my53cad

my53cad

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My #3 CHT exceeds 400 degrees on every normal takeoff. I have added washer, directed more air over #1 to #3 cylinder, and blocked off airflow through oil cooler. My oil temp is now normal in the 180 to 185 degree range but #3 CHT is still exceeding 400 degrees. I know I can lower the nose and stop the CHT climb, but #3 still climbs to as high as 420 degrees in warm weather. Once I am above about 3000 feet, my CHT is back down below 400 even with full power and then proceeding with a normal climb. I am now considering a cowl flap from Aerosplat. Does anyone have any experience with the new Aerosplat cowl flap and do you think it will help the problem? By the way, I have 1 Lightspeed Electronic and 1 Slick mag and the timing has been checked and adjusted as it should be from Manufacturers specifications!
 
I added two cowl flaps with great success. I find them helpful during high DA and high oat takeoffs. Before you add a cowl flap be sure to clean up the exit air flow with a lower firewall bump.
 
rph142 said:
I added two cowl flaps with great success. I find them helpful during high DA and high oat takeoffs. Before you add a cowl flap be sure to clean up the exit air flow with a lower firewall bump.
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Okay, I'll bite. What the heck is a lower firewall bump!
 
It’s a curved piece of metal added to the lower firewall where the air exits. The goal is to accelerate the air as it exits the cowling. It dropped my cht’s by around 10f.
 
400 on isn't necessarily a cause for concern, nor is 420 for a short period. And it's not particularly unusual on climb-out with these planes.
Or so I believe, after watching/reading dozens of videos/articles and the Lycoming engine operation manual, and having much the same experience for 1700+ hrs with my plane (with the baffle bypass on #3).
 
rv6n6r said:
400 on isn't necessarily a cause for concern, nor is 420 for a short period. And it's not particularly unusual on climb-out with these planes.
Or so I believe, after watching/reading dozens of videos/articles and the Lycoming engine operation manual, and having much the same experience for 1700+ hrs with my plane (with the baffle bypass on #3).
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+1. Mike Busch, who is more conservative than Lycoming, considers 420 the top of an imaginary “yellow arc” for continuous operation. There’s no authoritative source I’m aware of that would even blink at 420 in the climb to 3,000.
 
my53cad said:
My #3 CHT exceeds 400 degrees on every normal takeoff. I have added washer, directed more air over #1 to #3 cylinder, and blocked off airflow through oil cooler. My oil temp is now normal in the 180 to 185 degree range but #3 CHT is still exceeding 400 degrees. I know I can lower the nose and stop the CHT climb, but #3 still climbs to as high as 420 degrees in warm weather. Once I am above about 3000 feet, my CHT is back down below 400 even with full power and then proceeding with a normal climb. I am now considering a cowl flap from Aerosplat. Does anyone have any experience with the new Aerosplat cowl flap and do you think it will help the problem? By the way, I have 1 Lightspeed Electronic and 1 Slick mag and the timing has been checked and adjusted as it should be from Manufacturers specifications!
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What are the other CHT's doing? Is it only that one? What is that EGT? Perhaps a dirty injector causing a lean mixture in #3.....?
 
Brian is asking good questions, and I have more to ask. Fuel injections or carb? What are the other cylinder's CHTs? What is the EGT doing when the CHT is higher than you would like? We need that information to see if fuel flow may be contributing. Has it always done this, or is it something new? Have you tried swapping the CHT probe with another cylinder to rule out that it's just an indication issue?

Your oil temps are just a bit cooler than normal (depending on the season & weather), so there still may be excess air going through the oil cooler that's not being used to cool the cylinders directly. What airspeed is your typical cruise-climb? Are there any obstructions (i.e. a large heater muff) at the cowling exit that may be preventing air to exit? Are you sure you have all the cracks and gaps sealed on the baffles and/or plenum? Even a few gaps can make a big difference, but that will usually affect all the cylinders rather than just one. The same goes for timing changes.
 
D-Dubya said:
Brian is asking good questions, and I have more to ask. Fuel injections or carb? What are the other cylinder's CHTs? What is the EGT doing when the CHT is higher than you would like? We need that information to see if fuel flow may be contributing. Has it always done this, or is it something new? Have you tried swapping the CHT probe with another cylinder to rule out that it's just an indication issue?

Your oil temps are just a bit cooler than normal (depending on the season & weather), so there still may be excess air going through the oil cooler that's not being used to cool the cylinders directly. What airspeed is your typical cruise-climb? Are there any obstructions (i.e. a large heater muff) at the cowling exit that may be preventing air to exit? Are you sure you have all the cracks and gaps sealed on the baffles and/or plenum? Even a few gaps can make a big difference, but that will usually affect all the cylinders rather than just one. The same goes for timing changes.
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Next set of questions .. if fuel injected, have you done the “GAMI” spread (sounds oddly obscene…) ? Your #3 cylinder might be running lean, the solution would be to upsize the insert orifice a few thousands of an inch. (Also obscene…)
 
I appreciate all the information. I have the 150 HP low compression Lycoming engine and I would normally climb at about 100 kts. The #3 cylinder is the only one that tops 400 degrees and the next hottest cylinder is usually #1 which is on the same side and runs 20 to 25 degrees cooler. I have the Sam James Cowl with the plenum and it is all sealed up nicely. Last Condition Inspection in October, all cylinders were at 76-78 compression including #3. Aircraft and engine have about 920 hours.
 
Still some questions related to fuel & EGTs that were asked but left unanswered. Look those over and let's see if we can help you zero in on the issue.
 
Just for more information, I sent a timelapse to Savvy Aviation and they sent me back a report that for a carbureted engine it had the most even fuel flows that they had seen on a carbureted engine from takeoff through climbout.:confused:
 
Okay, I guess I'll be a bit less subtle...
  1. Has it always done this, or is it something new?
  2. Have you tried swapping the CHT probe with another cylinder to rule out that it's just an indication issue?
  3. Are there any obstructions (i.e. a large heater muff) at the cowling exit that may be preventing air to exit?
  4. Have you done the “GAMI” spread? Your last post said it's carbureted, but this is still a good test to make at altitude.
Is this a Sam James plenum, or one of your own design? Home-spun versions can sometimes have unexpected results.
What's your fuel flow during a max power takeoff?
You stated that the time is set per manufacturer's specs...is that 25 degrees BTDC or something else?

And to answer your question on the baffle bypass, Dan Horton has an extremely good write-up with pics on how to increase airflow around the partially-obstructed fins at the back of the #3 cylinder. While it's more work than putting a washer back there, it's an elegant and effective solution to solving the hot #3 cylinder. It's what I did at the recommendation of an EAA Tech Counselor and it worked like a champ. Take a look and see if you think it might help, as Dan walks you through the whole issue in this post: https://vansairforce.net/threads/baffle-mod.37835/
 
D-Dubya said:
And to answer your question on the baffle bypass, Dan Horton has an extremely good write-up with pics on how to increase airflow around the partially-obstructed fins at the back of the #3 cylinder. While it's more work than putting a washer back there, it's an elegant and effective solution to solving the hot #3 cylinder. It's what I did at the recommendation of an EAA Tech Counselor and it worked like a champ. Take a look and see if you think it might help, as Dan walks you through the whole issue in this post: https://vansairforce.net/threads/baffle-mod.37835/
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+1 on the baffle duct mod; it was a fairly easy task, a coupla hours playing with sheet metal and RTV, but the payoff was obvious and immediate, 15-20⁰ cooler CHT on my pesky warm #3.
 
my53cad said:
By the way rv6n6r. What is the baffle bypass?
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Someone already answered that so I won't repeat it - but you said you "added washer" in your OP, so I assumed you meant an alternate method some people have to provide bypass air by sticking a washer in there. At any rate I would definitely recommend adding the bypass duct per Horton's write-up.
 
Added a washer? Try adding 2 or 3 washers.. one isn’t enough. Also 100 knots on initial climb is too slow.. get it to 110 to 120 knots. The extra airspeed also allows your prop to make more RPM.
 
I agree with Tom on the climb speed. I may do 100 knots if I really need to climb quickly, or possibly until I reach 750' or 1000' AGL, but 120 knots IAS is what I usually target. It's a good compromise between climb rate and engine cooling, especially in warmer climates.
 
Check for casting flash in the fins on #3's head. Should be other posts here w/pictures.
Look hard for leaks. Every square mm of leak is air that didn't go thru your cooling fins. Common easy to miss spots: #3 at base of cylinder to rear baffle. #4, similar spot.
How well does the snorkel air inlet seal to the carb air box? Every bit of air that sneaks thru there pressurizes the lower cowl, reducing flow thru your fins.
Are the inlet ramps (fiberglass on upper cowl) installed?
Are the conical gussets installed that lead from the cowl openings up to #1 and #2?
Look for dust marks on your upper cowl from leaks around the baffle fabric.
 
The 425 number may come from Mahlon and probably others. It is only valid until the rings are seated. Mahlon years ago stated that he had never seen evidence that temps up to 425 have any detrimental long term effect.
issues that I have never seen mentioned:
The baffle portion that goes around the oil pressure relief valve is difficult.
Long ago there was talk about wrapping the hot cylinder intake tubes on carb engines on the theory that it will keep the fuel cooler.
Lycoming's position years ago was that anything up to red line was ok for CHT. They have since published recommended numbers for continuous.
 
my53cad said:
My #3 CHT exceeds 400 degrees on every normal takeoff. I have added washer, directed more air over #1 to #3 cylinder, and blocked off airflow through oil cooler. My oil temp is now normal in the 180 to 185 degree range but #3 CHT is still exceeding 400 degrees. I know I can lower the nose and stop the CHT climb, but #3 still climbs to as high as 420 degrees in warm weather. Once I am above about 3000 feet, my CHT is back down below 400 even with full power and then proceeding with a normal climb. I am now considering a cowl flap from Aerosplat. Does anyone have any experience with the new Aerosplat cowl flap and do you think it will help the problem? By the way, I have 1 Lightspeed Electronic and 1 Slick mag and the timing has been checked and adjusted as it should be from Manufacturers specifications!
Click to expand...
I had the same problem with my RV7A. I installed a cowl flap from AntiSplat and it solved my problem. The cowl flap is well designed and easy to install.
 
Cheaper... is the louver kit from Van's. $21 vs. $399
Made a difference on an O-360 where we had exhausted ideas.
 
JonJay said:
Well, you now have lots of cures looking for a problem I personally don’t think you have, but that’s for you to decide.
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Kinda depends on OP's definition of 'warm weather'. If that's 80F it'll make the plane pretty problematic in Texas, AZ, etc. If 'warm weather is 100F, I agree, it's pretty much as good as it'll get.
 
Hey D-Dubya. Just trying to answer some of your questions. The #3 CHT has always been that way. I switched probes with another cylinder and also bought a new one from Spruce but the temp stayed the same. No obstructions such as ductwork or anything like that. It is a Sam James Cowl with the plenum and it is carbureted. Timing is set at 25 degrees BTDC. I will have to note the fuel flow next time I fly. I will pay closer attention to the clearance on #3 cylinder on back side next time I have the plenum off. The baffle bypass looks like an interesting idea but it might take me a while to do that. Maybe I will just set my alarm to warn me when the temp gets to 410 degrees instead of 400 degrees and see how that works for now. Thanks very much for the ideas!!
 
D-Dubya said:
Brian is asking good questions, and I have more to ask. Fuel injections or carb? What are the other cylinder's CHTs? What is the EGT doing when the CHT is higher than you would like? We need that information to see if fuel flow may be contributing. Has it always done this, or is it something new? Have you tried swapping the CHT probe with another cylinder to rule out that it's just an indication issue?

Your oil temps are just a bit cooler than normal (depending on the season & weather), so there still may be excess air going through the oil cooler that's not being used to cool the cylinders directly. What airspeed is your typical cruise-climb? Are there any obstructions (i.e. a large heater muff) at the cowling exit that may be preventing air to exit? Are you sure you have all the cracks and gaps sealed on the baffles and/or plenum? Even a few gaps can make a big difference, but that will usually affect all the cylinders rather than just one. The same goes for timing changes.
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Hey David. I also have at least half of the oil cooler covered with 300 MPH aluminum tape. Before that my oil temp was down around 155 degrees in cruise and 165 degrees with full power on takeoff. Yikes! Maybe I should cover more of the oil cooler.
 
The Lycoming recommended max CHT for continuous operation is 435. Busch recommends 420. Bush also recommends 350 minimum for cruise. Installing louvers will likely put you below 350, especially in cooler weather.
A cowl flap provides better control over this. A louver does not provide that option.
My first choice would be to simply go with what you have.
If you do a lot of flights above 8000' that is another reason to leave things alone.
Apples to oranges but Busch talks about Continentals. A Continental GO 520 in the desert will go to the red line on both oil and cylinders and there is absolutely no way to lower this on the ground. Think taxi from the SW corner to the NW corner at Phoenix at 110 F ambient. The first time the temps will drop will be when the airplane accelerates to cruise.
My vote is to disconnect the CHT warning and move on.
Keep in mind that many of the normally aspirated engines in the 70's and earlier had no CHT instruments. No CHT, no worries.
 
jrs14855 said:
The Lycoming recommended max CHT for continuous operation is 435. Busch recommends 420. Bush also recommends 350 minimum for cruise. Installing louvers will likely put you below 350, especially in cooler weather.
A cowl flap provides better control over this. A louver does not provide that option.
...
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cover the louver with 300 mph aluminum tape in the winter.

I also need to add that I'm aware of an RV where they installed the cowl flap and didn't see much CHT improvement. Rather a bummer for the $$$.
 
my53cad said:
Hey D-Dubya. Just trying to answer some of your questions. The #3 CHT has always been that way. I switched probes with another cylinder and also bought a new one from Spruce but the temp stayed the same. No obstructions such as ductwork or anything like that. It is a Sam James Cowl with the plenum and it is carbureted. Timing is set at 25 degrees BTDC. I will have to note the fuel flow next time I fly. I will pay closer attention to the clearance on #3 cylinder on back side next time I have the plenum off. The baffle bypass looks like an interesting idea but it might take me a while to do that. Maybe I will just set my alarm to warn me when the temp gets to 410 degrees instead of 400 degrees and see how that works for now. Thanks very much for the ideas!!
Click to expand...
As others have said, the CHTs you list are not really that bad. But I understand that "one of these things is not like the other" and it bothers you. I get it, and I'm guilty of it...many, many times. Here are a few thoughts based off your answers:
  1. Mike Busch has a good webinar titled "How Hot is Too Hot?" It's worth an hour of any pilot's time to watch it.
  2. You could shift the timing on both ignitions to be closer to 23 degrees BTDC and make some temperature gains across the board without losing any noticeable power on takeoff. We're Experimental and it's perfectly legal and safe to do this.
  3. Shifting the alarm point in your EFIS will prevent a distracting alarm on takeoff. I originally had my yellow caution range from 380 to 400 and the red warning range above that. On a hot day, that alarm would pop up right after I cleared the end of the runway. 200' AGL is not where you want to be pushing over the nose to improve cooling. After much reading and digging around, I realized I could shift the yellow range from 400 to 420 and it's not hurting anything. Your setup may be slightly different, but you get the idea.
  4. The Dan Horton bypass thing does take a little time, as there's some disassembly and peeling back RTV involved. But it's not difficult, and should only take an afternoon or so to knock out. If the temp issue is bothering you, it's a low-cost and low-risk thing to do. However, removing the washer or two behind #3 and moving that baffle forward may affect how the plenum fits. Look before you leap.
  5. It still sounds to me like there's a lot of air going through the oil cooler that should be going past the cylinders. Is it possible the cooler is oversized? If you're sure your oil temps are correct, it may be worth putting in a damper on the oil cooler. Most people do it to get the oil temps up in cooler weather, but some on this forum have stated that they close off the oil cooler (partially or fully) during take off to get all of the air going over the cylinders for the climb to pattern altitude. It takes several minutes for the oil temps to climb, but by then they can open the damper back up after reducing power to a cruise/climb setting. Of course, that's one more knob to fiddle with, one more thing to fail, etc. But it's what some have done on here and it works.
  6. Are you absolutely, positively sure that the plenum and baffles are well sealed? It's very easy to miss gaps, especially around the inter-cylinder baffles underneath and where the baffle "tabs" have gaps around the cylinder bases. Some people mistakingly think that it's supposed to be that way and leave those gaps as they are (I was one of those people). Any gap, crack or leak is allowing air to bypass the cylinder cooling fins and lowering the differential pressure from top to bottom. Again, I was one of those that couldn't conceive how a few gaps would really make any difference at all, but I was proven wrong. I would suggest having another set of knowledgeable eyes look over your baffles, along with several different types of flashlights that you can poke around and drop into place between the cylinders. When you see light shining through gaps from underneath, it's somewhat of an eye-opener. No pun intended. It can be tricky reaching those hard-to-get spots. A piece of 1/4" tubing shoved in the tip of an RTV tube works, as does putting a glob of RTV on a short dowel rod and sticking it up where it needs to go.
  7. Lastly, the cowl flap thing is an option, but that involves altering painted surfaces and more expenditures. It's somewhat of a last ditch option. I'd try at least some of the other stuff listed above first--I'll betcha your temps come down by at least 20 degrees after just a few of these changes.
 
#3 is normally the hottest cylinder, what are thoughts on raising oil pressure to highest recommended pressure?
 
There is a thread that discusses why #3 runs hot. DanH does a great job explaining the why. I went with a bypass duct after I looked at the casting since the fins were completely blocked AND I’m in the building stage, not flying yet. If I was flying, I would use a washer if #3 was running hot.

Baffle Mod

Lycoming cylinders have a classic baffle problem. I don't know if anyone else has taken this particular approach to solving it (lots of ways to skin a cat), but maybe the pictures will help the new guys understand the issue. Here's the root of the problem. The intake side of the head has no...
vansairforce.net vansairforce.net
 
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