Higher CHT's on one cylinder

Stephen Shore

Stephen Shore

Pre-takeoff checklist
Joined
Sep 30, 2017
Messages
455
Location
Longview, TX
Display Name
sshore
Home Airfield
07F
New problem on my IO-540.

#1 Cylinder runs about 50 degrees hotter than the coolest cylinder CHT. #1 is the right front cylinder in a IO-540.

On climb I have to really manage it to keep it below 400 degrees CHT.

I have to run the engine LOP in order to keep the cylinder in the 360-375 degree range. Otherwise it quickly gets to 400 degrees.

Checked baffling, induction leaks, swapped probes, checked injector - all the easy stuff.

And this is really puzzling to me - on a descent with reduced MP, all other cylinders CHT declines (as would be expected) but this one cylinder quickly heads to 400 degrees on the descent.
 
Stephen Shore said:
swapped probes
Click to expand...
How much of a probw swap did you do? Physically swapped #1 and #3 probes, such that #1 temp would be indicated on #3? Otherwise you might still have a gremlin.

What are your EGTs doing?

How do the plugs look?

Have you confirmed in any other way (IR thermometer) that you are reading the actual CHT?
 
Swapped #1 and #3 probes. No change.

EGT looks normal. In fact the EGT delta is 36-38 degrees. #1 EGT is highest, but not by much.

I have NOT checked with an IR thermometer yet.
 
No A&P, here.

Last and worse cause would be a cam lobe going. A cylinder pressure thing. Especially if you’ve seen a gradual change and confirmed fuel, air, and cooling. But EGT doesn’t look different over time, does it?

Another avenue would be increased bore friction due to a broken ring or piston land. A quick and cheap scoping would rule that out; in a bad turnout the oil filter might hold clues to this.

Is your oil cooler on that side? Any increase in oil temp that would heat the air through the cooler affecting the cylinder? It’s not bug season up north, but that might be a far flung cause.
 
Can you share your CHT's on all 6 cylinders? I know you said you see a 50 degree delta to the coolest one, but I'd like to know the relative CHT's for each of the 5 others.

That said, have you checked the baffle wraps, the inter-cylinder baffles, the seals, etc? I know you said you checked the baffles, but depending on your POV, that could be anything from "Yep, they are still attached" to "I checked the wraps, the inner-cylinder baffling, the seals, etc with a flashlight in a dark hangar, filled any unnecessary gaps with RTV, and verified that the seals are making great contact everywhere they should".

Is there any history of this issue with other (presumably) Commander 114's?
 
The first thing to do is check the cooling baffelling, etc... around the affected cylinder.
 
455 Bravo Uniform said:
Last and worse cause would be a cam lobe going. A cylinder pressure thing.
Click to expand...

Yes, maybe. A buddy's Lyc O-360 had the up front cylinder running about 50 degrees hotter than the other 3. The engine gave an occasional stray miss on climb out, and the consensus was maybe the carburetor, or a little stray water in the fuel.

Nobody could figure it out until it suddenly started making lots of metal. Turns out it ate one cam lobe. Lots of metal was discovered after it ran hot for around 10-15 hours or so after the very occasional miss was noticed.

The owner is convinced his A&P failed to provide an adequate inspection of the oil filter during the last oil change. Operating hour-wise, the cam lobe seemed to deteriorate very quickly. Not sure his mechanic missed anything.
 
I don’t know how aviation cams are hardened, but if there is corrosion or excess wear, the hardened layer will be worn down to where it will erode more quickly (possibly in the hours between oil changes so that filter inspection might not catch it). Might be worth it to check the filter after you eliminate some other cheaper and easier diagnostics.
 
AV8R_87 said:
Why would a cylinder that's sucking in less air/fuel and producing less power run hotter?
Click to expand...
Depends which lobe is going away.

Exhaust valve, less heat shedding.

If intake valve and you go to LOP overall, then that one cyl w/less air will be closer to peak and be hotter than the rest.
 
AV8R_87 said:
Why would a cylinder that's sucking in less air/fuel and producing less power run hotter?
Click to expand...

That is the real head scratcher... it shouldn't be trending hotter if that cylinder is truly running LOP.

Initiating a descent without reducing MP or changing anything and see if that reduces or eliminates the rise in the #1 cylinder temp when the plane is pointed downwards without a power reduction? Maybe something changed and is disrupting the airflow that's related to the angle of the incoming air?
 
455 Bravo Uniform said:
I don’t know how aviation cams are hardened, but if there is corrosion or excess wear, the hardened layer will be worn down to where it will erode more quickly (possibly in the hours between oil changes so that filter inspection might not catch it).
Click to expand...
I've seen guidance that the time from initial pitting to the start of failure can be as little as 10 hours. I don't remember if that was a Lycoming or TCM bulletin, or some other document. But keep in mind filter checks and even oil analysis are limited in their scope and if the failure mode is outside those limitations your only option is if there are any operational changes. Not saying thats the case here, but any change from the normal is always a sign to look deeper and in a methodical manner.
 
Stephen Shore said:
New problem on my IO-540.

#1 Cylinder runs about 50 degrees hotter than the coolest cylinder CHT. #1 is the right front cylinder in a IO-540.

On climb I have to really manage it to keep it below 400 degrees CHT.

I have to run the engine LOP in order to keep the cylinder in the 360-375 degree range. Otherwise it quickly gets to 400 degrees.

Checked baffling, induction leaks, swapped probes, checked injector - all the easy stuff.

And this is really puzzling to me - on a descent with reduced MP, all other cylinders CHT declines (as would be expected) but this one cylinder quickly heads to 400 degrees on the descent.
Click to expand...

What did you recently do on the plane?
I agree with having some concern for this, but jeez, what does the manual say is safe?
 
4RNB said:
What did you recently do on the plane?
I agree with having some concern for this, but jeez, what does the manual say is safe?
Click to expand...
I get that....but after two years with a 21 degree delta on CHTs a 30+ degree increase on that delta makes me question what happened.

GAMI's do an amazing job - my EGT spread is still 24 degrees between hottest and coldest.

I have sent the engine analyzer data to GAMI for their opinion on why the CHT delta has increased so much and even more strange why the CHT on #1 rapidly increases on descent. No word back from them yet.

The oil analysis looks good - no sign of a broken compression ring. The bore scope on the cylinder does not show any problems either - no glazing or marks from a broken ring.
 
Stephen Shore said:
I get that....but after two years with a 21 degree delta on CHTs a 30+ degree increase on that delta makes me question what happened.

GAMI's do an amazing job - my EGT spread is still 24 degrees between hottest and coldest.

I have sent the engine analyzer data to GAMI for their opinion on why the CHT delta has increased so much and even more strange why the CHT on #1 rapidly increases on descent. No word back from them yet.

The oil analysis looks good - no sign of a broken compression ring. The bore scope on the cylinder does not show any problems either - no glazing or marks from a broken ring.
Click to expand...
George and John Paul should be able to point you in the right direction. I'm not sure how quick they will respond since they are currently up to their arse in alligators at the moment with the G1000UL concerns. Usually, higher cruise CHT points to a baffling issue but it should decrease in the same ratio on descent with reduced MAP. Regardless, it is a 'baffling' issue. FWIW, My 210 with a TSIO-520R has a problem child cylinder, #5, that is the right front located just behind the oil cooler. It is a known problem on many installations. The CHT on that cylinder is about 40F hotter than the rest in climb and about 30 more in cruise...but it tracks the same relative percentage on descent or if I pull back LOP (still the hottest by the same ratio). I have to run the boost pump in prolonged climbs in hot weather or full weight to keep it under 380-385. My EIS alarm is set to 390F but I do my best to mitigate the climbing temp if it tops 380. For me, 400F would require an immediate level off/power reduction/rectify the situation if the boost pump did not solve the issue. I wholeheartedly support your seeking a resolution and not accepting it regardless of the "acceptable CHT's" per the POH.
 
Again, I will ask, what had you recently done on the plane before this started?
 
You must log in or register to reply here.
Back
Top