#3 CHT Running Hot

[THEAirplanegirl]

Alright... I have a long winded question for the much more experienced and knowledgeable super cub pilots... Do you guys have any more ideas to help with CHT cooling? I know that is a broad open ended question but here is the back story:

I recently did a top overhaul on my O-320-A2B narrow deck. This is a low time motor. Complete overhaul in 2010 after sudden stoppage (previous owner). All parts were sent out to the appropriate places. New cam and crank at that time. The plane got about 100 hours on it before it sat for about 7 years until I purchased it. If you have seen any previous posts then you know we have done a lot of work to it. We ended up topping it for a series of reasons and ultimately found 3/4 cylinders to have cracks. They were new OH cylinders... Not sure why they had cracks after only 100 hours but that is a question for another day.

Prior to top end I did install a full Dynon EMS and realized my #3 was running exceptionally hotter and leaner than the rest. 420+ CHTs and 1500+ EGT on take off and always 40-50 degrees hotter than the rest. This problem was never officially found as we decided to pull all the cylinders and do a multitude of other things. So far we have removed mags and had those overhauled. New ignition harness. Timing has all been checked. Do not think it's a timing problem.

Fast forward to now... 4 new superior cylinders with 8.5:1 compression. I am experimental and after much discussion with other cub drivers, mechanics, and even Lycon, I decided to go with the higher compression pistons on the narrow deck. Cylinders were also sent out to Lycon to be port and polished. At this time we also replaced/checked everything to do with the intake tubes. Installed SDS Aero O-ring sealed induction tube flanges. These use a Viton O-ring instead of a paper gasket. Cam looked great even after sitting for 7 years (that was always a worry). I also previously had a -32 carburetor. Ultimately decided to install a new 10-5217 carburetor as I was told it atomizes better in anticipation of higher CHT temps with the higher compressions. Installed new dual crossover exhaust from Custom Aircraft Parts... kind of like if a Vetterman and Sutton exhaust had a baby.

Break in went great. Burned less than a half qt of oil in the first 10 hours. CHTs during break in ran about 385-410 while running it between 2450-2550. Kept it a little richer for the break in. Dropped mineral oil at 10 hrs. Mind you this is all happening in the winter in Michigan so it's very cold out right now. The first flight after break in, it was 18 F out. At 2350 leaned out to 6.5 gal/hr, the numbers were CHTs 358-382. EGT’s 1380-1420. However, we recently had a 50 degree day and of course I took my plane out to fly it! Well even at that temp I had a hard time keeping my CHTs below 400, especially the #3 again.... I had to keep it a lot more rich than I ultimately would like. I am just worried once summer comes I am going to have even more of an issue. Maybe I am being too picky/fussy. But I would like to at the most be able to keep them below 400 ideally 380, but I am not sure 380 is possible with my current set-up. I should add that I have a standard piper cowling, front mounted oil cooler, and my oil temps have been running 170-180 on the cold days.

Am I missing something? I do find it odd that the baffling for the super cubs is not up against the back of the cylinder on #3 & 4. That extra space seems like it would not be conducive to cooling. I've debated if it's worth my time to try to change that? When we put the baffling back on after the top end we made sure to close any unwanted openings. Added some ramps to the front baffling to help direct airflow.

I would also like to hear how you operate/manage your engines. I am always open to constructive criticism and learning. In the end, I just want to be safe and have engine longevity. I know this is always a big debate but I personally have always cared more about CHTs than EGTs. I look and pay attention to my EGTs for many reasons, but care more about my CHTs for cruise/leaning. In the ideal situation, where temps weren't an issue, I usually lean until the engine runs rough and then enrich just until it smoothes out.. or in other words I try to stay either lean of peak or no more than 20 degrees rich of peak. I also only enrich with descents when the engine tells me it needs it and never go full rich in the pattern at low RPM. I was taught the "big hand" in the event of a go around... and in my head it seems like having it full rich at lower RPMs in the pattern is about the same as having it full rich on the ground... maybe not...

Anyway, LONG post with multiple questions. I guess I am just trying to figure out if there is something more I can do to help with cooling whether that be with my own engine management or with some alteration. Does #3 typically run hotter than the rest?

 

[DENNY]

Stop leaning so much!!! Remember cold air is a lot more dense. You basically have a 160 hp engine, it will run that lean but you are going to have higher CHT'S. You have a 4 cylinder CHT/EGT so use the information it gives you to adjust the mixture. Do all hard climbs full rich and full throttle that will allow more fuel to help cool the cylinders. At 2400 rpm you should be able to get a 150 degree EGT drop when leaning. This will mean the carb is not running to lean. Depending on exhaust system usually a 150 rpm drop with carb heat. Ramps look great, that space behind # 3 is important temps will be higher if it is flush to cylinder. See how your temps look running 8 GPH at 2400 RPM. I normally run 325 -345 on my CHT'S. Are you running 100LL or mo gas. 100 LL tends to run a little cooler. Every plane/engine/pilot is different so just because some one says they can get 6 mph out of a 0320 you have to ask what altitude ,rpm, plane, prop, to compare to yours. Prop matters a lot, a flat STOL prop runs cooler than a cruise prop.
DENNY

 

[THEAirplanegirl]

Stop leaning so much!!! Remember cold air is a lot more dense. You basically have a 160 hp engine, it will run that lean but you are going to have higher CHT'S. You have a 4 cylinder CHT/EGT so use the information it gives you to adjust the mixture. Do all hard climbs full rich and full throttle that will allow more fuel to help cool the cylinders. At 2400 rpm you should be able to get a 150 degree EGT drop when leaning. This will mean the carb is not running to lean. Depending on exhaust system usually a 150 rpm drop with carb heat. Ramps look great, that space behind # 3 is important temps will be higher if it is flush to cylinder. See how your temps look running 8 GPH at 2400 RPM. I normally run 325 -345 on my CHT'S. Are you running 100LL or mo gas. 100 LL tends to run a little cooler. Every plane/engine/pilot is different so just because some one says they can get 6 mph out of a 0320 you have to ask what altitude ,rpm, plane, prop, to compare to yours. Prop matters a lot, a flat STOL prop runs cooler than a cruise prop.
DENNY

Thanks Denny! I don't think I am necessarily over leaning it. I am definitely leaning based on EGT/CHT temps and I also occasionally verify with my "lean assist" on the Dynon. I don't use it every time as eventually you do just learn your specific plane and what it likes. I am running a Sensenich ground adjustable composite prop. Right not I have it on the #2 pitch... haha which what that equates too I am not exactly sure.. & funny you mention that but next flight I was planning on checking my EGT drop spread with leaning to make sure the carb isn't running too lean! Thats definitely next on my agenda!

 

[Mr. Ed]

I hung a new Lycoming on my plane last year. Lycoming manual recommends 100* ROP EGT for leaning. Personally, I wouldn’t try running LOP until you get your cooling issues rectified and all cylinders running very close to each other.

Looks like exhaust leak residue on #3 spark plug terminal cap & wire? Do you have a lip on the lower cowl opening?

 

[aktango58]

6.5 gallons an hour is NOT enough fuel for an O-320. What you like for lean and what the engine likes are two different numbers, listen to the engine

 

[bcone1381]

You might read the first post on this Van's RV forum and see if this issue of the cylinder casting applies to your baffling. https://vansairforce.net/threads/baffle-mod.37835/

 

[acroeric]

I hung a new Lycoming on my plane last year. Lycoming manual recommends 100* ROP EGT for leaning. Personally, I wouldn’t try running LOP until you get your cooling issues rectified and all cylinders running very close to each other.

Looks like exhaust leak residue on #3 spark plug terminal cap & wire? Do you have a lip on the lower cowl opening?

I noticed the exhaust soot on the #3 cap and wire as well. Also- what is that scat tube going to that runs between the intake/ exhaust tubes and the cylinders? Airflow around those areas is a premium.

Carbs are notorious for having uneven fuel distribution. I personally never try lean of peak with a carb. I really never lean that aggressively with a carb at all.

In my experience #3 is going to be the hottest unless you have an oil cooler behind #4.

Are you running a "Tractor Baffle"?

Post some pictures of your entire cowling installed, of both sides open, the front, and of the cowling exit at the bottom if you have them.

 

[fobjob]

Check the intake tube on your #3, found the rubber hose connector on mine had been cinched down too tight, which caused the intake tube to buckle, the crease extended just beyond the edge of the hose, creating a barely visible air leak….

 

[Supercub Works]

Lots of good suggestions I see. On most carbureted Lycoming 4-cylinder engines #3 is usually the hottest. Some 160HP STC conversions required an added lip to the lower cowl to help increase the low pressure to increase airflow. Looks like you installed new cowl seals, does it all lay flat to the cowl? I'm old school and prefer the felt seal instead of the flat silicone type. I've never been a fan of silicone to seal the small gaps, but I see that allot. I'm sure it can help but I just don't like to see silicone on many places on an airplane. Modern engine analyzers are great, but this is usually what happens when you get all that information. Be sure to calibrate your lean assist carefully. I'm able to get about 7 GPH at 2400 RPM/1450 but 8 is a better number at higher power settings for my 150HP engine with port/polished cylinders and F A Dodge hot rod muffler. Sometimes a break in can take more hours than we expect, temps can still drop. Great to hear your cub is back in the air!

 

[tackdog]

I’m not an IA - A@P, yet owned a few 0-320 - 0-360 carb fed engines and fly in Arizona type weather. I had an Rv7 with massive cylinder 3 overheat issue like you describe and understand that flying a cub at 80 knots versus an RV at 150 are two different animals for some Coolings issues… I had the vans metal baffle where the baffle around the rear of no.3 was touching the cylinder with no gap but through the cooling fins was the only air flowing. With the poor casting marks (as is shown in that web link) in the fins, stuff all air was flowing and the ‘poor man’s rear baffle mod’ was to simply add a few washers under the baffle mount which spaced the baffle out a few mm, and this alone saw a large CHT drop. the other mod a bunch of RV’ers did, was to form this tiny bypass scoop / scallop in the rear of this baffle - the scoop literally only places not even half an inch clearance behind a part of the cylinder) The second thing suggested to me that worked well, was blocking off some air to the front air dam so more is deflected over the top and to the rear. (Rob Peter to give to Paul)…’ To ‘experiment’ I just used some high temp metal flashing tape - that is found at bbq - fire place installation type shops, and laid this across the front cylinder face and adjusted the tape size each flight / and once sorted, made a new alloy deflector. I was suprised how much this worked and for such little investment! (I’d already chased for months, dealing every air leak with rtv sealant). On your baffle, that looks like quite a large space behind no 3 - maybe that’s just flowing too
much air to be efficient?) yet, I’m not experienced in cubs so perhaps that’s needed for the slower cruise speeds too? When I go out to my hangar tomorrow, I’ll take a photo of the no3 deflector scoop I made for my cub following the RV forums so you can see just how small space is needed.. (I’m going with the carbon plenum at the moment, but have an RV7 baffle kit ready to install if needed - as they are soo damn cheap) …. I hope you find the issue … Damian

 

[Steve Pierce]

Have you swapped the #3 probe with another to see that they show the same thing? My #4 is hottest but that is where my oil cooler is.

 

[OLDCROWE]

Assuming all your probes are equal.

I have a wide deck O320 with 8.5:1's that the cylinders had all the fun worked into them plus the carb has been flowed and had some love as well so much that with a CGR 3P monitor I can lean it by the numbers almost like I can in my fuel injected Sky Wagon (but the cub heats up far faster if you lean a bit too much) and the only time I see 6.5 gph in cruise is when I'm WAY up high going from point A to point B or when I'm putting around down low rubbernecking the sights

Always remember Fuel is a cylinder coolant and given the funds you have put into your engine it is the cheapest thing you'll put into the equation. So my thought is to either pull the throttle back or push the red knob in some more and go have some fun.

 

[DENNY]

With a carb the throttle plate in the carb has a large effect on airflow so you will see different temp spreads at different throttle settings. After 2550 the economizer port is exposed allowing more fuel into the carb. This will help with cooling during climb out, so do all but shallow climbs at full throttle vs 2500 or below you should see the difference in the CHT spread. In a hard climb with my cub #2 is the hottest with #3 and #4 CHTs usually drooping some that is a combination of fuel delivery and airflow. The exhaust valve guides take a beating at hight CHTs that is why they have the "wobble test" SB. You could very well have a small air leak effecting # 3. Did you put the primer system back in? if so check the lines and fittings carefully. If you have a manifold pressure gauge check that line also. One of the reasons cylinder crack is excessive CHTs.
DENNY

 

[krines]

Topped my 0-320 B2B with Lycon ported and polished cylinders. Went to break in using the -32 carb and CHTs were 425 and EGTs 1425. Went back to the barn quickly. Got to thinking about it and there is significantly more air flowing through the engine now. Called Lycon and they recommended the carb you have. Put in the new carb and now my CHTs are 385 and CHT about 1380. You have to realize this drastically changes the engine. These engines will now dyno at over 180hp and as such you will burn much more fuel. Prior to this change I used to lean regularly. Now I almost never do. These are fire breathing dragons. No longer 4 hour fuel endurance. Everytime I check spark plugs they look like they have been run very lean. Uneven CHT could be other things. I am just saying you now have a hotter engine.

 

[THEAirplanegirl]

I hung a new Lycoming on my plane last year. Lycoming manual recommends 100* ROP EGT for leaning. Personally, I wouldn’t try running LOP until you get your cooling issues rectified and all cylinders running very close to each other.

Looks like exhaust leak residue on #3 spark plug terminal cap & wire? Do you have a lip on the lower cowl opening?

Thanks! Yes! I have not been running it lean at all. I was more just stating what I would normally do... Break in I ran rich and since Ive been running it to whatever it needs to be the appropriate temps.

I do have a lip... Just the one that comes on a standard PA-18 lower cowling. The residue it from my previous exhaust leak. I had a pretty bad one on my #3 that I had to doctor up pretty good... The old cylinder exhaust flange had pretty bad pitting and so we controlled it the best we could.. knowing it required the cylinder to come off to completely fix it... which ultimately ended up happening.

 

[THEAirplanegirl]

I noticed the exhaust soot on the #3 cap and wire as well. Also- what is that scat tube going to that runs between the intake/ exhaust tubes and the cylinders? Airflow around those areas is a premium.

Carbs are notorious for having uneven fuel distribution. I personally never try lean of peak with a carb. I really never lean that aggressively with a carb at all.

In my experience #3 is going to be the hottest unless you have an oil cooler behind #4.

Are you running a "Tractor Baffle"?

Post some pictures of your entire cowling installed, of both sides open, the front, and of the cowling exit at the bottom if you have them.

I am not exactly sure where the baffling was purchased, but I know it was replaced with new at original overhaul... before I purchased it. The scat tubing is the cabin heat running from my front heat muff to the air box on the fire wall

 

[THEAirplanegirl]

Check the intake tube on your #3, found the rubber hose connector on mine had been cinched down too tight, which caused the intake tube to buckle, the crease extended just beyond the edge of the hose, creating a barely visible air leak….

If I am understanding what youre saying, we did just change out all of the intake components including the nitrile hoses. The kit came with constant tension clamps instead of worm-drive clamps

 

[skywagon8a]

I am not exactly sure where the baffling was purchased, but I know it was replaced with new at original overhaul... before I purchased it. The scat tubing is the cabin heat running from my front heat muff to the air box on the fire wall

That scat could easily be restricting the airflow causing #3 to overheat. Move it to outside the intake tubes.

 

[THEAirplanegirl]

Lots of good suggestions I see. On most carbureted Lycoming 4-cylinder engines #3 is usually the hottest. Some 160HP STC conversions required an added lip to the lower cowl to help increase the low pressure to increase airflow. Looks like you installed new cowl seals, does it all lay flat to the cowl? I'm old school and prefer the felt seal instead of the flat silicone type. I've never been a fan of silicone to seal the small gaps, but I see that allot. I'm sure it can help but I just don't like to see silicone on many places on an airplane. Modern engine analyzers are great, but this is usually what happens when you get all that information. Be sure to calibrate your lean assist carefully. I'm able to get about 7 GPH at 2400 RPM/1450 but 8 is a better number at higher power settings for my 150HP engine with port/polished cylinders and F A Dodge hot rod muffler. Sometimes a break in can take more hours than we expect, temps can still drop. Great to hear your cub is back in the air!

Thank you! I am glad its back up and running! I actually used the soft side of velcro. The original felt was all worn and coming apart. I usually run about 2300/1375-1420 egt. I looked at some of my old pics from this past summer of what I was seeing before top. Ill link it in

 

[THEAirplanegirl]

On your baffle, that looks like quite a large space behind no 3 - maybe that’s just flowing too
much air to be efficient?) yet, I’m not experienced in cubs so perhaps that’s needed for the slower cruise speeds too? When I go out to my hangar tomorrow, I’ll take a photo of the no3 deflector scoop I made for my cub following the RV forums so you can see just how small space is needed.. (I’m going with the carbon plenum at the moment, but have an RV7 baffle kit ready to install if needed - as they are soo damn cheap) …. I hope you find the issue … Damian

That was my thought process too... it seems like too much space to direct airflow but this is what I am seeing on majority of cub cowlings. I've been nosy and trying to look around and at any ones I can find...

 

[THEAirplanegirl]

Have you swapped the #3 probe with another to see that they show the same thing? My #4 is hottest but that is where my oil cooler is.

I have not. I just installed this system and it only has maybe 25 hrs on it. I definitely could try that though. I have a front mounted cooler so I don't seem to have any issue with #4.

 

[THEAirplanegirl]

Assuming all your probes are equal.

I have a wide deck O320 with 8.5:1's that the cylinders had all the fun worked into them plus the carb has been flowed and had some love as well so much that with a CGR 3P monitor I can lean it by the numbers almost like I can in my fuel injected Sky Wagon (but the cub heats up far faster if you lean a bit too much) and the only time I see 6.5 gph in cruise is when I'm WAY up high going from point A to point B or when I'm putting around down low rubbernecking the sights

Always remember Fuel is a cylinder coolant and given the funds you have put into your engine it is the cheapest thing you'll put into the equation. So my thought is to either pull the throttle back or push the red knob in some more and go have some fun.

Thank you! I do try to baby my engines the best I can. I don't usually run them hard and try to be very observant of my temps. However, this seems to be the consensus so I will definitely try to run it more rich. So far, I really haven't been running too lean since top as the temps just have been high.

 

[THEAirplanegirl]

With a carb the throttle plate in the carb has a large effect on airflow so you will see different temp spreads at different throttle settings. After 2550 the economizer port is exposed allowing more fuel into the carb. This will help with cooling during climb out, so do all but shallow climbs at full throttle vs 2500 or below you should see the difference in the CHT spread. In a hard climb with my cub #2 is the hottest with #3 and #4 CHTs usually drooping some that is a combination of fuel delivery and airflow. The exhaust valve guides take a beating at hight CHTs that is why they have the "wobble test" SB. You could very well have a small air leak effecting # 3. Did you put the primer system back in? if so check the lines and fittings carefully. If you have a manifold pressure gauge check that line also. One of the reasons cylinder crack is excessive CHTs.
DENNY

Thanks! I did not put the primer back in and I actually just switch out and checked everything to do with my manifold pressure. Dynon changed over to a different sensor so I had to swap it out!

 

[THEAirplanegirl]

Topped my 0-320 B2B with Lycon ported and polished cylinders. Went to break in using the -32 carb and CHTs were 425 and EGTs 1425. Went back to the barn quickly. Got to thinking about it and there is significantly more air flowing through the engine now. Called Lycon and they recommended the carb you have. Put in the new carb and now my CHTs are 385 and CHT about 1380. You have to realize this drastically changes the engine. These engines will now dyno at over 180hp and as such you will burn much more fuel. Prior to this change I used to lean regularly. Now I almost never do. These are fire breathing dragons. No longer 4 hour fuel endurance. Everytime I check spark plugs they look like they have been run very lean. Uneven CHT could be other things. I am just saying you now have a hotter engine.

Thanks! Couldn't agree more! I definitely just need to try it more rich than I have been running it... Do you know what your typical fuel flow/hr is?

 

[THEAirplanegirl]

Would someone be willing to explain to me the pressurizations you are suppose to be seeing/having in your cowing? I'll admit, this is something I am not super familiar with. I am assuming you want higher pressure running over the top of the engine than under? So that the air wraps over and around the back/down the cylinders and gets pulled out the back. I see a lot of bottom lip suggesting... so this extra area of lip helps to increase airflow?

 

[DENNY]

Do a Search on cowl pressure differential. Steve Pierce has some good write ups. Two simple low buck things to try would be moving that scat hose and blocking off the area around the oil cooler (aluminized tape for temp test). That big opening is allowing air to pressurize the lower cowl.
It took me a year and a half to get my temps down. Do one thing at a time and retest it will be worth it in the long run. Keep them cool with fuel until you get it sorted out.
DENNY

 

[skywagon8a]

Do a Search on cowl pressure differential. Steve Pierce has some good write ups. Two simple low buck things to try would be moving that scat hose and blocking off the area around the oil cooler (aluminized tape for temp test). That big opening is allowing air to pressurize the lower cowl.
It took me a year and a half to get my temps down. Do one thing at a time and retest it will be worth it in the long run. Keep them cool with fuel until you get it sorted out.
DENNY

Denny, My air filter is the large round one, like the later Cubs. There is supposed to be a baffle at the rear of it to prevent cold air from bypassing the filter into the area below the engine. Just as an experiment, I did not install this baffle. I have no cooling issues with either oil or CHT. On really hot summer days, I have seen a CHT rise above 400. In that case, I just pushed the mixture control richer to get it below 400. Oil temp, never over 190. Rear mounted oil cooler. That knowledge leads me to question how effective your aluminized tape is? My thinking is, there is too much bypassing leakage from the top to the bottom of the engine. One place to look would be the area around the nose of the engine behind the ring gear. There is a big hole there.

 

[RaisedByWolves]

Denny, My air filter is the large round one, like the later Cubs. There is supposed to be a baffle at the rear of it to prevent cold air from bypassing the filter into the area below the engine. Just as an experiment, I did not install this baffle. I have no cooling issues with either oil or CHT. On really hot summer days, I have seen a CHT rise above 400. In that case, I just pushed the mixture control richer to get it below 400. Oil temp, never over 190. Rear mounted oil cooler. That knowledge leads me to question how effective your aluminized tape is? My thinking is, there is too much bypassing leakage from the top to the bottom of the engine. One place to look would be the area around the nose of the engine behind the ring gear. There is a big hole there.

I made a baffle behind the flywheel, and it didn’t make a difference on cht’s. Took that baffle off behind the air filter. No difference. Made some holes in the lower cowl on the scoops, that helped slightly. Covered those scoops up and that hurt. Seaplane lip helped slightly. Took out the high compression pistons and that helped a lot. I’d still like to try moving the oil cooler like Pete did, but my temps are within 16 degrees.

 

[DENNY]

Denny, My air filter is the large round one, like the later Cubs. There is supposed to be a baffle at the rear of it to prevent cold air from bypassing the filter into the area below the engine. Just as an experiment, I did not install this baffle. I have no cooling issues with either oil or CHT. On really hot summer days, I have seen a CHT rise above 400. In that case, I just pushed the mixture control richer to get it below 400. Oil temp, never over 190. Rear mounted oil cooler. That knowledge leads me to question how effective your aluminized tape is? My thinking is, there is too much bypassing leakage from the top to the bottom of the engine. One place to look would be the area around the nose of the engine behind the ring gear. There is a big hole there.

I agree it may not help but, it is a simple cheap thing to check. I really do think the major issue is not enough fuel for this engine in this plane. I am just trying to come up with the simple fix before we start talking about the size of cheek opening. Closing up the front of the area behind the ring gear is not a bad ideal either. That scat hose intrigues me also, I would just take it out and dress warm to see if it has any effect.
DENNY

 

[DENNY]

I made a baffle behind the flywheel, and it didn’t make a difference on cht’s. Took that baffle off behind the air filter. No difference. Made some holes in the lower cowl on the scoops, that helped slightly. Covered those scoops up and that hurt. Seaplane lip helped slightly. Took out the high compression pistons and that helped a lot. I’d still like to try moving the oil cooler like Pete did, but my temps are within 16 degrees.

I have a big cooler behind #4 and while it works great (I have blocking plates in most of the time) It is a major PIA to work on anything on the back the engine with the cooler in the back. Simple things like Filter change, Mag checks, and leak inspection just suck with the cooler in the back.
DENNY