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Thread: Engine Temps

  1. #1

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    Engine Temps

    Greetings forum! I recently purchased a Super Cub. Narrow deck 150 Lycoming 0320. Flying it on the east coast below about 3,000 feet. CHT runs about 400 to 410 degrees at 2350 to 2400 rpm. I note the lycoming manual indicates absolute red line of 500 degrees and typical high cruise power at 410-430, though I've read a few opinion pieces about keeping CHT between 365 to 390. So, am wondering if I should be concerned with typical CHT at 400-410 during cruise at 2400rpm outside air temp approx 85 degrees. Thanks,

  2. #2
    Steve Pierce's Avatar
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    I would google this string of words. You will find a lot of information. Key is airflow.

    high cht site:supercub.org
    Steve Pierce

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  3. #3
    behindpropellers's Avatar
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    What are you measing CHT with? What cyl?

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    Probe on back left (#2cylinder)


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    Yes the temp is too high. Google as Steve instructed and then get a proper 4 cylinder cut/egt.
    DENNY

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    WindOnHisNose's Avatar
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    May want to check your e-gap and engine timing.

    Randy
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    Eddie Foy's Avatar
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    Back, left is #4
    Eddie Foy
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    Christina Young's Avatar
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    This question has been discussed to death on this site without consensus... I have the same issue and don't know whether to be concerned or not. In fact, I am willing to bet that MOST of the super cubs out there run this hot!

    Flying up to and around Alaska this summer I have made it a point to ask every cub owner and pilot what CHTs they run. Here is a sampling of the responses and observations:

    - From Lycoming factory rep at a flyin in PA: 400 to 430 in cruise is ok - our engineers set those numbers for a reason, they are in the manual.
    - From a well known A&P/IA on this site I visited on the way up: I cruise at up to 450 in my 150HP cub without any issues all the time.
    - A commercial operator with a 160 HP in a remote part of Alaska: we are seeing CHTs up to 480 in climb, and we have to take corrective action to bring it down. We cruise at over 430 all the time.
    - From a well known supercub.org member up here: read the Lycoming manual... they are right. And rip that damn CHT gauge out and stop worrying!
    - From a well known bush pilot for something like 40 years up here: I don't have any CHT gauges in any of my aircraft. Oil temp is what's important! Look at all those Florida banner tow pilots that don't run any cowling at all!

    MOST of the cubs here in Alaska don't have any CHT gauges and have no idea what temps they're running... and also don't seem to appreciate the airflow issues that Steve refers to! Many have wide open bottom cowls where the air filters and starter holes are.

    But I can't help worrying that running this hot will not cause some damage, and have been taking all the recommended steps to bring mine down (so far without success). My manometer readings have been between 5.5 - 6 inches as recommended by Lycoming... that's with a slow 160 HP cub with 31" bushwheels, etc.

    Just some observations.... wish I knew the answer, especially when flying in some of these really remote areas...
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    Christina,my theory is a good 60 percent of cubs have analogue gauges out there are on one cylinder and are at least 50 years old.On top of this most have probably never been tested or overhauled.What I am getting at is that we were quite happy with that single engine cht reading.Now we have multi cylinder readings and digital gauges and we are finding out the cht's are quite different from one another and frequently higher or lower depending on angle of attack,power and speed.I think the best thing we can do is put an old gauge back in and put the thermocouple on the number 1 or two cylinder and relax and enjoy flying,the engine will still probably reach TBO and we won't have ulcers.
    Quote Originally Posted by Christina Young View Post
    This question has been discussed to death on this site without consensus... I have the same issue and don't know whether to be concerned or not. In fact, I am willing to bet that MOST of the super cubs out there run this hot!

    Flying up to and around Alaska this summer I have made it a point to ask every cub owner and pilot what CHTs they run. Here is a sampling of the responses and observations:

    - From Lycoming factory rep at a flyin in PA: 400 to 430 in cruise is ok - our engineers set those numbers for a reason, they are in the manual.
    - From a well known A&P/IA on this site I visited on the way up: I cruise at up to 450 in my 150HP cub without any issues all the time.
    - A commercial operator with a 160 HP in a remote part of Alaska: we are seeing CHTs up to 480 in climb, and we have to take corrective action to bring it down. We cruise at over 430 all the time.
    - From a well known supercub.org member up here: read the Lycoming manual... they are right. And rip that damn CHT gauge out and stop worrying!
    - From a well known bush pilot for something like 40 years up here: I don't have any CHT gauges in any of my aircraft. Oil temp is what's important! Look at all those Florida banner tow pilots that don't run any cowling at all!

    MOST of the cubs here in Alaska don't have any CHT gauges and have no idea what temps they're running... and also don't seem to appreciate the airflow issues that Steve refers to! Many have wide open bottom cowls where the air filters and starter holes are.

    But I can't help worrying that running this hot will not cause some damage, and have been taking all the recommended steps to bring mine down (so far without success). My manometer readings have been between 5.5 - 6 inches as recommended by Lycoming... that's with a slow 160 HP cub with 31" bushwheels, etc.

    Just some observations.... wish I knew the answer, especially when flying in some of these really remote areas...
    Just finished building a back country cub
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  10. #10
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    Back in 1990, I bought my cub with a Westach CHT/EGT gage in it with 500 hrs on a new engine. After a few trips across Wyoming in the summer,(E to W) I was five cylinders poorer. I then launched an investigation as to why. My gage had a resistance of 25 ohms, which lugged down the thermocouple voltage about 30 per cent.(it still read more or less correctly) I inserted an Analog Devices AD594 chip,(which does not lug down the thermocouple voltage, and it corrects for the cabin temp) and calibrated the probe with a can of oil, a torch, and several candy thermometers. I found out that my 'figure of merit' was 390. 390 + OAT= CHT....So, I was at 480 CHT at 90F OAT....a few(well, lots of) changes to the cowl brought it (the figure of merit) down to 310. Dropping in a Niagra "cub cooler" took care of the oil temps.
    Last edited by fobjob; 08-10-2017 at 09:36 AM.
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    Many thanks to all who contributed to this discussion. Definitely wiser on the issue of CHTs! My take-away from this and other discussions and research is that my CHT for a 150hp narrow deck Lycoming at around 400 in cruise at 2400 RPM is within factory tolerance and is "normal". Ideally, though, they can be lower and some work to ensure proper baffling and air flow will be helpful. Fly Safe, Spad

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    I spent 6 hours flying in the mountains on Sunday. Depending on altitude, outside temp, and RPM setting. I observed three different cylinders have the highest CHT. Number 2 can be hotter than 3 or 4 depending on conditions. I asked the Lycoming rep at the trade show I they ran the cylinders at a CHT of 500 degrees for 2,000 hours. His reply was it was a much shorter test time and they cycled the temp up and down. Without proper instruments you don't know what you don't know.
    DENNY
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  13. #13

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    Quote Originally Posted by Spad View Post
    Many thanks to all who contributed to this discussion. Definitely wiser on the issue of CHTs! My take-away from this and other discussions and research is that my CHT for a 150hp narrow deck Lycoming at around 400 in cruise at 2400 RPM is within factory tolerance and is "normal". Ideally, though, they can be lower and some work to ensure proper baffling and air flow will be helpful. Fly Safe, Spad

    I've learned (reciently) just how much temps depend on which prop you're spinning, at what altitude and how aggressive you lean it which seeing an increase in oil temp will be a tell tale warning sign of if you have an accurate digital gauge to watch it on.

    Remember, the stock props take a bunch of manifold pressure to swing down low at 2400 and that makes heat and the Borer spins much easier so even though we may be turning it much faster the MP is lower therefore the power (temp) required to turn it is much less.
    Last edited by OLDCROWE; 08-10-2017 at 01:43 PM.
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  14. #14

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    Quote Originally Posted by Spad View Post
    Many thanks to all who contributed to this discussion. Definitely wiser on the issue of CHTs! My take-away from this and other discussions and research is that my CHT for a 150hp narrow deck Lycoming at around 400 in cruise at 2400 RPM is within factory tolerance and is "normal". Ideally, though, they can be lower and some work to ensure proper baffling and air flow will be helpful. Fly Safe, Spad


    400 in cruise is too hot and by no means "normal"
    especially on a front cylinder unmodified
    150.
    I bet your instrument is off
    check your gauge for accuracy then install probe on #3 cal and see where you are

  15. #15

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    400* is the common threshold for "normal" temps in my circle of friends. 399 is good. At 401? I find a way to get it under 400.

    What kind of temp probe?

  16. #16
    mvivion's Avatar
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    Quote Originally Posted by stewartb View Post
    400* is the common threshold for "normal" temps in my circle of friends. 399 is good. At 401? I find a way to get it under 400.
    Same here. If I were flying a Super Cub with CHTs over 400, I'd figure out if it was really that hot, and fix it if it was. I've flown probably a dozen Super Cubs a lot, and many others for a brief time, and only had that sort of temps once, and that engine was poorly installed.

    MTV
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    Ok, so #2 is at 400* at 2400 and "normal", we all seem to be in agreement that anything over 400 is reason for concern.
    What happens when you add a little power or start to climb? 435*+?
    My money is on erroneous instrument reading. otherwise youre running too hot and have some work to do.
    Last edited by Oliver; 08-10-2017 at 11:28 PM.

  18. #18
    PerryB's Avatar
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    I've seen a lot of installations with rather poorly fitted boxes/baffles and very generous widths of silicone sheeting that kinda just flopped all over like lasagna noodles. Of course the idea is that they blow into place and seal everything up in flight, but I have considerable doubts. The nose bowl is another big place for leaks, and I've seen some pretty optimistic use of silicone strips up there as well. I have a fairly well fitted box with the 1/2" felt edging, and that seals against 1/2" low density foam weatherstripping inside the top sheet. The nose bowl felt is snugly contoured and I've sealed around the oil cooler with foam pipe insulation. As a result it runs very cool. Its a 150/320 with a Catto 82-39 or a Mac 82-42 (no difference in temps) and I've never seen 400 under any circumstances. Cruising at 2400-2450 and 92-93 mph, I'll see about 350-360 deg. (EI digital- #4) at the previously mentioned 85 OAT. This is near sea level FWIW. Oil typically runs ambient plus 105-110 with a Niagara aluminum cooler. I'm convinced baffling / sealing is most of the battle. My $.02
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  19. #19

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    Quote Originally Posted by Oliver View Post
    Ok, so #2 is at 400* at 2400 and "normal", we all seem to be in agreement that anything over 400 is reason for concern.
    What happens when you add a little power or start to climb? 435*+?
    My money is on erroneous instrument reading. otherwise youre running too hot and have some work to do.
    Thanks. Measurement is coming from back left, cylinder, #4, so hopefully that is warmest cylinder. Thanks for taking the time to respond.


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  20. #20

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    Quote Originally Posted by PerryB View Post
    I've seen a lot of installations with rather poorly fitted boxes/baffles and very generous widths of silicone sheeting that kinda just flopped all over like lasagna noodles. Of course the idea is that they blow into place and seal everything up in flight, but I have considerable doubts. The nose bowl is another big place for leaks, and I've seen some pretty optimistic use of silicone strips up there as well. I have a fairly well fitted box with the 1/2" felt edging, and that seals against 1/2" low density foam weatherstripping inside the top sheet. The nose bowl felt is snugly contoured and I've sealed around the oil cooler with foam pipe insulation. As a result it runs very cool. Its a 150/320 with a Catto 82-39 or a Mac 82-42 (no difference in temps) and I've never seen 400 under any circumstances. Cruising at 2400-2450 and 92-93 mph, I'll see about 350-360 deg. (EI digital- #4) at the previously mentioned 85 OAT. This is near sea level FWIW. Oil typically runs ambient plus 105-110 with a Niagara aluminum cooler. I'm convinced baffling / sealing is most of the battle. My $.02
    Thanks for head's up around the nose bowl and oil cooler. Am looking for some material to block some of that leakage. Thanks!


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