I have a new-to-me 1976 180J with a mid time PPonk. Very difficult, and nearly impossible on floats, to keep the #5 CHT under 400 degrees. Yesterday coming back from the Priest Lake Splash-in I could only keep it under 400 degrees with 16 gph at 22"sq in cruise. At about a 90kt, full-throttle, full-rich climb it was 417. Half fuel, just me and 50 lbs or so of stuff. Ambient temp about 70 degrees at 4500 msl.

The previous owner (who did disclose the issue) indicated they have swapped out the thermocouple and wire and the problem stayed with the cylinder. Also indicated that there was no problem for the first several hundred hours, it developed over time. Had he not sold it he was planning to swap cylinders. He also mentioned that it had an "oversized oil cooler" and wondered if that could be an issue but it has been on the whole time, including back when there was no problem.

Before I pull and switch a couple cylinders, any suggestions?

Thanks!

Kevin
N7521K

I'd think an oversized oil cooler would only help matters.

What causes a hot cylinder? Intake air leak at the tube/cylinder interface causing an over lean condition? Some voodoo air flow condition caused by poorly sealed baffling?

Zzz wrote:What causes a hot cylinder? Intake air leak at the tube/cylinder interface causing an over lean condition? Some voodoo air flow condition caused by poorly sealed baffling?

Both of these are what I'd check first. Neither take long to do, intake boot clamps will loosen with heat cycles and require a periodic snug-up (though it also usually manifests as rough running at low power flight like descents). Baffles ma be obvious, or might require you to look closely with the cowl on to see if it's pulling away. Also there should be some little metal air dams between the bottom of the cylinders to force air through the fins, make sure that's there and hasn't wiggled loose.

Do you have a multi point EGT? How does #5 compare to the others? If no multi point EGT, read the plugs, maybe it's running lean. Also check the cooling fins aren't clogged with debris and reducing the airflow over the cylinder at the baffle.

colopilot wrote: Also there should be some little metal air dams between the bottom of the cylinders to force air through the fins

Intercylinder baffles. On Lycomings they tend to be pretty low-maintenance (can't picture the Continental ones), but they can get worn or if one of the hook eyes lets go, it's going to cause problems for both cylinders that it bridges, I'd think.

Zzz wrote:

colopilot wrote: Also there should be some little metal air dams between the bottom of the cylinders to force air through the fins

Intercylinder baffles. On Lycomings they tend to be pretty low-maintenance (can't picture the Continental ones), but they can get worn or if one of the hook eyes lets go, it's going to cause problems for both cylinders that it bridges, I'd think.

One would think, though I could see one side dropping lower or wearing down more depending on how it were secured, especially over hundreds of hours. Actually as I think about it, mine are getting some nice groves worn into them from the cylinder fins. Probably should contemplate replacing them at some point...

Not sure if the baffle setup on your O-520 is the same as the baffle setup on an IO-520, but #5 has long been known as the hot cylinder on IO-520s. There was even a special baffle mod that looked like a scoop to direct more air to #5, but it apparently was killed when the FAA found out it wasn't an STC'd mod. That was a decade or more ago. There was a lot of talk about this on the old Cessna Pilots Association web site. Other than running richer (or lean of peak), the best you can do is fix all of your baffles, seal the gaps with RTV and keep the airspeed up. I also fly ROP with cowl flaps half to full open during summer months. If I can't keep CHTs under 380, I go lean of peak.

FWIW.

Thanks all for the suggestions!

I'll work through those, easiest to hardest, and let you know my results. Will be a bit of time though as I'm on straight floats for another while and "water's edge" A&Ps aren't too common around here.

I do have multi point JPI and the other cylinders run cooler, 360-380 +-.

I'm running ROP and full open cowl flaps for now.

Airflow / airspeed does seem to have some effect as the problem still exists, though not as bad, on wheels.

Kevin

Can't add much than join the club. I have a 185 with a IO-520 and #5 is the hottest also.

Can you / how do you keep it under 400?

The best get-out-of-jail solution I've found on really hot days is running LOP in cruise. Don't know if you can do that, but run the GAMI lean test using your JPI. If the fuel flow spread is small enough and the engine runs smoothly on the lean side, you can run LOP. I lose about 10 knots, but fuel consumption is nearly 1/3 less, and CHTs including #5 are way south of 380--much cooler.

Climb is harder to manage, but it's shorter term. I don't run LOP ever in the climb, so the options/variables available to manage temps are higher fuel flow, lower power settings, lower deck angle, and step climbing once clear of obstacles. I'll do any and all of the above. You might also check to see if your cowl flaps can be rigged to open more at the full open setting than where they're currently set.

-0-

I wouldn’t try running lean of peak with the O-520, fuel distribution just isn’t very even with the big bore carbureted Contis’. You can even things out a bit at some power settings with carb heat, effectively enriching the mixture. Don’t discount the cooling power of fuel.

While still looking for the solution to your #5, here’s an idea to lower all the CHT’s:

The cowl flap cable ends have more adjustment capability than you might realize. We fiddled around with this after installing a cargo pod. Now at the maximum extension, they protrude from the cowling bottom by about an in inch when fully closed. It helped the CHT’s.

On a more difficult level, the cowl louver mod was also effective.

Actually, it sounds like ALL your CHTs are somewhat high. That can happen on floats. Some float installations require cowl flap “extensions”. These are just dxtensions of the actuators that open the cowl flaps further and don’t permit them to close completely.

St the very least, I’d take the suggestion above and adjust the cowl flap actuators to their max open.

MTV

mtv wrote:Actually, it sounds like ALL your CHTs are somewhat high. That can happen on floats.

I'm struggling with what might be obvious...why do engines run hot on floats? Slower cruise speed? Engine working harder to overcome greater drag?

Zzz wrote:

mtv wrote:Actually, it sounds like ALL your CHTs are somewhat high. That can happen on floats.

I'm struggling with what might be obvious...why do engines run hot on floats? Slower cruise speed? Engine working harder to overcome greater drag?

Yes to the above, and also, the drag of the floats can significantly affect the angle of attack of the fuselage in cruise, as in more nose up, which, depending on the cowling, etc, can negatively effect cooling.

But, just going slower with same power or more is a big part.

MTV

http://aerocet.com/wp-content/uploads/2 ... jHSsvix17I

Take a look at page 12 of the first document for this aerocet belly pod install. They add a spacer (Cessna 10-20015) on the end of the cowl flap cable that adds about 1" to the linkage. This lets the flaps open farther. They will still be 1" open when fully closed.

I've heard it can lower CHT by 30-40 degrees. I've also heard of owner produced parts in this case, rather than the $100 cessna part...

What about lower cowl louvers? The Skywagon Club apparently owns the STC now, but I’ve heard it’s hard to find.

I’d be interested in those myself. . . .

StuBob wrote:What about lower cowl louvers? The Skywagon Club apparently owns the STC now, but I’ve heard it’s hard to find.

I’d be interested in those myself. . . .

I'll definitely look into adjusting / extending the cowl flaps. I do have the "shark gill" cowl louvers already.


Kevin



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