High O-360 CHT's

By reaching out on this Piper forum, I am hoping someone will have some information on an issue I am having with my 1973 Piper Challenger O-360 engine. I have about 900 hours on a remanufactured engine. I also recently installed a JPI EDM 830 engine monitor which is great by the way, but I recently have been experiencing some high CHT's on cylinders #1 & #4. I would like to keep my CHT's under 400 but actually these cylinders are not. They run 30-50 degree hotter than the rest & even hit 450 (Red Alert) at different times. Below are my scenarios: Cylinder #1: This cylinder will run hotter in cruise for some reason after I have leaned ROP, (around 9.5 GPH), using the EDM 830. It runs hotter continuously 30-50 degrees until I enrichen the mixture to around 10.5 - 11.0 GPH. Cylinder #4: #4 runs hotter at take-off 30-50 degrees even up to the Red Alert of 450. I think it got up to 454 degrees before I was able to lower the nose to increase airspeed during the climb to cool it off below the Alert Speed of 450. Here is a link to Savvy Aviation showing 62 of my flights & most recently the one I want to draw attention to is 10/15/22, Perryville, MO (K02), to Salem, MO (K33), that shows this phenomenon of high CHT's. 


Here is more detail of the issue I was experiencing on this particular flight.  During my recent trip to our Missouri farm, here is a fuel stop leg I took from Perryville, MO to Salem, MO and as I was taking off with full power & full mixture rich, I then got an EDM 830 alert at about 2000 feet that my cylinder #4 was blinking RED & was over 450 degrees, (454 to be exact), so I immediately lowered the nose & turned back towards the airport thinking I could be having a serious problem. However, once I lowered the nose & pickup'd airspeed, the CHT on #4 started to lower back into a more normal range so I decided to continue my trip which ended up as a non-event. Then on the other 2 legs back to Ohio, I noticed the same thing happening, but I lowered the nose, increased airspeed, just before it got to the Red-Line of 450 degrees. So, I am wondering if I have an engine problem especially that now I have 2 cylinders running extra hot! Any idea what I might do, or should I be worried? Thanks in advance for any input. Don


  • Hi Don,

    thanks for the post, and for showing us your data. Two questions for you, before I give you my guess about what is going on.

    1. Have you determined (by calibration) that your monitor is giving you accurate absolute numbers? Notice on nearly every flight your #1 is sixty degrees hotter than your #2, and maintains this difference, amazingly to within a degree or two, regardless of whether you're at full throttle or somewhere significantly less. That doesn't sound like an engine problem. Just for reference, when I checked the sensor-to-sensor match on my monitor a few years ago it was off something like 65-70 degrees from one to another.
    2. What did Saavy tell you when they reviewed your data?



  • Hi Bob,

    Thanks for the note, I haven’t heard from Savvy yet. No I haven’t checked on the calibration of the EDM. I assumed it was correct. How do you do that? On a positive note, the engine purrs like a kitten! I do have an annual coming up a little after the 1st of the year. So hoping to get everything checked out then but wanted to see if anyone had any ideas. Thanks again.

  • I would highly recommend at high and low powers leaning back slowly and noting when the EGT's peak on each cylinder. I suspect at least #4 is running lean and there is not much you can do about it if carb. Your can also try and repeat with a bit of carb heat.

    Aft cylinder baffling is almost always an issue as usually the baffle is tight to the cylinder - but if you look there is no air flow possible over a section as the fins are filled in that area. A slight gap with some baffling material can provide flow.

    The other challenge is retrofit systems that keep the primary gauge often use a different type or sensor that can read high or low for that cylinder.

    Reviewing the data:

    Cylinder 4: Highest EGT and CHT on take off power. Suggest it is running lean.

    Cylinder 1: Lowest EGT on takeoff suggest it is running rich OR very lean. Modest CHT's at takeoff power suggest rich vs lean. In cruise the CHT's are near peak despite flowing ~ 65% power level. These temps should not be possible at cruise at this power setting. The confounding dataset is the EGT which is very stable and in population. It as if runs very rich on takeoff and then there is a cooling issue blocking flow only in cruise.

    I would swap CHT's and see if the problem follows the sensor. It does not seem inherently a sensor issue as they track nicely post flight.

    Here is an interesting Lycoming graph to ponder. You may note the steep curve in CHT on the lean aside. Could the other three cylinders be lean vs the #1 that is at peak temp? You only know the total fuel flowing - not which cylinder.

    Eric Panning
    1981 Seneca III
    Hillsboro, OR (KHIO)

  • Hi Don,

    You just gave us the most important clue of all: if your baby is running smoothly, then all cylinders are making the same amount of power to within a percent or two. And if that's the case, then all intakes must be seeing a nearly identical charge. Beating the dead horse a little more, and referring to Eric's plot, if you assume a real absolute sixty degree CHT delta (and convert to Celcius, thanks Eric... : - ) the cylinder-to-cylinder power difference would likely shake your engine off its mounts.

    The first time I did a calibration I used the Manhattan project approach, and borrowed a lab oven. Since then, I've had good results with a Southern Labware hotplate. Mount the hotplate in the center of your engine, put all the sensors on the hotplate weighed down by a good thermal conductor like a block of aluminum, and sweep the temperature setting while recording the readout on your monitor. You will probably see a nearly constant difference between the sensors throughout the operating temperature range.


  • Eric & Bob, thank you for your responses. You have given me at least a place to start with my maintenance shop. Thanks again for your replies. You both seem very knowledgeable.


  • Don, adding to Bob's comments. Those sensors rarely have any significant delta by design. The temp deltas I have seen are almost always based on where they are located.

    For example, if your gauges are not primary then your original system must remain. If CHT measures from the #1 cylinder then the JPI system must use a spark plug hole "ring" to read CHT #1. This would definitely read higher than the stock location. You can see this easily by inspecting the spark plugs and if #1 has a an addition thin wire (top or bottom plug) that is your sensor wire. I would talk to your monitor supplier if you can take that into account in calibration.

    They also make doubler connectors so two sensors can use the same CHT probe hole. Talk to your mechanic about this path.

    While we are on the topic. Erratic readings in CHT are not physically possible. If you have a CHT sensor jumping around by 100's of degrees over seconds it is definitely sensor and not engine. A possible cause for something like this is it drops out of the cylinder hole and it close to the exhaust. That is not the case for your plane from the data but it is a possibility to consider for others.

    Eric Panning
    1981 Seneca III
    Hillsboro, OR (KHIO)

  • You might want to have your A&P verify that none of the sensor wires (EGT, CHT) have been spliced and extended. It is possible to do so but requires the same type of thermocouple wire. Normal copper wire can produce inaccurate readings.


  • edited November 2022

    So since you mentioned these temps were "recently", were they normal before and right after the scanner install?


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

  • I don't want to distract from this conversation but I did want to link to another recent discussion on this topic, just fyi:


    Digital Product Manager
    Piper Owner Society

  • We had a consistently high CHT3 reading on our O-360 engine. We checked baffles and the metal dams between cylinders (can be installed wrong) and found no issues. In frustration, we decided to replace the probe with a new one from the factory. The temp on CHT3 went back to the normal range. We looked at the removed probe and it had a bright ring like appearance on the top flat end of the probe suggesting that I was contacting the top end of the cavity that it screws into. This might have provided a more direct heat path to the probe than if it were not touching anywhere except at the screw in base. Anyway, probes can be an issue. Since you have two "hot" cylinders, it sounds more like a cooling issue (leaky baffling etc.) or mixture distribution issue. If you have a normally aspirated engine (carburetor) try adding some carb heat while you adjust for LOP. The carb heat causes some turbulence in the flow to the carb and it is theorized that this helps make the mixture flowing to the cylinders to be more uniform. It works for us. Mike Busch has some good articles on how to run LOP and ROP and also articles on the theory of engine combustion and how to avoid detonation. Also we have had problems at the couplings where the probe wire connects to the thermocouple wiring leading back to the engine analyzer. If your cylinders are instrumented then there will be dozens of these couplings and vibrations can cause loose connections that show up in the data as jumpy lines or values dropping to zero. We've had to locate and re tighten these couplings on several occasions making them a weak link in terms of reliability.


  • Thanks all for your comments…I really appreciate them. I’m scheduled for maintenance after the 1st of the year & this issue will be one of my top priorities to try & figure out. Thanks again.

  • Don,

    Our club has a O-360-A3A on a 1964 Cherokee 180. Here is a mistake we made dealing with high CHTs, much as you described, consistently topping 450F in climbs and even in cruise on hot days. First check your probes and instrumentation! It's relatively fast and cheap. We did the reverse unfortunately, including... Savvy aviation analysis, baffling checks, engine timing, induction leak checks, Fuel flow checks, sending it back to overhaul shop. It was there that they told us their gear indicated lower CHT temps by up to 30F from what we were indicating on our engine monitor. Instead of trying to ship the engine monitor itself back to JPI, we swapped probe tips and later bought a new set of probe needles. Now we are consistently operating in high 300s F and peaking out in the 420/430s instead of sounding the 450F alarms. I personally came to the conclusion that these engines had cooling designs developed back in the 1940s and 1950s without instrumentation and CAD tools available today, and that Lycoming says 500F is max CHT anyway. So.... start with the easy stuff, new probes and their positions. I don't sweat it anymore. Good luck.

  • Good advice…thanks.

  • Well here is an update on my high CHT’s I described earlier. My Cherokee Challenger 180 went into it’s annual this past month including the high CHT’s on #1 & #4 cylinders on my O-360-A4M engine at 900 hours. :-( The shop looked at every angle including testing probes, baffles, & borescoping cylinders. All cylinders looked good. Only thing found was a lot of carbon on top of #1 & #4 cylinders. This is supposedly due to me running extra rich to keep the cylinders cooler during flight operations. We even had good compressions, all in the 78-80 range, In draining the oil they noticed a silver aluminum sheen in the oil. In further examining the oil, by screening it through a coffee filter, they found some metal & aluminum particles. They cut open the oil filter & found a few particles there as well. Then they sent an oil sample to a lab for additional analysis & they confirmed but said lot of the metal was from regular wear & tear but said further examination of the engine was in order. Then the engine tear down began finding scars on piston wrist pins & the cam shaft. So 2 different IA’s declared an overhaul was warranted to make my Cherokee airworthy again. :-( So after getting 3 proposals from engine overhaul places, we made the decision to go with Columbia Aircraft Engine Overhaul in Pennsylvania with a 10 week lead time. Other lead times were 12 weeks & 24 weeks, respectively. So now we are waiting!

    While we are overhauling the engine, we have decided to add single electronic ignition on 1 Mag for more horsepower & fuel efficiency. I hear that double electronic ignition systems are now available with a battery backup from SmoothPower, so I am going to check on that. Are there any other considerations I should be considering while we have every thing torn apart?



  • Hi Don,

    Glad to hear you're moving forward on the project!

    Can you post the lab report for your oil analysis?


  • Bob,

    Sorry it’s taken me a few days to post my oil analysis for your view. The oil analysis was not the smoking gun for the overhaul but it did point us to look further. After we tore into the engine, we found the cam shaft & tappers not up to par, thus the overhaul. Here attached is the oil analysis….

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