT: 1) mixture (difficult for varying mixture to produce a 50* delta though) 2) timing and 3) cooling. It is also possible that you are getting mild detonation. This will increase your CHTs and would be otherwise undetectable in our noisy cockpits. Oil burning leaves carbon deposits and those deposits can cause pre-ignition. Most of the deposits are below the ring, but it can produce deposits in the combustion chamber. As others mentioned a borescope inspection is definitely warrented here.
 
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Update

Did a compression test cold. Cylinders 1 2 and 4 were all mid 70/80, number 3 was 55/80. Decided to start the engine and warm it up to see if the problem went away. I let it idle for about 10 minutes, and then decided to start increasing rpm slowly. At about 1100 rpm there was a rapping sound coming from the engine. My mechanic buddy got up there and put his hand on the valve cover of number 3 and could actually feel the knock.

We suspect a stuck exhaust valve.

Then we shut it down, took it in the hanger and did a warm compression test. No significant change. While on number 3 (the hot cylinder) we rocked the prop back and forth a few degrees (maybe 10 to 15) to try to increase the reading. There was a definite leak out the exhaust valve. Also, on one of the rocks the pressure in the cylinder would release out the breather.

Decided we would have to take the cylinder off and have a good look. We took all the cylinders off, number 3 had a different colored exhaust valve than the others and a stuck top compression ring. Also, the top ring was not contacting the cylinder wall for about 1.5 inches straddling the split line.

Sooo, I think the CHT problem was caused by blowby, possibly accentuated by leaky exhaust valve. Anyway, I'm shipping all the cylinders off to Lycon have them looked at. I'll update if they find anything else.
 
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