Hot Cylinder

The #1 cylinder on the O-470 in my 180 still runs above 400 during climb. The engine has 50 hours since major overhaul with new nickel cylinders. It is about 25 degrees hotter than the #3 next to it. It will get to about 410 during a 100 mph climb. #3 gets to about 385. I have checked and double checked the baffles (new from airforms) and they seem to be good.

Any helpful suggestions.

Do a differential compression check on #1 to learn if the exhaust valve is leaking. You could try just pulling the prop through by hand first to notice if one cylinder is a little softer than the others.

Does it even out in cruise or does it stay hotter?
What instrument? Maybe swap senders and see if it changes.
What's the ambient? You may benefit from cowl louvers.
How's your leaning authority in cruise and how does that cylinder react to leaning? Modern carbs are famous for being too lean.
Always check and double check your intake rubbers. Particularly at the Y pipe.

Wouldn't a leaky exhaust valve cause the EGT to run high. The EGT is actually lower on #1 than #3. #3 runs hottest.

skywagon8a said:

Do a differential compression check on #1 to learn if the exhaust valve is leaking. You could try just pulling the prop through by hand first to notice if one cylinder is a little softer than the others.

Click to expand...

Evens out in cruise. EI MVP-50. Ambient from 85 to 55 doesn't seems to matter much. I lean to #3 which runs hottest. #1 runs a little cooler. I have checked the rubbers.

I will take a photo of the display the next time I fly.

stewartb said:

Does it even out in cruise or does it stay hotter?
What instrument? Maybe swap senders and see if it changes.
What's the ambient? You may benefit from cowl louvers.
How's your leaning authority in cruise and how does that cylinder react to leaning? Modern carbs are famous for being too lean.
Always check and double check your intake rubbers. Particularly at the Y pipe.

Click to expand...

25* spread and 410* in climb wouldn't cause much worry for most owners. None in the pre-monitor era. If this was mine? I'd swap senders before anything else. And I'd still make sure I have 150* +/- spread between full rich and peak.

Haven't checked the spread. Is that to check jetting?

Yes. To establish you have adequate fuel flow to keep things cool during high power ops. My own plane used to run hot during climb and then stayed hot for a while after. More fuel flow solved the climb heat and subsequently my cruise temps are picture perfect.

If it hesitates or needs more fuel than normal at start up? Induction leak! Sometimes the leak will be more prevalent early in the flight and resolves itself when the engine warms up.

Them's my pireps. Good luck with yours.

Eddie Foy said:

I lean to #3 which runs hottest. #1 runs a little cooler.

Click to expand...

Carburetored Continentals can not be expected to have temperatures between cylinders close together due to the design of the induction system. Fuel injection engines can be expected to be close since the fuel enters the intake at the same relationship to each cylinder.

When you lean using an EGT analyzer on all cylinders as you have, you lean to the first cylinder which reaches peak and starts to cool. Then use that EGT to set the mixture rich of peak. Using lean of peak procedures is not recommended for carburetor engines. All of the other cylinders will be rich of peak. It matters not which cylinder has the hottest EGT. It is the first one which stops increasing. Is this the way you are leaning? If you are leaning by looking only at the hottest EGT you may be inadvertently placing your #1 CHT too high. I'm not implying that you may be leaning during climb.

Sometimes even with new baffles there can be a large air gap which allows cooling air to bypass a cylinder. Do your new cylinders have tapered fin diameters along the cylinder wall? The fin closest to the crankcase is the smallest diameter gradually increasing towards the cylinder head. If they do and your new baffles are designed for straight identical fin diameters, then with everything new you will have some large air gaps letting cooling air bypass the cylinder fins. If so these need to be closed.

Pete,
The MVP-50 tells you which cylinder reaches peak first. I run it in the digital mode. #3 peaks first. I am confident that the baffles are sealed well.

Is #5 your coolest? How about #6? Many of us have 5 completely shrouded and much of 6 blocked. I recall the shroud on 5 helping 3 and 1 but that was a long time ago.

I know it sounds simple but if the baffle rubber is blowing outwards at the right rear your problem is easy to solve. Lots of guys install the top cowl before the bottom just to make sure the baffles lay correctly.

Eddie Foy said:

The #1 cylinder on the O-470 in my 180 still runs above 400 during climb.... It will get to about 410 during a 100 mph climb......

Click to expand...

The O470 TCDS says 525 max with sparkplug gasket type probes, 460 max with bayonet type.
So even with bayonets, you're still 50 degrees below redline.

stewartb said:

Yes. To establish you have adequate fuel flow to keep things cool during high power ops. My own plane used to run hot during climb and then stayed hot for a while after. More fuel flow solved the climb heat and subsequently my cruise temps are picture perfect.

If it hesitates or needs more fuel than normal at start up? Induction leak! Sometimes the leak will be more prevalent early in the flight and resolves itself when the engine warms up.

Them's my pireps. Good luck with yours.

Click to expand...

You can run for over 100 hours in this condition before things start to come apart, then you end up spending lots of money.

Better to have extra fuel going in and leaning a bit than having limited fuel and end up lean on takeoff and climb.

hotrod180 said:

The O470 TCDS says 525 max with sparkplug gasket type probes, 460 max with bayonet type.
So even with bayonets, you're still 50 degrees below redline.

Click to expand...

While this is true, I have found that if you operate for long periods of time with the CHT over 400 you will be replacing cylinders. At least if you are on floats with long periods of time below 115 knots IAS producing inadequate cooling air flow.

stewart's suggestion of: "I know it sounds simple but if the baffle rubber is blowing outwards at the right rear your problem is easy to solve. Lots of guys install the top cowl before the bottom just to make sure the baffles lay correctly." is valid particularly with new baffle rubber. When you put on the top cowl look in there to be certain that the baffle is facing forward. You may need a flashlight to see it. I place the top cowl right side on first. Then I'm able to reach through the oil inspection door with my right hand to push the baffle forward.

I found that one cylinder was running 25 degrees hotter was doing so because the bushing to the rocker arm was offset and rubbing against the boss......creating extra friction heat....