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High cylinder head temps

flybikedave

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I recently purchased a RV9A and am experiencing high CHT (475+). Single probe on #4, behind which is oil cooler. Would greatly appreciate advice comments. Will cowl flaps be needed?
 
Start with the baffles, they cannot waste any cooling air. Buy some high temp RTV and put a light in the lower cowl under the motor. Any light you see other than the cylinder fins needs to be goobered. Check the mag timing, too advanced makes it hot. I hope you are climbing at full throttle, even a small throttle reduction makes the CHT?s on my non-injected -10 go up dramatically, (assuming its auto-rich function of the carb)
 
search

Welcome to Van's AF. The search engine is your friend. Trust me.
High CHT's have been experienced and solved by many here. If you search the topic and begin your research, you will be able to approach your solution with data and builder tips in hand.
I own a 9A and even now.... do a step climb on warmer days. With temps as high as you mention... I would do a step climb right away, to mitigate damage to cylinder heads. Just pull the power back a bit and lower the nose. You will see temps drop quickly. Then you can ease the power back in and pitch up.
You will be well served with instrumentation that gives you visibility to ALL cylinders and EGT's. Products are cheaper and better than in the Cessna single probe days. Solutions are not that costly, and certainly less than top overhaul.
Antisplat makes a nice operating cowl flap that may be an option. Simple modifications to baffles are all some owners have needed.
So, begin to look around at previous posts and take notes.
Again, welcome.... and enjoy!
 
Find a local builder and ask them to come take a look. To get CHT's that high, either the baffles are totally messed up, the timing is wY off, there is an induction problem, and/or a mixture issue.

Either way, don't fly it again until you figure this out.
 
Do what you can with the cowl off.

475 is so grossly high the first thing to look at is to confirm the inst. indication is valid.

Easy to test, and timing is too. Both while the cowl is off. Others will require flight testing.
 
What phase of flight are you experiencing this temperature at?

If you try to climb out at Vy you are likely to experience elevated temperatures. It seems to be a popular choice to climb out at ~110 knts,
 
I recently purchased a RV9A and am experiencing high CHT (475+). Single probe on #4, behind which is oil cooler. Would greatly appreciate advice comments. Will cowl flaps be needed?

I had a similar problem with CHT that would spike very high on #2. Stay there for a while and then go down. Replaced Dynon CHT probe/sensor, and problem went away. Simple check would be to swap sensors 2 and 4 and see if issue follows sensor.

Even on the hottest days I don't see CGTs above 350. and they are all within about 20 degrees. I do not have any RVT sealing my baffles. I just have the close seal created by baffles that fit well.
 
The search engine is indeed your friend! I had uneven, and 2 cylinders high..used to do the step climb routine..but searched out info here and made mods..now my CHTS are all within 15 to 20 degrees all the time..even in full power climb. All the mods I did were to the baffles. I had the stock VAns baffleing and its not very good. What made the most difference was creating the "bypass" areas on the left rear and right front cylinders, where the fins are almost nonexsistant. I also looked at a piper on the field, and a Grumman yankee, both with O-320's and saw that they both have these types of "tunnels" to get the airflow around to the bottom of the cylinder. its been awhile, but there are good descriptions and pics right here on the forums. ALso you should get CHT monitoring on all 4 if you dont have it...that way you can see your progress better.
 
I recently was asked to market an RV-6-A for a friend. When I flew the aircraft to my hanger to detail and test all functions, the cylinder head temps peaked at 425 degrees on climb-out. I decided this would be problem, I must address before sale to an unsuspecting buyer. I got to work cutting the front baffle ramp so I could remove the white latex caulk that the owner had mistakenly applied thinking it would, in his words "force more air into the cylinder cooling fins". I cut way the ramp left and right and created a smooth bend into the entry point of the cooling fins. ON the first test, I knew I had solved the problem! The cylinder heads peaked at 375 degrees on a full throttle climb-out at 90 knots on a 92 degree day.

The latex caulk turned out to be only part of the problem. The Vans designed baffling is much to tight agains the smooth forward face of the Lycoming cylinders restricting cooling air to cylinder #1 and #2 cylinders. As can see on the photo, the entry of cooling air is much enhanced to the open gap between the cooling fins and the air now follows a nice curve down into the bottom fin area. I encourage anyone building an RV with a Lycoming engine to leave about a 1/2 inch of open space between the into of the baffle ramp and the forward cylinder or even better create a smooth curved, as I did at the cylinder/baffle interface...............Carl
 

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I encourage anyone building an RV with a Lycoming engine to leave about a 1/2 inch of open space between the into of the baffle ramp and the forward cylinder or even better create a smooth curved, as I did at the cylinder/baffle interface...............Carl
Unfortunately, this advice is contrary to the mechanics of the downdraft cooling system seen on most Lycomings. Entry air flows from the top, and the baffling makes sure that the airflow stays in contact around the circumference of the cylinder and head picking up heat, finally discharging at the bottom. Proper baffling is particularly important in an air cooled engine to ensure equal cooling around the entire cylinder. I believe the scheme you have come up with throws a LOT of air at the lower fins, yes, but at the expense of the top. Yes, there is indeed a shallow spot on the head at the front of #2 and the back of #3 which blocks airflow, but that has been discussed and solved ad nauseum on this forum. It’s unlikely your modification will result in damage, but before people blindly take your advice it’s important to point out the downsides of possible asymmetric cooling.
 
I recently purchased a RV9A and am experiencing high CHT (475+). Single probe on #4, behind which is oil cooler. Would greatly appreciate advice comments. Will cowl flaps be needed?
Like others have said 475 is dangerously high, easy things to check in preferred order...

1. Probe calibration...check in boiling distilled water and measure adjusted for elevation/pressure. Your'e not looking for accuracy to land on the moon, but probe should be close. I checked mine after my engine overhaul and they were all within 1 degree of expected boiling point.
2. Timing...make sure the aircraft is timed correctly
3. Baffling...cowl aircraft and look for any gaps...front or back. Top cowling will also show you where "dirty" air is escaping as it leaves little witness marks
4. Exit restrictions...cowling exhaust is more important than intake
5. Fuel flow...make sure it's rich enough, only after the above have been checked

I have a RV-9A and climb out at 100 KIAS indicated and even on hot days I rarely see 400F. Living in WI my biggest issue is keep temps up when flying lean of peak in the winter.
 
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I recently was asked to market an RV-6-A for a friend. When I flew the aircraft to my hanger to detail and test all functions, the cylinder head temps peaked at 425 degrees on climb-out. I decided this would be problem, I must address before sale to an unsuspecting buyer. I got to work cutting the front baffle ramp so I could remove the white latex caulk that the owner had mistakenly applied thinking it would, in his words "force more air into the cylinder cooling fins". I cut way the ramp left and right and created a smooth bend into the entry point of the cooling fins. ON the first test, I knew I had solved the problem! The cylinder heads peaked at 375 degrees on a full throttle climb-out at 90 knots on a 92 degree day.

The latex caulk turned out to be only part of the problem. The Vans designed baffling is much to tight agains the smooth forward face of the Lycoming cylinders restricting cooling air to cylinder #1 and #2 cylinders. As can see on the photo, the entry of cooling air is much enhanced to the open gap between the cooling fins and the air now follows a nice curve down into the bottom fin area. I encourage anyone building an RV with a Lycoming engine to leave about a 1/2 inch of open space between the into of the baffle ramp and the forward cylinder or even better create a smooth curved, as I did at the cylinder/baffle interface...............Carl
A lot of RVs actually have a dam on #1 and #2 to force more air to back jugs. The RV-9A kit comes with these dams...

https://store.vansaircraft.com/cb-1000b-cowl-baffle-air-dams-left-and-right-cb-1000b.html
 
You did not state the engine, but I assume it is a o320. I have higher-than-I-like CHTs too. But mine are OK as is. My problem comes from the right side cowl ramp that is attached to the upper cowl. The O320 is pretty far forward in the 9A, and this causes the gap between the front cylinder (#1) and the top cowl ramp to be very close. The cowl ramp on the top cowl needs to be fiber glassed in as far forward as possible. One should be able to put a hand between the gap. I had barely 1" gap during my phase one; thankfully I wasn't making much power. after Phase 1 and engine break in, I moved the center of the ramp forward bout an inch. This allowed me to keep the same baffles but really improved the CHTs on the right side. Here is a before and after picture.
 

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