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"Cold Cylinder" 0-540

Geico266

Well Known Member
Ran into an interesting issue. Long story so I'll give you the short version.
#5 cylinder runs much cooler than the other 5. No engine monitor, just instrumentation on one cylinder. I just used a hand held infared. At idle the exhaust pipe is 350F, and all of the other cylinders are 650f - 750F. I found the issue when I changed plugs "massive to fine wire" and back. The plugs on #5 were noticeably cooler to the touch after a short run up. After flying hard for 20 mins #5 valve cover is 100f cooler than all the others.

Any ideas or thoughts would be greatly appreciated.
 
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Ran into an interesting issue. Long story so I'll give you the short version.
#5 cylinder runs much cooler than the other 5. No engine monitor, just instrumentation on one cylinder. I just used a hand held infared. At idle the exhaust pipe is 350F, and all of the other cylinders are 650f - 750F. I found the issue when I changed plugs "massive to fine wire" and back. The plugs on #5 were noticeably cooler to the touch after a short run up. After flying hard for 20 mins #5 valve cover is 100f cooler than all the others.

Any ideas or thoughts would be greatly appreciated.

One thing to try would be a flow rate test.
Pull all of the injector nozzles and reattach the to the lines. Put cups under the lines and then run the elect. pump.
Verify all cups have the same amount of fuel in them.
 
One thing to try would be a flow rate test.
Pull all of the injector nozzles and reattach the to the lines. Put cups under the lines and then run the elect. pump.
Verify all cups have the same amount of fuel in them.

That would be a good test for flow, but this is an 0-540.

I checked the sparks plug leads thinking one might be bad, but they both OHMed out okay. I know the plugs are good, I moved them and the condition stayed with the cylinder.

I did notice a lot of "blue" streaks coming from the rubber hose, and had a bad intake gasket. I've always thought an intake leak would run a cylinder hotter, not cooler?
 
Before I tried any adjustments I'd get a good engine monitor.

That would be a good idea, but I need to get this baby in the air. I could set up a temporary gauge to confirm my readings, but that wont fix the issue.
 
Am I correct in thinking an intake leak would cause cylinder temp and EGT to rise in that cylinder? :confused:
 
An interesting find. In this set up the #5 cylinder is the only one without a primer line. It has the post used for manifold pressure. Hmmmmm. Maybe the primer is leaking heating up the other 5 cylinders?
 
Am I correct in thinking an intake leak would cause cylinder temp and EGT to rise in that cylinder? :confused:

It depends on the size of the leak. If he leak is big enough, it would let so much air in that the EGT and CHT would drop.
 
Small intake leaks tend to have only a limited impact at high power settings and not likely to cause the heat delta's you are seeing. You should be able to visually see a significant leak source.

My next step would be a compression test on that cylinder. A likely scenario for your symptoms with no other noticeable problems (missing, rough running, itermittent behavior,etc.) is low compression (e.g. broken or stuck ring, sticking valve, chipped valve, etc.) The leak down test will confirm or exclude any compression issue and also tell you if it is a ring, intake or exhaust valve issue. When the fuel air charge is not fully compressed, the energy/heat produced during combustion is significantly less than when it is fully compressed. This could account for a significant reduction in head temps. The reduced power from the compromised cylinder is often not noticed on 6 or 8 cylinder engines until it gets bad enough to intermittently not fire.

Larry
 
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One common problem with Lycoming's are bad cams. An easy check is to remove the valve cover of the bad cylinder and the one next to it. With one set of plugs pulled turn the prop slowly and measure the lift on the rockers, bad cylinder and good cylinder. If they are obviously different you'll need to pull the cylinder and examine the cam lobes.
 
One common problem with Lycoming's are bad cams. An easy check is to remove the valve cover of the bad cylinder and the one next to it. With one set of plugs pulled turn the prop slowly and measure the lift on the rockers, bad cylinder and good cylinder. If they are obviously different you'll need to pull the cylinder and examine the cam lobes.

Good idea!
 
Well, I cleaned the primer (it was a little dirty), installed a new intake gasket, cleaned the threads in the spark plug holes and it runs like new. All temps are the same range now.


Thank you one and all for your input.
 
Small intake leaks tend to have only a limited impact at high power settings and not likely to cause the heat delta's you are seeing. You should be able to visually see a significant leak source.

My next step would be a compression test on that cylinder. A likely scenario for your symptoms with no other noticeable problems (missing, rough running, itermittent behavior,etc.) is low compression (e.g. broken or stuck ring, sticking valve, chipped valve, etc.) The leak down test will confirm or exclude any compression issue and also tell you if it is a ring, intake or exhaust valve issue. When the fuel air charge is not fully compressed, the energy/heat produced during combustion is significantly less than when it is fully compressed. This could account for a significant reduction in head temps. The reduced power from the compromised cylinder is often not noticed on 6 or 8 cylinder engines until it gets bad enough to intermittently not fire.

Larry

I forgot to mention I had done that first thing. It was 75/80.

Now that I have it running normal again it is MUCH smoother. I had allowed the roughness to become "normal" over time I guess.

Good input, thank you.
 
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