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High oil pressure 454 mercruiser

Discussion in 'Carver Yacht' started by Stardust, Jul 8, 2009.

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  1. Stardust, Jul 8, 2009
    #1
    Stardust

    Stardust New Member

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    I bought my 42 Carver last year. It saw a new short block (454 Gas Mercruiser)on the starboard side just before my purchase. The port oil pressure runs at 40psi. The star. shows ~80 cold and ~65-70 at oper. temp.

    Question:
    I am seeing a fair amount of leakage in the bilge. Could this be the high pressure forcing oil past the rear seal (assuming the oil guage is accurate)?
    Is there a way to adjust the pressure?
  2. Capt J, Jul 8, 2009
    #2
    Capt J

    Capt J Senior Member

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    There is no way to adjust the oil pressure on a 454. Have you put a mechanical gauge on the motor just to verify pressure? The oil pump is mechanically driven, located inside the oil pan, and it has a high pressure relief valve that I've seen in rare cases be defective and stuck shut. BUT in order to change the oil pump, you need to drop the oil pan, and that's probably a major job in your boat.
  3. wingless, Dec 20, 2009
    #3
    wingless

    wingless Member

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    Try transposing the wiring to see if it electrical.

    Also, the suggestion for a mechanical gauge is good, I've done that and it is a good sanity check that helped me find an electrical problem.
  4. Brooke's Buddy, Dec 24, 2009
    #4
    Brooke's Buddy

    Brooke's Buddy New Member

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    The front and rear seals only see oil splash,the crank and cam bearing clearance holds the pressure formed by the oil pump. Possible the rear seal is the wrong rotation,it's marked yellow for right hand. It may just be a high volume oil pump, also check that the remote oil filter hoses are not reversed,that would blow apart the paper pleats in the filter and plug up something. Any results on the mechanical gauge reading??
  5. Captrko, Sep 20, 2012
    #5
    Captrko

    Captrko New Member

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    I had the same problem on my Carver 42 (4207 Aft Cabin)

    I went and borrowed a oil pressure kit and checked it right at the engine, she was indicating 80 PSI upon start up and even after shutdown, but with the kit it showed 50 PSI. The oil pressure sending unit was bad (common issue on Merc 454's....
  6. Bill P, Sep 20, 2012
    #6
    Bill P

    Bill P New Member

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    If the oil pressure is indeed too high, you can adjust it by changing the tension of the spring on the by-pass valve on the oil pump.
  7. Capt J, Sep 21, 2012
    #7
    Capt J

    Capt J Senior Member

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    A stuck by-pass valve will cause excessive oil pressure, or a spun cam or main bearing sometimes also. You have to drop the oil pan to access the oil pump and bypass valve/spring on it.
  8. Capt Ralph, Sep 21, 2012
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    There is a gap and lip between the bearing and rear seal. You can not blow oil out this seal from high oil pressure.
    When I rebuilt LBCs, I used Melling 77 HV oil pumps. Most rebuild shops do. The pressure may be higher on a fresh block (closer tolerances) and your readings could be correct. Yep, Up there high.

    Put an old fashioned mechanical gage on both of the motors, You may see something totally different than what the electric gages say. Full page of reasons for this.

    On the oil leak;
    I have found truck & auto blocks used as replacement engines. Done rite (rarely) it's O K. Look for were oil dip stick tubes are located. Some LBCs go into the pan, some into the block. When there is a mis match, a lot of perm-a-tex is used and usually fails.
    Marine blocks use brass freeze plug, including the cap at the end of the cam shaft. I have seen the steel cap (plug) rusted and leaking oil from the back cam bearing (not open or lipped). Also, the distributor gasket can make a heck of a mess. Depending on where your H/E is, You may not even see this.

    Good luck, tell us what you find.