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  1. #1
    Join Date
    May 2011
    Location
    Lake Erie Ohio
    Boat
    Sea Ray
    Details
    1989 Sea Ray 340 DA
    Engine(s)
    twin 454 Mercs
    Posts
    4,127

    EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    Hey Everyone,

    Been busy for me lately but Aftica let me down for the first time of the season. Took her out fishing with 6 people more then normal and had to go over 3000rpms. Normally I never go higher then 2800rpms and I cruise at 25,26000 rpms. When I got above 3 grand my oil pressure drops to near nothing and bounces around 10lbs. I put a mechanical gauge on and I got the exact same readings. I am going to be tearing the back end out this weekend and pulling the port engine Monday. My hope is it is a cracked pickup tube. Anything else that I need to look for? I also plan to replace the oil pump while I have her out. This is the only thing I can think of why it would cause this. It is also not low on oil and I tried adding an extra 1/2 qt just to make sure its not going dry.

    Any other ideas, or does a cracked pick up tube seem likely?

    Thanks all...

  2. #2
    Join Date
    Jun 2011
    Location
    Puget Sound Wa
    Boat
    Sea Ray
    Details
    1999 Sundancer 270DA SE Foss Landing & Marina Tacoma,WA
    Engine(s)
    5.7L w/ Bravo II
    Posts
    983

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    You could pull one valve cover off and see if you have plenty oil flow on the top end if you do it's possible you have a bearing that has spun or is worn out either cam or main bearing will do this without any noise if it were a rod bearing there's usually noise. With luck it's just the pump.
    Bob & Sue
    Puget Sound Wa

  3. #3
    Join Date
    Dec 2006
    Location
    Washington DC
    Boat
    Sea Ray
    Details
    1994 370 Express Cruiser
    Engine(s)
    454 Mercruisers
    Posts
    839

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    I'm a little confused....does the oil pressure still read fine to 2800 rpms? Or does it read very low pressure now at all rpm ranges?

    -John
    RestorationMarine.com

    ASE Master Mechanic

    1994 -370 Express Cruiser
    Washington, D.C.

  4. #4
    Join Date
    Oct 2008
    Location
    Southern MD/ Potomac river
    Boat
    SeaRay
    Details
    1989 340 EC
    Engine(s)
    7.4LX2 Hurth 630A Drives 6.5Kw QS Genny
    Posts
    947

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    Be sure to check the pump drive system. Drive shaft and Distributor Gear. The shaft should be the slotted style and not the hex style, which are more prone to spinning. Are there any noises when the pressure drops, or anytime for that matter?
    Not sure how clean the engines are, but agree with Bob to check the oil drain back holes. It is possible that all the oil is pooling in the valve cover area and can't drain back fast enough. Usually this happens on a sludgy engine, and will cause leaks at the valve covers over time since they don't seal that well. Another sludge spot would be the pickup tube screen clogged up, can also be from other junk in there ( I have seen rebuilt engine with so many pieces of rag in the oil that 3/4 of the screen was blocked.
    That's about all I can think of other than a failing pump or bad news inside.

    1989 Sea Ray 340EC
    2X 454BB 6.5Kw QS Gen
    Hurth 630A straight drives

  5. #5
    Join Date
    May 2011
    Location
    Lake Erie Ohio
    Boat
    Sea Ray
    Details
    1989 Sea Ray 340 DA
    Engine(s)
    twin 454 Mercs
    Posts
    4,127

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    thanks all, she reads 50lbs under 3k. over 3k loose oil pressure. the engines are clean. we removed the covers and the internals are clean. the engine has roughly 650 hours and i change the oil religiously every 50 hours. also no sounds at all. no tapping or knocking. My mechanic was all over it looking for something that made sense and he's as upset as I am. we will pull it out and go over it until we find something... ill keep you posted.

  6. #6
    Join Date
    Dec 2006
    Location
    Washington DC
    Boat
    Sea Ray
    Details
    1994 370 Express Cruiser
    Engine(s)
    454 Mercruisers
    Posts
    839

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    Ok....before you pull the motor let me suggest something simple.

    What you have said:
    1) is that you never take your boat over 2800 rpms and everything is fine up to that point.
    2) On the one time you go over 3000 rpms the pressure drops to zero
    3) A mechanical gauge shows the same thing
    4) Oil pressure returns to normal below 3000 rpms.

    So you are dealing with a problem that most likely has been hidden from view for some time because you never went above 2800 rpms.

    There are only a few basic things that can cause what you are experiencing but the symptom is that the oil pan is going empty at 3000 rpms which is causing the drop in pressure.

    1) Broken oil pickup....separated from oil pump....basically runs out of oil
    2) Broken oil pump pressure spring (unlikely because pressure would not be 50 pounds)
    3) Bad oil pump drive mechanism (unlikely because it would get worse and eventually start losing pressure below 3000)
    4) Bad bypass on the oil filter (what kind of oil filters do you use?)

    Some oil filters use bypasses which open if the filter experiences too much pressure from the oil pump. If it opens...pressure drops. Put a mercruiser filter on it to eliminate that possiblity.


    To test the broken pickup theory....put two extra quarts into the engine with it running. That will get the oil higher in the pan. If it makes it past 3000 then you know where the problem is. 1/2 quart won't do the job. Drain out the extra oil after you finish the test.

    -John
    RestorationMarine.com

    ASE Master Mechanic

    1994 -370 Express Cruiser
    Washington, D.C.

  7. #7
    Join Date
    Jun 2010
    Location
    Williamsport, PA
    Boat
    Sea Ray & Glastron Carlson
    Details
    1990 270 Sundancer, 2003 Ford Excursion 4x4 Limited
    Engine(s)
    454 merCruiser w/Bravo 1
    Posts
    1,862

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    Quote Originally Posted by PlayDate View Post
    Ok....before you pull the motor let me suggest something simple.

    What you have said:
    1) is that you never take your boat over 2800 rpms and everything is fine up to that point.
    2) On the one time you go over 3000 rpms the pressure drops to zero
    3) A mechanical gauge shows the same thing
    4) Oil pressure returns to normal below 3000 rpms.

    So you are dealing with a problem that most likely has been hidden from view for some time because you never went above 2800 rpms.

    There are only a few basic things that can cause what you are experiencing but the symptom is that the oil pan is going empty at 3000 rpms which is causing the drop in pressure.

    1) Broken oil pickup....separated from oil pump....basically runs out of oil
    2) Broken oil pump pressure spring (unlikely because pressure would not be 50 pounds)
    3) Bad oil pump drive mechanism (unlikely because it would get worse and eventually start losing pressure below 3000)
    4) Bad bypass on the oil filter (what kind of oil filters do you use?)

    Some oil filters use bypasses which open if the filter experiences too much pressure from the oil pump. If it opens...pressure drops. Put a mercruiser filter on it to eliminate that possiblity.


    To test the broken pickup theory....put two extra quarts into the engine with it running. That will get the oil higher in the pan. If it makes it past 3000 then you know where the problem is. 1/2 quart won't do the job. Drain out the extra oil after you finish the test.

    -John
    All great suggestions!

  8. #8
    Join Date
    Nov 2009
    Location
    SF BAY AREA
    Boat
    Sea Ray
    Details
    2003 410DA, 2004 C14 Caribe
    Engine(s)
    CAT 3126TA's 350HP/ 50HP Honda
    Posts
    6,497

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    Also, it seems strange that you are running those engines at such a low RPM normally. I would think you are barely on plane at those RPM's and not getting the optimum efficiency?

  9. #9
    Join Date
    Nov 2007
    Location
    MacRay Harbor, MI / Cedar Point, OH / Miami, FL
    Boat
    SeaRay
    Details
    1997 400DA / 1999 280BR "Project"
    Engine(s)
    340HP 7.4 Mercruisers / Twin 250HP Merc 350's w/ Alphas
    Posts
    1,611

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    Quote Originally Posted by PlayDate View Post
    4) Bad bypass on the oil filter (what kind of oil filters do you use?)

    Some oil filters use bypasses which open if the filter experiences too much pressure from the oil pump. If it opens...pressure drops. Put a mercruiser filter on it to eliminate that possibility.
    I wondered about this one - it ended up being the cause in some similar threads here, and it would be the easiest and cheapest place to start.

    1997 400DA
    340 HP Merc 7.4L Bluewaters
    7.0 BCG Wester-beast, Hurth V-drives

  10. #10
    Join Date
    May 2011
    Location
    Lake Erie Ohio
    Boat
    Sea Ray
    Details
    1989 Sea Ray 340 DA
    Engine(s)
    twin 454 Mercs
    Posts
    4,127

    Re: EXPLITIVE continued... Over 3000rpms oil pressure drops under 10LBS Bluewater 454

    I use wix filters on them...

    Thanks all...

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