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Thread: Operating temp, pressure, and CHT

  1. #1
    Member krwsr's Avatar
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    Operating temp, pressure, and CHT

    Where does one find the recommended operating temps {oil & CHT} and oil pressure for the 4A084-4?? I have not been able to locate it anywhere in the manual.
    Project "Swamp Fox"
    Hull: 12' x 6' x 18" All welded aluminum
    Motor: 4A084-4 Continental NOS / Solex 34 Carb
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    Prop: 57" Ultra-Prop

  2. #2
    Member krwsr's Avatar
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    Re: Operating temp, pressure, and CHT

    I was able to find this info from homebuilt .com.

    PAGE 31

    1. Re: Help! teledyne 4A084 Military

    I have found this document,which describes the result of testing some military general purpose engines (including the 4A084) with different low lead and unleaded fuels.

    Around PDF page 31 or so you will find the results of the 4A084 tests, including the measured temperatures and oil pressures. Note that these are what they measured, not the allowed values.

    From what I see, the CHT is from about 325 to 510 degrees F. EGT is around 1000 to 1200 degrees. Oil temp around 200 to 260 degrees. Oil pressure from about 30 to 50 psi.


    Project "Swamp Fox"
    Hull: 12' x 6' x 18" All welded aluminum
    Motor: 4A084-4 Continental NOS / Solex 34 Carb
    Direct Drive
    Prop: 57" Ultra-Prop

  3. #3
    Super Moderator Corky's Avatar
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    Re: Operating temp, pressure, and CHT

    Thanks for the research..I'm suprised nobody chimed in on what their 084 was running...I've read aerokirks magic number was 475* on the CHT...Not sure where that number came from...I do know excessive oil and head temps lead to accelerated wear and even a new engine is short-lived under those conditions... Note the #3 cylinder had the highest CHT and at the end the lowest compression...
    Last edited by Corky; 11-21-2014 at 09:26 PM.

  4. #4
    Administrator Papee's Avatar
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    Re: Operating temp, pressure, and CHT

    I think the mod on the intakes where I hog out the excessive webbing and the new carb setup will help the temps. I dont run CHTs just oil temp. Before the mods It would climb as far as 180+, I never left it get higher, I always slowed down until it cooled off before starting off again. I never shut it down just idled for a bit then hit it again. It didn't take long at all to cool back down, only a minute or two of idling. With the new carb and intake mods I can run it hard for a good amount of time without it running over 180. Most of the time it is 160.
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  5. #5
    Administrator Papee's Avatar
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    Re: Operating temp, pressure, and CHT

    Quote Originally Posted by krwsr View Post
    I was able to find this info from homebuilt .com.

    PAGE 31

    1. Re: Help! teledyne 4A084 Military

    I have found this document,which describes the result of testing some military general purpose engines (including the 4A084) with different low lead and unleaded fuels.

    Around PDF page 31 or so you will find the results of the 4A084 tests, including the measured temperatures and oil pressures. Note that these are what they measured, not the allowed values.

    From what I see, the CHT is from about 325 to 510 degrees F. EGT is around 1000 to 1200 degrees. Oil temp around 200 to 260 degrees. Oil pressure from about 30 to 50 psi.

    I didn't have time to look at it but
    Is the document mentioned here something I should save and include with the other 084 documents I have here?
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  6. #6
    Super Moderator Corky's Avatar
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    Re: Operating temp, pressure, and CHT

    The document is a test of 3 military engines{ the 084 being the biggest displacement} and the effects of leaded,low-lead and no-lead fuel on them...Other than the entertainment value of the tests there's really not anything that would pertain to us using the engines in our application...Oddly enough the no-lead had the least deposits and valve issues...One 084 lost a pin in the magneto unrelated to the gasoline...So the short answer would be no...Other than the info krswr extracted from the tests IMO I'm not seeing anything of value for the site...

  7. #7
    Member aerokirk's Avatar
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    Re: Operating temp, pressure, and CHT

    I've attached the document in which I found reference to the maximum CHT value of 475 deg F that I stated in my post. I'm pretty sure that this is a conservative value but I never let mine get beyond 500 deg before letting off.
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    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
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  8. #8
    Administrator Papee's Avatar
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    Re: Operating temp, pressure, and CHT

    I think it gets to a point that we are over cautious, If we had all the gauges on to monitor the engines we would need a 2'x4' dash. I've been running my boat since 2008 by just monitoring the oil temps. If any of the other things like CHT get higher they will also raise the oil temps, by keeping the oil temps in range and watching them will give your enough assurance that your engine is running fine. Now If I were in the air with this setup it would be a different story. As I mentioned, the intake mod helps with the rear cyl getting hotter a bunch by allowing more gas to get the both rear cyls.
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  9. #9
    Super Moderator Corky's Avatar
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    Re: Operating temp, pressure, and CHT

    Aerokirk thanks for posting the temperature limits...I did'nt know there was an installation instruction document...
    So if the intake design ran the two rear cylinders hotter that's probably a good place to run the CHT to monitor one of them ...I'm all for the oil temp gauge and probably the CHT gauge as well but the EGT gauge might be overkill for our application IMO...I wonder how well an infrared {no touch}point-and-shoot gun would work for some readings...

  10. #10
    Member aerokirk's Avatar
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    Re: Operating temp, pressure, and CHT

    Corky ... I agree that an EGT is probably not worth adding. In an aircraft they are vital, mostly because air density decreases with altitude and as an airplane climbs you have the ability to lean the mixture to keep the proper air/fuel ratio. You don't have a mixture control on the 084 so the CHT is of more value. I've checked my EGT readings by using an infrared gun and they're fairly accurate. You can sort of find the hottest cylinder with one but it could be misleading since the boat is not moving so you don't have the ambient airflow that you would at speed.

    I think that Papee has posted all the 084 documents on this site ... check the forum list.
    11'6" Marty Bray Hull
    4A084 Continental
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    67" Whirlwind Razor X Prop
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  11. #11
    Member aerokirk's Avatar
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    Re: Operating temp, pressure, and CHT

    Quote Originally Posted by Papee View Post
    I think it gets to a point that we are over cautious, If we had all the gauges on to monitor the engines we would need a 2'x4' dash. I've been running my boat since 2008 by just monitoring the oil temps. If any of the other things like CHT get higher they will also raise the oil temps, by keeping the oil temps in range and watching them will give your enough assurance that your engine is running fine. Now If I were in the air with this setup it would be a different story. As I mentioned, the intake mod helps with the rear cyl getting hotter a bunch by allowing more gas to get the both rear cyls.
    I generally agree Papee except that the CHT gives you more of a real time indication of over-temp than oil temperature. When you tromp on the gas the CHT will increase quite rapidly to a fairly high value and will remain there for several minutes before the oil temp reaches maximum. That being said, you've had more experience with the 084 than most of us and your engine has withstood the test of time so it shows how tough these engines are.
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
    SS Rigging

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