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#6 cylinder CHT’s in climb out

rvanstory

Well Known Member
I have 175 hours on the IO-540 now and MOSTLY have it dialed in where I want.

Most recent change was more restrictor changes to fuel nozzles to get GAMI spread to .2.

All cylinders run GREAT in cruise (350-375 degrees) and all cylinders are under 400 on climb out EXCEPT #6. It goes up to 411. I realize this is fully acceptable, but my anal retentive nature wants to “tweak it” more.

Here’s my question: Who has added a small air dam behind #6 to direct some air down the back fins? It would cover a SMALL portion of oil cooler hole with a bend in it to redirect air. Has this worked for anyone else?
 
following

I haven't done it yet but it is the plan. My thought was not necessary block the oil cooler inlet as much as add a small vane to direct some of the air over that cylinder.

I have the TCW oil cooler valve, and I can actually control the #6 CHT by opening or closing the oil cooler valve. The obvious trade off is if I close that valve down a bit, the CHT decreases but the oil temp increases. Oil temp is usually right around 190, if I close the valve a bit, it gets to about 210-215. Still fine but I understand where you are coming from!:D
 
I have the same problem. In building the baffles I had read posts about #5 running hot for some. And they added a small gap to increase air flow. I reshaped the baffle on the back of #5 and it runs cool. My #1&2 run hotter than #3&4 in climb. I am thinking of cutting down the dams in front of them. But I worry about shock cooling. I did a walk around survey of all the 10's at Oshkosh this year and many had the dams completely removed. I have 75 hours on my 10 now and am still fine tuning things.
Tom
 
Randy, how large is the dam on #2? Initially I cut down the front dams, but ended up replacing them back and around 2/3's the original size. It helped with the rear cylinders slightly. When you climb out do you use full power? I usually pull back to 25" and 25-2600 at 125kts in the climb, especially on hot days.
 
My experience

I had a similar experience with my 10 but when I realized that the cylinder that broke 400 in climb out also peaked first, I then changed out it’s restrictor so that it peaked last. I still got a similar gami spread, but that cylinder now does not go over 400 in climb out.
 
Randy, how large is the dam on #2? Initially I cut down the front dams, but ended up replacing them back and around 2/3's the original size. It helped with the rear cylinders slightly. When you climb out do you use full power? I usually pull back to 25" and 25-2600 at 125kts in the climb, especially on hot days.


#2 dam was cut mostly off. Might try adding one back. I climb out full throttle but 2500 rpm. Lower MP hasn’t seemed to change things much.
 
I have the same experience. #3 & #4 are a good 40* cooler, so I am considering some type of diverter that will push some of the air flow back to #5 & #6. Haven't gotten around to it yet though. I have the stock cooler, so already get to 215 or 220* in climb and closing off flow to it isn't an option.

Larry
 
I struggled with CHT issues the first 30 or so hours. I did all the usual things people suggest; washer trick, glassed in the governor cut out, build a dam around my alternator belt, put RTV all over the place. It got them to a place where even a hot day I could keep most everything under 400 and shallow out to 115 knots and only #6 would push 410 or so. In cruise everything is sub 360 and I would lean to keep #6 under 370.

260 hours in I decided this oil change I would redo a number of things to see if I could do better and did the following;

- First I removed the dams from #1/2.
- I replaced the baffles with the McFarlane stuff and on some of the more complex cuts in the front I used some black Silicon stuff.
- I also secure it using strips of aluminum with nutplates to hold it tight, RTV'ing the baffling material and walls. Some spots mainly in the front where strips didn't make sense I used these little screw baffle gromets.
- I hammered out a duct for #5 instead of using the 'washer trick'
- I made a small dam/ramp behind #6 covering maybe 10% of the oil cooler inlet to direct air down behind the cylinder.
- Finally reapplied RTV to any spaces and behind the baffling material.

Took her up this afternoon (93 degrees) and am extremely happy with the results. I took off and climbed at 90 knots (Vy) all the way to 10,500 and no CHT got over 400. After flying around and heat soaking my engine a bit I did a touch and go and again climbed out at Vy with no CHT going over 400. Comparing that to a flight a few weeks ago when it was 96 out, I climbed with #6 peaking to 408 having to maintain 115 knots, I would say my cooling has improved substantially.

In cruise everything is about the same as it was, I could lean it an extra .2 GPH so no real gains with that.

#6 is still the hottest cylinder so my next test is to bend my air dam up a bit more to hopefully promote more air directed down behind it. Also not adverse issues with my oil temp.



 
- I made a small dam/ramp behind #6 covering maybe 10% of the oil cooler inlet to direct air down behind the cylinder.

Thank you Justin for sharing this! I made an air dam exactly like yours for #6. Still finishing up annual, but should do test flight later this week. I'll report back.
 
Justin, do you have a picture of what you did behind #5? Thanks, Lynn

I struggled with CHT issues the first 30 or so hours. I did all the usual things people suggest; washer trick, glassed in the governor cut out, build a dam around my alternator belt, put RTV all over the place. It got them to a place where even a hot day I could keep most everything under 400 and shallow out to 115 knots and only #6 would push 410 or so. In cruise everything is sub 360 and I would lean to keep #6 under 370.

260 hours in I decided this oil change I would redo a number of things to see if I could do better and did the following;

- First I removed the dams from #1/2.
- I replaced the baffles with the McFarlane stuff and on some of the more complex cuts in the front I used some black Silicon stuff.
- I also secure it using strips of aluminum with nutplates to hold it tight, RTV'ing the baffling material and walls. Some spots mainly in the front where strips didn't make sense I used these little screw baffle gromets.
- I hammered out a duct for #5 instead of using the 'washer trick'
- I made a small dam/ramp behind #6 covering maybe 10% of the oil cooler inlet to direct air down behind the cylinder.
- Finally reapplied RTV to any spaces and behind the baffling material.

Took her up this afternoon (93 degrees) and am extremely happy with the results. I took off and climbed at 90 knots (Vy) all the way to 10,500 and no CHT got over 400. After flying around and heat soaking my engine a bit I did a touch and go and again climbed out at Vy with no CHT going over 400. Comparing that to a flight a few weeks ago when it was 96 out, I climbed with #6 peaking to 408 having to maintain 115 knots, I would say my cooling has improved substantially.

In cruise everything is about the same as it was, I could lean it an extra .2 GPH so no real gains with that.

#6 is still the hottest cylinder so my next test is to bend my air dam up a bit more to hopefully promote more air directed down behind it. Also not adverse issues with my oil temp.



 
.... Who has added a small air dam behind #6 to direct some air down the back fins? It would cover a SMALL portion of oil cooler hole with a bend in it to redirect air. Has this worked for anyone else?

Just curious if you made this dam modification to direct airflow behind the #6 cylinder? I am having the same problem with CHT's running consistently around 405 in level cruise on the #6.
 
Just curious if you made this dam modification to direct airflow behind the #6 cylinder? I am having the same problem with CHT's running consistently around 405 in level cruise on the #6.

I did. Still working a little on it. I started with a 1.5" plate. Not near large enough. Now have about 4" one. Seems to have lowered my climb out temps by about 10 degrees without affecting oil temps. My cruise temp on #6 is good. It's only in climb I was looking for lower.

I was waiting for final tweaks before I posted pics. What made the biggest difference for my cruise temps was Dan Horton's flashlight trick. Turn out lights in hangar, close hangar door, then shine bright flashlight from under engine. Where you see light, you have leaks. RTV those gaps made a big difference for me.
 
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