High CHT #3, O-360

[DesertNomad]

I am looking for ideas to figure out why #3 is running significantly hotter than the others on a Cherokee with O-360. In cruise it will sit around 370-380, but during climb is difficult to keep under 430. Outside temperature at 5,000' (field elevation) is 70F.

Vy is 74 and a climb at 85-90 will help keep it under 420F, but that still seems quite warm. At Vy to 8000', it will briefly hit 440F.

- The baffling is good - no light escapes behind the baffle wall.
- We are unable to detect any evidence of an induction leak and the intake tube is solid.
- We have swapped CHT temperature probes.
- Compressions are constantly 76-77.
- Oil analysis is normal.
- Oil consumption is normal.
- Engine has about 1650 hours and flies 50 hours a month.
- It starts, flys and runs smoothly.
- The underside of the cylinder has a pink stain that I am unable to find any discussion of, but it is almost certainly from heat. The other cylinders have pink staining too but not nearly as extensive.

Any ideas as to what else I can look at?

 

[Roland Donnell]

Same identical temps issue on my PA28-180 but no pink staining. Maybe iron oxide from a rusty upper plug shell after flying in the rain or iron oxide from a leaking exhaust gasket.


Never gave much value to the missing air filter housing to lower cowl seal until I read this thread. Replacing lowered my hot cylinder temp by 20*C based on an analog gauge.

Piper PA 28 Airbox Intake Seal

This thread https://www.pilotsofamerica.com/community/threads/engine-air-intake.142634/#post-3394261 about a Cessna Airbox seal got me thinking about mine on my PA 28. @Magman mentioned cooling issues if the seal is not tight. My simplistic assumption was any opening in the lower cowl helps...

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[mondtster]

The “pink stain” is discoloration of the paint due to heat.

The #3 cylinder is the leanest/hottest cylinder on an o-360.

 

[DesertNomad]

The “pink stain” is discoloration of the paint due to heat.

The #3 cylinder is the leanest/hottest cylinder on an o-360.

What CHT should I expect to see in a typical climb say from 5,000' to 9,000' on a 70F day? I find it basically impossible to stay under 415F even if I try climbing at 90kts.

 

[Alien Mind]

PA28 - O360, my number 3 hovers just a hair over 400 on climb out of high DA - but only 380 when I occasionally make it across to 'normal' temp/elevations.Back down to 380 ish in cruise at 10,000 DA

 

[Mongoose Aviator]

The temps sounds similar to mine. I watch the CHT #3 and decrease the rate of climb based on the #3 CHT temp.
OP has starting elevation higher than me. OP is starting at 5000’ while I am starting at 500’. Otherwise sounds quite similar.
Once passing ~ 2500’ AGL, I often end up climbing to cruise altitude @ 90~95 KTS IAS so as to keep #3 ~ 400~405.

Cruise @ altitude @ 110 KTS IAS seems to keep #3 happy and below 400. For me.

 

[Hang 4]

Similar to my temps. I'm maybe 10 degrees cooler in climb, but that is done by keeping speed up. I added the airbox intake seal to mine recently, only one flight. OAT was really high at 98 so not sure I saw the effect of the seal. The old one was basically gone. The seal helps prevent the intake scoop from acting like a ram air source that works against the downflow from the main cooling air intake behind the prop. In theory it redirects all the air into the engine intake. I'll see how it does in a more normal temp. I did replace my baffle seals about a year ago and that helped some. The old ones also did not let light through, but I think they were not sealing tight either.

 

[mondtster]

What CHT should I expect to see in a typical climb say from 5,000' to 9,000' on a 70F day? I find it basically impossible to stay under 415F even if I try climbing at 90kts.

Couldn’t tell you, I’ve never flown a Cherokee with an engine monitor.

 

[Domenick]

Are the inter-cylinder baffles installed? In the photo you can see the bracket between cylinders holding the inter-cylinder baffles tight to the cylinder fins.


Is the spark plug cable baffle pass through behind cylinder 3 stuffed with rockwool or sealed in some way? You can see the pass through in the photo below. This one has a tight grommet. The plug leads are not yet attached to the plugs.

 

[Dan Thomas]

The “pink stain” is discoloration of the paint due to heat.

The #3 cylinder is the leanest/hottest cylinder on an o-360.

That there. But the heat is often coming from a leaking exhaust gasket, and that could be squirting a bit of hot exhaust at the CHT sensor, giving a falsely high reading. I have seen it before.

If it is leaking, the exhaust will erode the face of the exhaust port, and if that gets bad enough, the cylinder becomes junk. No gasket can ever seal that up. There's only so much machining room that can save it.

 

[DesertNomad]

Are the inter-cylinder baffles installed? In the photo you can see the bracket between cylinders holding the inter-cylinder baffles tight to the cylinder fins.
View attachment 120084

Is the spark plug cable baffle pass through behind cylinder 3 stuffed with rockwool or sealed in some way? You can see the pass through in the photo below. This one has a tight grommet. The plug leads are not yet attached to the plugs.
View attachment 120086

Yes, and yes.

 

[Stewartb]

Verify your baffle has stand-offs behind #3 to allow air flow. The fin casting is closed on the back of #3 like you can see on the front of #2. It needs space to let air pass.

I’ve blocked most of #1 to improve cooling at #3. #1 barely changed.

 

[RyanB]

That there. But the heat is often coming from a leaking exhaust gasket, and that could be squirting a bit of hot exhaust at the CHT sensor, giving a falsely high reading. I have seen it before.

If it is leaking, the exhaust will erode the face of the exhaust port, and if that gets bad enough, the cylinder becomes junk. No gasket can ever seal that up. There's only so much machining room that can save it.

Ditto. Happened to the Archer and found at annual a year or two ago. Luckily, it was easily honed with the right tool and was saved, but another good reason to check those gaskets frequently to catch it before it gets to that point.

 

[DesertNomad]

Verify your baffle has stand-offs behind #3 to allow air flow. The fin casting is closed on the back of #3 like you can see on the front of #2. It needs space to let air pass.

I’ve blocked most of #1 to improve cooling at #3. #1 barely changed.

Do you have a picture of these stand-offs?

How did you get the sign-off on the blocking plate in front of #1, and do you have specs on it?

 

[Eric Brunelle]

Same here - high #3. 400-420 during climb until I get to cruise climb, then under 400. O360 Archer

 

[Eric Brunelle]

… like this since new (factory rebuild, 350 hours now). Installed all new baffles when replacing engine. Insight G-4 monitor. Runs great, low oil consumption, low oil temperatures. Wish it were lower, but no luck figuring it out. Looks like a common issue with Cherokees and O360’s

 

[murphey]

Same identical temps issue on my PA28-180 but no pink staining. Maybe iron oxide from a rusty upper plug shell after flying in the rain or iron oxide from a leaking exhaust gasket.
View attachment 120081

Never gave much value to the missing air filter housing to lower cowl seal until I read this thread. Replacing lowered my hot cylinder temp by 20*C based on an analog gauge.

Piper PA 28 Airbox Intake Seal

This thread https://www.pilotsofamerica.com/community/threads/engine-air-intake.142634/#post-3394261 about a Cessna Airbox seal got me thinking about mine on my PA 28. @Magman mentioned cooling issues if the seal is not tight. My simplistic assumption was any opening in the lower cowl helps...

www.pilotsofamerica.com

Part source

63086-00 seal air filter Piper Aircraft NEW

NEW Piper Aircraft Parts Online!

www.airpartswest.com

Just checked the air filter housing - I think it's the original and definitely beat up. Guess I'll remove the bottom cowl tomorrow and see what's going on with it,

 

[Stewartb]

No good detail pics but here’s what I have. The installation of cylinders on a Lycoming place deep fins on the front of 1 and 3 and very shallow fins on 2 and 4, thus the shallow face is at the back of 1 and 3. This requires holding the rear baffle off of #3 to allow air to circulate. This is also why #1 is often cooler than the others. My blocking ramp equalizes 1 and 3, and now all 4 have very similar CHTs.

Pic 1 is the back side of #3 as my engine was uncrated. You can see how a close baffle would cause a problem. Pic 2 shows how my baffle is “boxed” to hold it off the back of #3.

 

[Stewartb]

No approval or specs on my front baffle. It took a few tries to find how much of the head to cover and even now I’ve got some aluminum tape added. I’ve done the same to #6 on my Cessna's Continental, also to level the CHTs.