Logo
Results 1 to 10 of 10
  1. #1

    Question Mercruiser 3.0 blow by/ turn engine manually

    Hey everyone, I have a 2001 bay liner with a mercruiser 3.0. Engine is a remanufactured motor installed in 2017. On my 2nd trip this year I noticed oil in the bilge being pushed out through the dipstick. Seems like slot of blow by coming from oil cap as well. Compression test reads 165psi on all cylinders cold. I havenít done a leak down test because I donít know how to spin the motor manually to get piston to TDC on compression stroke. The crank pulley is blocked by the motor mount and the water pump and alternator pulleys do not have enough grip with the belt to turn the engine. Is my only option to try and bump it to the correct spot with the starter or is there another way? Iím replacing the pcv valve and hose with something bigger to try and relive the pressure and stop oil leak, but Iím worried it wonít be enough and Iíd like to know the internal condition of my motor. Any advice is appreciated.

  2. #2
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    3,620

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    I usually connect a remote start switch to the engine so I can "bump it" while I'm at the engine instead of @ the helm. Connect the remote start switch between +12 and the coil ( small terminal (non grounded one) of the solenoid)
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280

  3. #3
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    5,868

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    If il is coming out of dipstick tube I would first confirm oil level with engine off. If way over level then either too much oil or water in engine.

    If blow by is heavy and the oil level is ok then I would suspect a possible oil control ring break. That is the bottom ring of then three on the piston.

    pull the plugs and see what they look like. If oil ring is broken one would look really black and oil soaked.

    Compression is controlled by valves seating properly and the two top rings on piston sealing during compression stroke.

    What did you plugs look like when you did compression test?
    Last edited by kghost; 06-15-2021 at 01:06 PM.
    Jack
    Mass.

  4. #4
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    5,868

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    Quote Originally Posted by sandkicker View Post
    I usually connect a remote start switch to the engine so I can "bump it" while I'm at the engine instead of @ the helm. Connect the remote start switch between +12 and the coil ( small terminal (non grounded one) of the solenoid)
    Connect remote jumper to Battey + and yellow with red stripe wire on either starter solenoid or slave solenoid to CRANK the engine ONLY (KEY OFF)
    Jack
    Mass.

  5. #5
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    5,868

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    """"I’m replacing the pcv valve and hose with something bigger to try and relive the pressure and stop oil leak,"""

    wont help or change your issue so dont waste your time
    Jack
    Mass.

  6. #6

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    The plugs were not terrible, you could tell they haven’t been changed in a while but they were not oil soaked. I bought the boat last summer so I have no idea of the maintenance before hand. Also the oil level is within spec according to the dipstick. Did not have this issue on the first ride this spring but noticed it on the second. It was a noticeable amount of oil in the bilge. Also no water in the engine or oil. There is no smoke coming from the oil cap and no oil is blowing through the pcv vent line. Although I think the pcv valve or connected hoses were partially blocked which is why I’m replacing those items. I will be installing them today but the only time I have oil come from the dipstick is under a load so I’ll have to go to the lake to get any more updates from that. I will try to get a leak down test done this weekend.

  7. #7

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    So can a motor build great compression and still fail a leak down test?

  8. #8
    Join Date
    Jul 2008
    Location
    Northboro, Ma, USA
    Posts
    5,868

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    Yes but not typical.

    Your last reply has a lot more info. Maybe try to add all the details in a first post!!

    If no excess oil and plugs look normal and only blow by then
    My first thought is a bad/stuck ring.
    Because there are two rings it may show good compression.
    A leak down test may show a more realist result.


    What is the oil pressure when running? Any idea?
    Jack
    Mass.

  9. #9

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    I don’t think my gauge is very accurate, it’s on the list to be replaced with the sending unit but it reads somewhere around 25psi

  10. #10
    Join Date
    Aug 2006
    Location
    SW Ohio, USA
    Posts
    10,459

    Default Re: Mercruiser 3.0 blow by/ turn engine manually

    Was the PCV valve plugged? I've seen oil blow out a dipstick when it was plugged.
    Fix minor things (replace wear items for preventative maintenance.) that cause major problems before they break.

Similar Threads

  1. Mercruiser 3.0l engine excessive blow by but good compression
    By Gavin147 in forum Mercruiser Sterndrive Forum
    Replies: 2
    Last Post: 06-23-2012, 06:00 PM
  2. fwc blow out on 2007 6.0 MPI engine
    By Schiffner in forum Crusader Marine Engine Forum
    Replies: 3
    Last Post: 02-15-2011, 07:46 PM
  3. Problem turning engine manually
    By wydeffinopen in forum Volvo Penta Gas Archive
    Replies: 3
    Last Post: 05-13-2007, 01:12 PM
  4. Manually Turn over 30L
    By russ0943 in forum Mercruiser Sterndrive Archive
    Replies: 11
    Last Post: 05-25-2006, 04:17 PM
  5. Manually Turn over 30L
    By russ0943 in forum Mercury Mariner Outboard Archive
    Replies: 0
    Last Post: 05-18-2006, 12:23 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •