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  1. #1

    Default 4.3 liter mercruiser- no oil pressure showing at gauge

    Just changed oil in my 1999 4.3 liter mercruiser with Mobile 1 10-30 synthetic and a K&N oil filter. Showed good oil pressure when I warmed up the engine before the oil change and now that I have new oil and filter on and started the engine for initial warmup period it show's no oil pressure at the gauge. Engine sounds fine and oil level is up. Not sure if there may be goop in the sending unit or ?????????. Changed oil in a lot of engines and never had one not return oil pressure to the gauge. Scratching my head. Any ideas?

  2. #2
    Moderator Bondo's Avatar
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    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    Ayuh,... Welcome Aboard,... probably be coincidence...

    Ground the sensor wire,+ see if the gauge pegs,...
    Plumb in a mechanical gauge,...
    Any Grease is Better,..... Than No Grease at All.......

  3. #3
    Rear Admiral 180shabah's Avatar
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    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    verify with mechanical gauge before you do anything, don't want to risk the engine.

  4. #4

    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    Plumbed in mechanical gauge. No pressure. Coincidence that my oil pump takes a dump between an oil change??? Strange. Also tried grounding the wire to the electric gauge and it does not seem to max peg. I suppose this 4.3 has the mechanical oil pump located inside the pan! Just my luck.

  5. #5
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    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    Quote Originally Posted by Loaded Bullet View Post
    Plumbed in mechanical gauge. No pressure. Coincidence that my oil pump takes a dump between an oil change??? Strange. Also tried grounding the wire to the electric gauge and it does not seem to max peg. I suppose this 4.3 has the mechanical oil pump located inside the pan! Just my luck.
    if you have no pressure the valve lifters should be clacking away.

  6. #6
    Rear Admiral 180shabah's Avatar
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    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    zero oil pressure = pullin' the engine. pretty common for the pickup tube to drop into the pan.

  7. #7

    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    Crazy luck. I actually tried 3 different mechanical gauges and got no pressure from any of them but I noticed nice clean oil on the tip of the threaded part of the gauge when I pulled them out, so I figured I would turn the engine over to see if I actually had any oil at that point, when I did it there was some oil but not a lot until I pulled the cap off of the filler tube. I reinstalled the mechanical gauge and sure enough I have pressure again. Put the sending unit back on and my dash gauge is back to normal also. All I can figure is that by using the siphon type oil change through the dipsitck tube that I created an air lock in the system somewhere. Wow! sure glad I don't need to pull the engine! Thanks for you input and ideas. Sometimes it's good to walk away from the problem for awhile and talk to somebody rather than beating yourself up over it and overthinking. Ice is off the lakes, I'm goin' boatin!!

  8. #8
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    All I can figure is that by using the siphon type oil change through the dipsitck tube that I created an air lock in the system somewhere.
    That shouldn't be possible.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
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  9. #9
    Moderator achris's Avatar
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    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    Quote Originally Posted by Loaded Bullet View Post
    .... All I can figure is that by using the siphon type oil change through the dipsitck tube that I created an air lock in the system somewhere. ....
    Nope... Crankcase is externally vented... Can't pull a vacuum inside (or anything close to that)... This DOES NOT make sense.

    Maybe a bit of crud in the sender hole that got blown out when you ran the engine with nothing in the hole?

    Glad you're all fixed.

    Chris.........
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
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  10. #10
    Moderator achris's Avatar
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    Default Re: 4.3 liter mercruiser- no oil pressure showing at gauge

    Quote Originally Posted by don s View Post
    that shouldn't be possible.
    Snap!!!
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
    **
    Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
    **
    Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

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