Hi everyone,

I’m still learning this engine and haven’t flown as much as I’d like so far this year, so I’m uncertain when this started but I’m seeing a higher CHT on cylinder 5 (front most pax side) that is hot enough to dictate how I run the engine. The rest of the cylinders are plus or minus 10 degrees, a great spread IMO, but #5 is about 50 degrees hotter than the coolest cylinder. While ROP, I’m burning 25% more fuel than POH numbers to keep it below 380 while the others are chilling at 330-340. EGT spread is very low across all cylinders.

My mechanic replaced the baffle seals earlier this year, so I’m going to do some flashlight testing and see if there is any room for improvement.

Any other ideas?

Also, I’ve attached a photo of a non-OE baffle in front of cylinder 5 that looks suspicious to me. I have no idea why it’s there. Does anyone recognize this?

Take that thing off and see what happens. I had same thing on mine and took it off.I guessed it was for cold weather ops or something. Brought that cylinders temp down a touch . I figure the more air hitting the cooling fins the better .

I have the exact same issue on my naturally aspirated I/O 550. I have the larger oil cooler and I think that contributes to the higher temperatures in number five the stock baffles on mine rise up a few inches above the oil cooler, but have a tab that goes higher in the same position as the tab you have. I have wondered about removing the whole piece of baffle in front of the cylinders, has anyone done this? Or cut them down?

The oil cooler is a good point, I feel like I stumbled across a remote mount oil cooler, I’m unsure if it was supplemental or a replacement. Are you guys familiar with anything like that?

I was about to type "welcome to IO520 land," but I guess 550s can have the same issue. I've struggled with this on my normally aspirated IO520F for 20 years. Mine also has the large oil cooler. Oddly, #6 is my coolest cylinder, by 80 degrees. I've replaced all of the baffles, gooped the heck out of the joints with RTV, and flown both with and without the stock baffle that rises up over the cooling fins of #5. The only big difference I noticed was when I switched to GAMI-jectors a few years ago--and it got worse!

I figure that Continental probably put more fuel through the #5 injector on account of the temperature problem. In compensation, though, I can run lean of peak without difficulty. I still climb ROP, and have to pour obscene amounts of fuel through in order to keep #5 below 410 (yes--410 df) on warm days, but, once I get up to altitude, I can go LOP and all the CHTs come down nicely. Number 5 remains the hottest, so I adjust cowl flaps to keep it at or below 380 df. I lose a little bit of speed, but have been getting over 10 mpg on my usual 45 minute flight with 6,000' climb. It does even better up higher and on longer legs. Not that I got the 206 to save money . . .

Years ago, someone who frequented the Cessna Pilots Association came up with a custom baffle for #5 that reportedly licked the problem. I even had a picture of it for a long time. As I recall it looked like a scoop with the opening facing forward right above the oil cooler and channeled the air down and into the cooling fins of #5. Another CPA forum participant apparently objected because they didn't have an STC for it. The fix disappeared right about the time I got the 206, so I (and everyone else since then) was SOL. If anyone out there remembers this fix, or, even better, has a picture, I'd sure like to see it, just for auld lang syne, of course.

CAVU

I’d also really like to see that modification.

I’m still dumping a lot of fuel into this thing, but removing that little baffle appears to have knocked 10* off of #5. I’ll have to fly a few more times to confirm a step change.

Well there ya go .

I have a low res scanned copy of what I believe to be the original scoop design. I'm going to have one of my guys recreate it in CAD sometime in the next week or so.

I'm wondering how difficult it would be to STC this thing?