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What is ''normal'' DD 71 series oil pressure?

Discussion in 'Technical Discussion' started by cleanslate, Jun 4, 2019.

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  1. cleanslate

    cleanslate Senior Member

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    Hello,

    I'm wondering what my YF friends DD 71 series engines , on average,are reading on their oil pressure gauges at running temp, 180 F. at idle, 700 rpm, after a day's run? Mine are low usually under 10psi , maybe 5psi.
    My port engine this weekend, got real low at idle...near 0...but came back up with added throttle.
    I have to put a mechanical gauge on the engine directly this weekend to get a real reading. I'm not sure if something is a miss with the electrical one on the helm dash. Or I have new issues...yay!

    I was trying to find an older post on this, thought I read one a while back, but had no luck.
  2. boatme99

    boatme99 Member

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    I ran 1978 model 1271N's, they were specd at 50 - 70. Low - 30, dropping lower with wear.

    Did the needle bounce when the pressure dropped or just get low and stay there?
  3. Capt Ralph

    Capt Ralph Senior Member

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    Hot oil in a 71 (53, 92,149) can read below 5psi at low idle. Don't get bent.
    Sadly, oil flow is measured in this crude PSI measure. If the sump is up, It's flowing.
    My stock 5PSI alarms sometimes go off when clutching the engines. All is good.

    50-70 PSI is at higher rpm and under load.
  4. Capt J

    Capt J Senior Member

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    This is my experience with most 12 cylinder 71's. Even after majors. I've seen a lot of them after running at cruise, hit the 5 psi alarm when clutching them in and out of gear, waiting for a bridge or something. 8v71's seemed to make more PSI and were around 10-20 psi at dead idle in the same situation for some reason.
  5. cleanslate

    cleanslate Senior Member

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    Thanks Capts for the replies...mine 471TI's . Any way I know they are low at idle. But I feel my port engine is up to something, it's low. Had an Anchor out BBQ ribs party with friends last Saturday into the night. Was not in the mood to go into the engine room/bilge on Sunday to pull the oil stick and check it for fuel in the oil or what ever. Going to face my Detroit music this Friday.
    Had a leaking injector tube last year which caused low pressure of course. Hopefully it's not happening again, or on the other hand that's an easy fix to the alternative possibilities. Both engines read around 25/35 PSI at 1550 or higher RPM under load. I do know they are getting tired. hours un-known. But they keep on running and that's fine with me.
    Just picked up an oil pressure test kit from the automotive store so I can get the real pressure reading.

    Not even sure if the low oil pressure alarms work? They only sound when I start the engines. How do I test those? They are J & T's
  6. PacBlue

    PacBlue Senior Member

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    Here's a Lube Oil Section for a DD 4-71TI rated 325bhp @ 2600rpm:

    upload_2019-6-5_14-12-51.png
  7. Capt Ralph

    Capt Ralph Senior Member

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    When you start the engines, fuel pressure comes up first. A fuel pressure switch around your secondary fuel filter, enables the oil pressure alarms. You only hear the alarm for a second or so.
  8. cleanslate

    cleanslate Senior Member

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    Thank you for this info. You always amaze me with the info you can dig up. Mine I've been told are the 285 hp rating ...who knows? When I'm at J & T next time I'll give the my engine numbers and see what HP they tell me. Any way mine top out at 2350 rpm. But they never see that with me! I don't push old engines. I cruise at 1550 rpm and at times 2000 rpm.
  9. cleanslate

    cleanslate Senior Member

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    Ok got it. But mine have not gone off when my port engine got low last week. How do I know they really work? Other than the initial start up. Is that the only test?
  10. boatme99

    boatme99 Member

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    Also, have you checked your oil sending units?
    At about $20 each, they're cheap insurance.
    Over 14 years on 1 boat with 1271s, I had to replace the SB unit 3 times. Never had to replace the port unit.

    Does your water temp. rise? If the ngine is starving for oil, the temp will rise pretty quickly. It may just go up slightly at first. You have to know where your guages read all the time so you can notice any slight changes.
  11. wdrzal

    wdrzal Senior Member

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    Wonder if the 28 gal/min stated is @ 5 psi and @ 42/55 psi ????
  12. PacBlue

    PacBlue Senior Member

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    The 28gpm would be at the rated speed (42-55psi). The flow rate would vary by rpm, don't know what the output is at low idle (5psi).
  13. Capt Ralph

    Capt Ralph Senior Member

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    Find the fuel switch, jump the two wires on it (key switch may need to be on but engine not running), low oil alarm should sound.
  14. cleanslate

    cleanslate Senior Member

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    Ok , Mr.know-it-all-here...Lol
    Not sure where or which one is the oil sending unit on my engine...lol.
    I see two , one coming off the twin disc trans and another one with two lines coming off of it near the trans upper middle rear of engine...
    I think that's it?
    One single one on top of the engine center, must be the water temp sender ?
  15. Capt Ralph

    Capt Ralph Senior Member

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    another one with two lines coming off of it near the trans upper middle rear of engine..

    define lines? Tubes or hoses or wires?

    Anything hidden by the exhaust manifold or starter on the block sides?

    Re your secondary fuel filter, is there a sender around it? or a small tube/hose going to a block and one or two senders on this?

    J/T luvs to hang lots of gizmos (Junk&Trash) on their engines.
  16. boatme99

    boatme99 Member

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    The oil pressure sending unit is electrical.
    On DD, it's about 1 1/2" diameter, screws into block, has a single threaded post with nut to attatch wire.
    I'm not sure but I think newer engines could use a different 2 wire unit.

    Dang, can't load a picture!

    It's located on the right side of the block. It simply screws into the block and the wire attatches to the other end. Believe me, when you see one, you can't get anything wrong! It's very basic. Screw in - attatch wire.

    Only thing to remember! Never use Teflon tape or thread sealer! The unit threads must contact the block. One wire, remember?

    Looking at other responses though, I don't believe the sending unit is a problem but you should keep one on board for a spare.
  17. cleanslate

    cleanslate Senior Member

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    image.jpg
  18. cleanslate

    cleanslate Senior Member

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    Is this it?
  19. boatme99

    boatme99 Member

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    Yep!
    Jeeze, they didn't give you much room!
  20. Capt Ralph

    Capt Ralph Senior Member

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    Yep, little one for the alarm, big one for a gauge.

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