New Engine/High CHT

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JOhnH

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It has been about 6 weeks since my C172 blew an engine and we landed on the highway. I went up with the mechanic for the first time today. All went well except that the engine analyzer reported the #3 cylinder reached 470 degrees on climb out. He was the PIC (actually he was the only pilot because my wife, the usual pilot, was at work) The engine analyzer started flashing at 450 and he kept climbing to 2500 ft before leveling off. The CHT for the back cylinders (#3 & #4)then dropped to aobut 420 for the duration. Cylinder #4 was close behind but the analyzer only shows the hottest cylinder while the warning is flashing.

Will a few minutes at that temp during breakin cause any lasting damage in a 180 HP O360? The mechanic I flew with (who repaired the wing), AND the mechanic that replaced the engine assure me that it is not a problem and I trust them, but as Ronald Reagan said "trust but verify".

Thanks,
John
 
This was the first flight after overhaul, or with a new engine, right? I've seen this happen before -- to me. CHT's will be very high on initial climbout on the first flight due to the friction of the new rings against the new cylinder walls as the metal is worn to match and the rings "seat" themselves. This is especially true if the engine wasn't run much for testing after assembly. In fact, it is the drop in CHT to normal values as the friction abates that tells you the engine is "broken in." Only if this abnormally high CHT continues beyond a few hours do you have a real problem.
 
JOhnH said:
It has been about 6 weeks since my C172 blew an engine and we landed on the highway. I went up with the mechanic for the first time today. All went well except that the engine analyzer reported the #3 cylinder reached 470 degrees on climb out. He was the PIC (actually he was the only pilot because my wife, the usual pilot, was at work) The engine analyzer started flashing at 450 and he kept climbing to 2500 ft before leveling off. The CHT for the back cylinders (#3 & #4)then dropped to aobut 420 for the duration. Cylinder #4 was close behind but the analyzer only shows the hottest cylinder while the warning is flashing.

Will a few minutes at that temp during breakin cause any lasting damage in a 180 HP O360? The mechanic I flew with (who repaired the wing), AND the mechanic that replaced the engine assure me that it is not a problem and I trust them, but as Ronald Reagan said "trust but verify".

Thanks,
John
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sounds normal to me..Ive seen temps in the 500's on breakin flights. then out of no where they are back in the mid 300's..
 
Thanks for the comments. I am starting to feel a little better about it.

Part of my nervousness is that my old engine had about 1700 hrs, and the #4 cylinder routinely reached 450-460 CHT on climb. It was fine after that. I was told not to worry about it, but when the old engine blew, it was #4 that had the piston rod sticking out the top.

This new engine was run on a test stand for about 3 hours before delivery, and my mechanic had it up twice before I went up for a total of about 3 more hours. Our 1.5 hours today puts about 7.5 hours on it. We plan to take it up again on Thursday.
 
taters said:
sounds normal to me..Ive seen temps in the 500's on breakin flights. then out of no where they are back in the mid 300's..
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:yikes: I would definitely never ever fly in the 500s no matter if you're breaking in the engine or not. Slightly higher CHTs are to be expected, but not CHTs that are way above TCM's already way-to-high red line.

Seems like much better to break the engine in slowly instead of trial by fire....I wouldn't blindly trust most mechanics when it comes to their opinion on what engine temperatures are ok. 420 for a bit during break-in sounds borderline ok, but I'd expect trouble if you run at >500 for even 10 minutes (and that trouble might not appear for a while). This delay is problematic, too, because you won't be able to link the problems later to this flight and to this mechanic.....

-Felix
 
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I wonder what climb speed was used, you do not have to climb at vx. Go for a flat climb rate unless it is somehow unsafe to do so. You really want good airflow over those jugs the first few hours.
Also, if it applies to this carb (Tom?), leave it at wot for best fuel delivery (enrichment valve).
If temps exceed redline, there is something wrong, or something being done wrong imo.
 
JOhnH said:
Thanks for the comments. I am starting to feel a little better about it.

Part of my nervousness is that my old engine had about 1700 hrs, and the #4 cylinder routinely reached 450-460 CHT on climb. It was fine after that. I was told not to worry about it, but when the old engine blew, it was #4 that had the piston rod sticking out the top.

This new engine was run on a test stand for about 3 hours before delivery, and my mechanic had it up twice before I went up for a total of about 3 more hours. Our 1.5 hours today puts about 7.5 hours on it. We plan to take it up again on Thursday.
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I agree with Felix, 500 is way too high, even for a break in. With a broken-in engine you should never see anything above 400F and if you see one going above 380 you should do something to cool it down. During break-in CHTs can and do spike a bit but I'd be surprised to see anything above 420 and if one goes above that I'd immediately level off unless there was a serious safety issue doing so.

But with 6+ hours on your engine the rings should have been well seated a long time ago unless you have chrome cylinders. In any case, given the airplane's history of high CHTs I'd take a good look at the baffling to see why things are so hot before further flight.

Also, you don't happen to have a plug gasket CHT probe on the offending cylinder do you? They tend to run 20-30F hotter than plugs attached to the CHT boss under the cylinder heads. The lower plug tends to read hotter than the top plug as well.
 
Ron Levy said:
This was the first flight after overhaul, or with a new engine, right? I've seen this happen before -- to me. CHT's will be very high on initial climbout on the first flight due to the friction of the new rings against the new cylinder walls as the metal is worn to match and the rings "seat" themselves. This is especially true if the engine wasn't run much for testing after assembly. In fact, it is the drop in CHT to normal values as the friction abates that tells you the engine is "broken in." Only if this abnormally high CHT continues beyond a few hours do you have a real problem.
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IAW post 4 "This new engine was run on a test stand for about 3 hours before delivery,"

Every thing that you suggest as a reason for high temps should have happened on the cell. This engine was 3 hours into its life as a fresh overhaul, and should have been operated IAW the Lycoming instructions given in their operators manual

It seems a bit shame full of the A&P to over temp the new engine on the first flight and blame it on the newness.

It requires about 15 minutes on the cell to seat a set of rings, so all that was accomplished in this case was destruction of the rings by over heating them and removing the temper and causing them to collapse into their piston grooves and allow high oil consumption and low compression.

IMHO any engine that was tested IAW the manufacturers instructions on a cell is already is broke in and should be run normally as given in the engine operators manual
 
JOhnH said:
It has been about 6 weeks since my C172 blew an engine and we landed on the highway. I went up with the mechanic for the first time today. All went well except that the engine analyzer reported the #3 cylinder reached 470 degrees on climb out. He was the PIC (actually he was the only pilot because my wife, the usual pilot, was at work) The engine analyzer started flashing at 450 and he kept climbing to 2500 ft before leveling off. The CHT for the back cylinders (#3 & #4)then dropped to aobut 420 for the duration. Cylinder #4 was close behind but the analyzer only shows the hottest cylinder while the warning is flashing.

Will a few minutes at that temp during breakin cause any lasting damage in a 180 HP O360? The mechanic I flew with (who repaired the wing), AND the mechanic that replaced the engine assure me that it is not a problem and I trust them, but as Ronald Reagan said "trust but verify".

Thanks,
John
Click to expand...

Do your self a favor, get the A&P to sign a letter that he operated the aircraft for ________ minutes at a higher temp than allowed by the manufacturer.

and when the engine has high oil consumption you can get him to change the cylinders for free, then keep good records on oil consumption.
 
taters said:
sounds normal to me..Ive seen temps in the 500's on breakin flights. then out of no where they are back in the mid 300's..
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How's it feel to shorten the life of an engine because you can't read the engine manufacturers engine operators manual?


Flying a new engine at high power settings, does not mean to over temp it.
 
JOhnH said:
Part of my nervousness is that my old engine had about 1700 hrs, and the #4 cylinder routinely reached 450-460 CHT on climb. It was fine after that. I was told not to worry about it, but when the old engine blew, it was #4 that had the piston rod sticking out the top.
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High CHT's on your Lycoming engine are associated with valve guide problems. If you "routinely" get CHT's up over 450 in the climb, you should take a look at the baffling, and also check for excess flash between the cooling vanes on the cylinder head. Performing the SB388 valve guide wear check periodically as recommended by Lycoming would also be wise.
 
Ron Levy said:
High CHT's on your Lycoming engine are associated with valve guide problems. If you "routinely" get CHT's up over 450 in the climb, you should take a look at the baffling, and also check for excess flash between the cooling vanes on the cylinder head. Performing the SB388 valve guide wear check periodically as recommended by Lycoming would also be wise.
Click to expand...

He should also have his Airspeed indicator checked, he may be holding the nose higher than he thinks.
 
gismo said:
I agree with Felix, 500 is way too high, even for a break in. With a broken-in engine you should never see anything above 400F and if you see one going above 380 you should do something to cool it down. During break-in CHTs can and do spike a bit but I'd be surprised to see anything above 420 and if one goes above that I'd immediately level off unless there was a serious safety issue doing so.
Click to expand...

Lycoming Service Instruction 1427B details recommended break-in procedures. They seem to work pretty well, at least they did on the cylinders on my left engine.

It is worth noting that 500F is the limit on those cylinders, so anything higher and you're exceeding the manufacturer-specific limits which a very bad idea. Note: limits are not goals and should not be treated as such. This is commonly confused. If you see over 500F, you definitely need to cool things off. Really you should be cooling off if you're seeing anywhere close to it. However, note that the recommended limits for maximum service life are 435F in climb and 400F in cruise. Engine installations being what they are, your temps may be very different. For example, Ed has a hard time getting his CHTs to 400F in his Comanche. My Aztec, with virtually the exact same engines, has a hard time keeping the CHTs below 400F, and this is with freshly redone baffles. The Aztec just has a horrid cooling design.

Like Lance, I try to keep my CHTs at or below 380. However on break-in on the cylinders on my left engine, I was seeing 430-450F at the recommended manifold pressure/RPM settings with a nice and rich mixture (not full rich, but full cowl flaps), and this included leveled off. I watched the cylinders break in as the CHTs dropped, and now they're as happy as the right ones. The right engine has 1750 hours on the genuine Lycoming cylinders, burns hardly any oil, and has compressions in the 70s. I know for a fact that I used to run it horridly before I had my engine monitor, and the previous owners did the same. CHTs were routinely very high, and those cylinders still seem to work so far.

To be fair, I did have to change the cylinders on the left engine (which was operated same as the right, and had better baffling) at 650 hours. However, they were Superiors that came with the plane, and one can decide for one's self whether that makes a difference in quality or not.
 
sba55 said:
And Lycoming clearly understands how their engines should be run :dunno:
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I'd listen to Lycoming more than I'd listen to some guy running a horse that tends to trash talk them instead of contributing useful engine knowledge. You win with knowledge - not with abuse.
 
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taters said:
sounds normal to me..Ive seen temps in the 500's on breakin flights. then out of no where they are back in the mid 300's..
Click to expand...


I was breaking in a cont TN-IO-550 w/RAM cylinders on a A-36 .It only lasted for about 15 seconds...put the fuel pump on high and it shot right down to something more reasonable. Obviously continuous operations at 500+ is going to melts things. I believe a piston loses half its strength above 400 For normal ops I dont let anything get above 390. I am a big fan of the Lycoming break-in procedure even on Continentals.
 
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One of the structural engineers on the Beechlist did a pretty elaborate explanation of the metallurgy used by the main cylinder manufactures and pointed out that metal began to lose it's strength in the just above 400 degrees F. There were some variables like probe type, location and different parts of the cylinder heating differently, but the point was, much above 400 for very long just isn't good. This break in does not sound normal to me. I'd be talking to another expert to get an independent opinion.

All that said, I don't pretend to know what Ted and some others know, but I have operated two turboed AC past TBO and am still running the 58P. The folks in Ada recommend 380 for a reason and have done an number of tests; they do say up to 400 and slightly higher in some short instances may not shorten cylinder life, but repeated exposure to higher temps will lead to shorter life. I know some engines like Teds may have some differences, but mid 400s will not lead to normal cylinder life and 500 is just nuts.
The Advance Pilot's Seminar hits this pretty hard. It's how I've gotten to where I have on my last two planes.

Best,

Dave
 
Let's keep in mind that during break-in, temps up around 450 are not abnormal, especially in climbout, but those temps should drop pretty quickly as everything seats in. After that, you don't want to see anything over 400 in cruise or 435 in climb, and cooler is better. Finally, Lycoming is very insistent on compliance with the periodic SB338C valve "wobble" check to ensure that excessive valve guide wear (a known byproduct of high CHT's) is not occurring. Considering that excessive valve guide wear can lead to "necking" (thinning) of the valve stem, which in the worst case can result in release of the valve head and catastrophic engine failure, that's something you want to keep a good handle on.
 
Just an FWIW

I have had two tops overhauls done on my O320-D3G. Both times the CHTs were a little higher than normal. Both times the break in was flown during cool weather and the highest temp I ever saw, with both ECI Titans and Lycomings, was 405F and was only seen during climb out.
 
I don't know what aluminum alloy Lycoming uses (Axxx.x), but in general bad things are going to happen to alloys over 400F - tensile strength drops dramatically, dimensional stability goes to pot and the rate of crack propagation goes way up.
 
After chatting with someone more about his, the Lycomings seem to run a bit hotter at times. My experience is with fuel injected, large bore TCMs. The valves seem to take more heat in the Lycomings. Ron's remarks may be more on point.
But, most mechanics just fix stuff and don't have P.E.s or advanced degrees. It's up to you, the pilot and owner to understand how this works. In the instant case, I'd sure be asking someone that really knew this stuff. This sure doesn't sound normal to me.

Over the years, I've really gone back and forth with mechanics on some things. Early on as an owner, I listened to couple folks that in retrospect we're the sharpest knives in the drawer: not only did they cost a lot in money and downtime, they put me in some dangerous situations. Be careful who you deal with. On smaller, least complex engines, it's not brain science, but still has to be done right. These folks had been referred to me by other owners happy with their work.

I once had a guy put in cylinders that had the skirts hit the crankshaft and wonder what was making the noise. When I asked if he had speced the cylinders before installing them: I got the old, I've been doing it this way for years and it's always worked. Well, that started a big recall on ECI cylinders that had a manufacturing defect. If he would have speced the cylinders, he would have caught that. Instead, I had bad cylinders installed and he had to replace them all and several other things where damage resulted. There were other issues also.

They all will take your money: it's up to you to make sure it's well spent.

Best,

Dave
 
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