7.4MPI oil loss... wheres it all going?!?!?!

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by SrtThis, Aug 2, 2019.

  1. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    A qt. an hour at 3800 is excessive for sure, but if it runs good, oil is cheap and it is summer.
     
  2. SrtThis

    SrtThis Member

    73
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    honestly thats kinda where i am with it at this point, i'll worry about it more once i pull the heads off to get the tops ends done.
     
  3. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    I'd be more inclined to think it's your 20 year old rings.
     
  4. SrtThis

    SrtThis Member

    73
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    could be for sure. more than likely i'll just pull the motor and go over the entire thing when it comes that time. my motor builder has 2 motors for my race car currently so it will be after those are done lol
     
  5. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 EC
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin 546s Plotter
    454 Crusaders
    My Crusader 454s were rebuilt 4 years ago with new cast pistons (.010 over), bearings, lifters, valves, mild performance camshaft, rockers and Melling oil pump. They now have about 180 hours and they have yet to consume oil. I'm a bit surprised at the oil consumption numbers being quoted here.
     
  6. MonacoMike

    MonacoMike Well-Known Member

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    2000 Cruisers 3870
    8.2 Mercs
    85 Sea Ray Monaco 197
    260hp Alpha 1
    Good engines, but completely different brand...

    MM
     
  7. SrtThis

    SrtThis Member

    73
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    updates... well... kinda

    ran out the rest of the season... STILL no idea where the oil is going.
     
  8. Getaway

    Getaway Active Member

    936
    Oct 13, 2010
    Bay City, Michigan
    1998 290DA Sundancer
    Lowrance electronics, Fishhawk, Scotty Downriggers
    BoatWheels Tri-Axle Trailer
    Single big block 454 MPI Mercruiser engine and Bravo III outdrive.
    Strange problem.

    My 1998 7.4 MPI went 105 hours last season and didn't even use 1 full quart of oil. She's got almost 800 hours on the motor and I cruise around 4000r's.

    FWIW, I use Brad Penn high zinc racing oil
     
  9. aerobat77

    aerobat77 Active Member

    452
    Aug 12, 2014
    germany
    2006 240 DA Sundancer
    5.0 MPI / Bravo III
    with the same use of oil the entire season ?
     
  10. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Out the tailpipe. It's not in the bilge and you replaced the oil cooler right ? Thought you were gonna rering this thing after your machine shop finished building your race engines.
     
  11. El Capitan

    El Capitan Active Member

    536
    Jul 9, 2014
    Chicago IL./Vero Beach, Fl
    1970 SRV 180 w 2.5L Mercruiser.
    2000 Ford Expedition Eddie Bauer
    120HP Mercruiser
    My bet it’s all blow-by. If cruise is 70% of WOT then you should be closer to 3200-3300 rpm on 7.4?

    I had 7.4 mercruiser w visible blow-by when pulling oil cap but it didn’t consume anywhere near what your getting.

    It rings.
     
  12. DWABoat

    DWABoat Active Member

    274
    Aug 13, 2019
    S Louisiana
    2001 280 Sundancer
    1989 220CC Cuddy Cabin
    Twin 4.3 w/Alpha Ones
    5.7 Mercruiser Alpha One
    Don’t know if my info will help, but...I bought a used 1995 Dodge p/u with the 318 years ago. Drove it normal for a few weeks no problem. No leaks. No smoke. No oil consumption. Towed my 4500 lb boat about 100 miles and my oil light came on. Fast forward a few weeks: the Oil Pan Gasket had blown out. It lies between the intake manifold and block. Under a load, the increased vacuum sucked oil directly from the pan and blew it out the exhaust. Normal driving did not create enough vacuum. The oil did not burn. No engine drips. It went right out the exhaust pipe. $1 gasket took a removal of the intake to fix. I am not sure if that engine is anything like yours. If you pulled an exhaust manifold and studied the inside of the exhaust, you may find clean oil.
     

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