Cherokee 180 Break-In CHT Cylinder Head Temperature Guidance

help please ... I searched the all-time archives and I can't find a great article on the topic of cylinder break-in and expected temperatures. We'll ask some partner/sponsors like JPI but in the meantime, advice for Kay would be appreciated, and we'll aggregate that advice and put it into the magazine.

Digital Product Manager
Piper Owner Society


  • You should expect to see higher temperatures as that cylinder breaks in. Try to avoid having the CHT above 420 degrees for any extended period. Follow the same break in as you would all new cylinders. 75% for the first hour then 65% for the 2nd hours. From then on fly it normally for the next 10 to 20 hours maintaining cylinder temps at or below 400 degrees. Happy flying!

  • I don't have my Lycoming books handy, but here's the guidance Continental gives regarding what you can expect to see as your cylinders "break in." The Lycoming guidance is essentially similar. CHT will drop for up to 15 hours; once it hits the final steady state number, your rings are fully-seated.

    One other thing to keep in mind is that making an accurate absolute temperature measurement in an engine compartment is very challenging, and that's why the engine makers don't give you a whole lot of numbers for your verification purposes. The EGT/CHT probes JPI sells produce only 20 microvolts of signal for every 1 degree Fahrenheit. In most CHT applications this only an inch from the kilovolt-class ignition signal (eight orders of magnitude higher!), then it runs through 20 feet of low-grade wire to a measurement unit that sees temperatures from well below zero to well over 100 degrees. And as a result, no engine monitor guarantees its accuracy.

    At one point I was curious about the accuracy of my own monitor, so we pulled all the thermocouples, placed then in a calibrated digital laboratory oven, and made some recordings. With the oven set to 400F, our probe readings were anywhere from 358 to 433 - a pretty big error. Calibration of the monitor brought this in some, but within a few days the numbers had drifted to almost as bad as our originals.


  • edited October 2022

    Kay, the advice on the forum is generally sound, but no one knows more about your engine than the people who design, build, test, and inspect them every single day…..Lycoming. They have wonderful publications including proper break-in procedures.

    Lycoming favors judging ring seating not by CHT behavior but by oil consumption stabilization. So many factors unrelated to the actual cylinder itself affect indicated CHT including aircraft attitude, baffle condition, OAT, and as Seneca38173, Bob, pointed out, the accuracy of the measurement system itself.

    You might find the following helpful:



  • This is a great discussion and we've already learned alot from Mike J Jones and Bob (Seneca38173). However, when you overhaul an engine it comes with a manual from the overhauler (usually produced by the manufacturer). When I've overhauled my TSIO-360's it has always come with procedures for breakin.

    In my opinion Mike's advice is right on the money. Our knowledge and information is good but only the manufacturer's or overhauler's advice should be followed. As you know, overhauling an engine is hugely expensive. If one of our members should give you advice, which you follow, which results in a problem or failure of the engine, I think you would be very upset. While we're all very knowledgeable and we mean well, we're not pro's on this subject. Check with your overhauler or manufacturer.

    Scott Sherer
    Wright Brothers Master Pilot, FAA Commercial Pilot
    Aviation Director, Piper Owner Society Forum Moderator and Pipers Author.

    Need help? Let me know!

  • Thanks for the feedback but I still have a problem that's not being addressed. First off, my oil consumption, after one quart during break-in, is back to normal. However, my head temperature is still way out of whack! Take a look at this image. This is at 9 hours. I climbed out at 100 feet per minute yesterday (shallow), and the outside temp was 42 degrees. So without saying it, but still saying it, is that if I'm not consuming oil then I'm good. Without the guidance of normal temperatures during the first xxx hours, how could I possibly know if this is normal or if I'm burning up another cylinder? In my opinion, this should NOT be this hot after 9 hours (BUT I DON"T KNOW FOR SURE). Had I kept full power and a climb in, this would have hit 440 degrees. I have a contact at Lycoming. I'm going to have them take a look at this thread. Even if there is a blurb like, "If your cylinder still is over 420 degrees on climb after 15 hours have it looked at," then at least we'd have a baseline of normal. Right now, I have none.

    I'll let you all know what Lycoming says but I welcome more feedback. I'd especially like to hear from anyone that has broken in a Lycoming cylinder before and how long it took them to see normal temps during climb and cruise.

    Thanks all!

  • This is a great post Kay, and your insight about what I'll call the "lack of objective & measurable information with which to gauge the health of my new cylinder," is right on the money! Many of us on the Forum, me included, often answer questions with, "but we've always done it that way." I'm glad you're pushing us to think outside the box!

    The technical pubs from the engine makers, describing oil and temperature stabilization as the goal, sound hand-wavy at best. But of course those pubs were written long before we all had engine monitors, and in the day when the makers were crawling with highly-experienced engineers and had lots of in-house expertise. Now, most engineering expertise is outsourced from DER consultants, like my friend at Penn State.

    But I do have to ask one question: when was your monitor calibrated, how was the calibration performed, and what was the residual error after calibration?



  • edited October 2022

    Kay, I read a bit about your background, experience, and the “information gap” you are experiencing and the frustration of so many opinions and perhaps contradictions. I understand.

    While “tribal wisdom” is sometimes helpful, it becomes less so when the designers and builders of the equipment are still available for consultation. You are doing the right thing by asking your Lycoming contact for the answer you are looking for.

    in the meantime, and since you asked, I do have experience in breaking in both a cylinder and an engine in my 1966 Cherokee 180 that I have flown and maintained for 34+ years. On those occasions I followed Lycoming’s break in instructions to the letter. Their “Operator’s Manual” for the O-360 series engine specifies a max cylinder head temperature of 500 degrees Fahrenheit. It adds a note saying that “For maximum service life of the engine maintain cylinder head temperature between 150°F and 400°F during continuous operation.” The KEY WORD in this note is ‘continuous,’ as in cruising along enjoying the scenery on your next cross country adventure. I would not be overly concerned with higher CHT during max RPM operations such as your takeoff climb as long as you stay within Lycoming’s published data.

    If you see higher readings (but within limits) during continuous operation, then you might wish to explore ways to reduce it, and nothing lowers CHT faster than reducing your cruise power. Lycoming recommends 65% power for example to extend engine life.

    Here is a link to the operation manual for what I believe is your engine. The data is on page 3-12. Click on the download button to retrieve it. I hope these comments are helpful.



  • edited October 2022


    A couple questions;

    Was the engine oil changed after the new cylinder was installed? If yes, was straight weight mineral oil put in the engine and additives (like Cam Guard) left out?

    Lycoming specifies straight weight mineral oil during break-in for the first 50 hours, or until oil consumption stabilizes, then switch to ashless dispersant oil (see Lycoming link below). In my experience (2 engine cycles), 9 hours is not enough time for full break-in. It doesn't matter that you're only breaking in 1 jug, it still needs to go through the full break-in procedure.

    My questions about oil are backtracking to the beginning for a reason. Troubleshooting involves eliminating variables, and the best method to determine root cause is to go back to the start.

    Bob (Seneca38173), Scott, and MikeJJ's posts contain excellent advice, and I'll add this: If the answers to my oil questions above are "yes" and "yes", here's a couple other things to check:

    Ensure there are no intake leaks and that all the bolts and intake tube couplers are tight, especially on the new jug. Check gaskets also. An intake leak will lean out that cylinder, and it may run hot as a result.

    Check ALL the baffling including the adjacent cylinder baffle. The block needs to be in place to prevent cooling air from bypassing the fins.

    Swap the sensor from the "hot" cylinder to a different cylinder. If the "hot problem" follows the sensor, then the sensor may be misreading. Bob posted that putting the sensors into a calibrated oven yielded a 75 degree difference in outputs. That's a difference too big to ignore.

    Jim "Doc Griff" Griffin
    PA28 - 161
    Chicago area

  • Thanks for all the comments! Unfortunately, not one person here has told me their Lycoming break-in head temperatures through the first 10 hours. I'd love to hear that experience. Lots of comments about oil, leaks, break-in, etc... Oil is mineral oil. Not burning much after one quart in two hours. My A&P is looking to swap probes to see if it's an instrumentation problem; thanks for the tip Jim!

    I've followed the break-in procedure precisely so that is not a problem but thanks for the input, no need to keep posting that.

    I'd like to ask everyone reading this a question:

    If you've broken in a new Lycoming cylinder in the past, do you know the head temperatures at that time and when they came down?

    I know for the next 60 years I'll be able to share this information with new aviators when they ask.



  • Kay, have mechanic double check timing of mags. With the rpm you are running, close to or over 80%, your carb should be into what is called the economizer circuit. Actually a misnomer because it actually ADDS more fuel at these power settings for cooling. Your egt seems high despite what looks like good fuel flow. I run 70% in my 172 H@AD and egts are only 1250's or so. From a breakin standpoint, low 400's might be seeable on the first couple hours but the trend should be down in each successive hour. I have rarely seen over 400 unless its a hot summer day on a ground run. Hit timing first. EAsy checks. I hesitate to speculate more as not up to date on your particular eng overhaul,


    48 yrs A/P IA DAL aircraft inspector. 172N

  • Kay, I just went through breaking a new motor from Lycoming and I had a problem with one cylinder where the temperature exceeded my 400 I try to stay below. Talking with Lycoming the tech rep basically said he wasn’t worried, he said keep it 450 degrees or below and you will be fine. After 120 hours #1 still runs hotter then the rest but now only reaches 410on climb out. Not sure if this helps?

  • Dtaglila, did lycoming send you the data from their test cell run on your new engine? Would be interesting to compare with what you see on your engine monitor. Bob

  • UPDATE: I flew to South Padre Island this week and the return trip was great. Taking off this morning for the first time, my cylinder head temperature rose to 420 and then started to drop through the entire climb. This is the best sign I've seen so far. Without leaning, the new cylinder would have been running at around 389. BUT, for the first time since getting the cylinder, I also leaned my mixture and the temp stayed under 420. So while still running hot, much improvement over the last two hours. At this point I'm expecting to see continued drops. I'll keep you posted! :)


  • Kay/sideslope;

    Great news, and very happy to hear! As I posted last week, I honestly didn't think 9-10 hours was enough time to break in a cylinder, but I also didn't have any hard evidence to back myself up, because different parts break-in at different rates. Even the exact same part on 2 identical engines may break-in differently (same for whole engines), so it can be very difficult to determine an exact time-frame when it will be complete.

    I believe the reason engineers at Lycoming or Continental give us power settings and a range of temps (with limits) to stay inside is because they understand the wide disparity in variables like outside air temp, air flow, fuel flow, baffling, etc., that will occur in the field. Basically, stay within the limits, and your break-in should be successful. That's my opinion as an engineer, and my opinion plus $6.50 will buy you a gallon of Avgas. 😂

    In any case, we are glad to hear your engine is running well, and that you're back punching holes in the sky!

    Thank you for updating us!

    Happy flying!

    Jim "Doc Griff" Griffin
    PA28 - 161
    Chicago area

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