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

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

  1. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    Not seeing anything in the water as far as a sheen or spots.

    It's a 98 with 613 hours currently.

    Cruising around 3800rpms roughly a qt an hour.

    Didn't get pictures of the plugs but from years of running 2000hp race cars Im pretty good at looking at spark plugs. And I didn't see anything that had me worried. I do have 1 hole that's got too much fuel. But I'm going to switch out that injector
     
  2. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    20w50
     
  3. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers

    Okay...no plug pictures, compression is okay, oil cooler replaced, no oil in the bilge and it is still using a quart of oil an hour. The only thing left is the engine. I'm not sure you would see oil on the water at cruise. Oil pressure builds with rpms and the amount of oil under the valve covers dramatically increases which if the valve seals are the issue would explain why it doesn't show up at idle or no wake speed. That said....if it was the valve seals/guides.....there are usually tell tale deposits on the plugs. And if that wasn't enough...the valve seals would have to be almost completely ineffective to burn a quart an hour.

    It just seems like we are missing something.
     
  4. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    im going to try and get some free time this weekend to pull the 1 injector out of the hole thats running fat and put one of the older injectors in there to clean up the 1 hole thats running fat.

    im going to try and borrow a friends small air compressor to do a leakdown on it also my compressor is just too big to drag out on the pier.

    and i agree 100%... im missing something
     
  5. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    I quart or oil in an hour.......
    If you’re in the mid 3k rpm range, probably burning about 15gal/hr gasoline.

    15 gallons of gas to 1 quart of oil is a 60:1 ratio. Is it possible that it is a relatively small amount of oil and can burn off without fouling the plugs or showing any signs of oil contamination?

    I know losing 1 quart per hour is a lot and not knowing the source is frustrating.
     
  6. aerobat77

    aerobat77 Active Member

    439
    Aug 12, 2014
    germany
    2006 240 DA Sundancer
    5.0 MPI / Bravo III
    1 qt / hour burning thru cylinders would result in visible blue smoke for sure . check the bilge twice and then check it again for an oil leak .

    you would also have a severe blow by from dead cylinders . when you remove the oil filler cap with engine running - does it blow severy out of the oil filler cap ?

    if not you are not burning this oil.
     
  7. Golfman25

    Golfman25 Active Member

    519
    Sep 12, 2009
    IL
    281
    V8
    I had that kind of oil coming from a valve cover. It was "hidden" and I only found it when a put my hand on it to pick something up. So I would start looking in hidden spots. Good luck.
     
  8. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    ive thought about degreasing the motor and seeing if anything pops up that i see

    never thought to run the motor with the cap off... but i'll check that thursday when im down there. i want to hose the bilge out and get everything cleaned up in there. i forgot to put a bucket under the raw water hose when i pumped all the sand out of the motor after hitting bottom. so i still gotta get all that out of it.

    so far ive put right around 18qts in the motor in the last 3 weeks... feel like id see it in the bilge by now if it was there.
     
  9. Rusted Nut

    Rusted Nut Member

    77
    Sep 21, 2016
    Lake Michigan
    1993 370DA
    Lots of engines
    Worn Exhaust guides or valve seals will pass a lot of oil and you will not see it on the plugs.
    Is this a new boat to you?
     
  10. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    My engine is the same year and the manual states that the engine will use 1 qt. of oil in 1-5 hours of running at or near full throttle.
     
  11. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    really? that seems crazy
     
  12. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Crazy high ? Also says that oil consumption will be a lot less at moderate speed
     
  13. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    yea im reading it now... 1qt every 5-15 hours under lower RPM range.
     
  14. MonacoMike

    MonacoMike Well-Known Member PLATINUM Sponsor

    Sep 15, 2009
    Indiana lakes and Lake Michigan
    2000 Cruisers 3870
    8.2 Mercs
    85 Sea Ray Monaco 197
    260hp Alpha 1
    My 502/8.2 manual says the same, but did not read that it applies to the 7.4. It is stated that the forged pistons need greater ring clearance due to the heat of the high performance 8.2 resulting in oil use.

    I recently put 10 hours on for a trip and used a quart in each. Just as a friend that has had his 8.2's since new told me I would, it was that way from the factory.

    MM
     
  15. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    the 7.4 mag has forged pistons . Just had my motor freshened up and the machine shop ordered oversized rings and file fit them, I do say I'm using quite a bit less oil than last year. Using half of what you just mentioned
     
  16. Island Time Buffalo

    Island Time Buffalo Member

    180
    Aug 19, 2014
    Grand Island, NY
    380 Sundancer 1999.
    7.4 Horizons
    Yup, 7.4's eat oil like candy. I cruise at 3300 (3400 sometimes) and go through a lot of oil. I gotta say, though, running 3800 seems pretty hot for 7.4's. I wouldn't run that hot.
     
  17. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    this is a non MAG MPI.

    ive heard these motors should go to 4800... so 3800 didnt seem that high. im going out saturday maybe i'll try running them a lil slower and see what happens
     
  18. Creekwood

    Creekwood Well-Known Member GOLD Sponsor

    Apr 26, 2009
    Oakville and Georgian Bay, Ontario
    '97 330 Sundancer, Raymarine C80 suite with radar, Mercury 310 Hypalon w/8hp Yammie 2stk
    2X 454 carbs w/ vDrives
    My 7.4s don't burn anywhere near that much oil. I cruise at about 3400 rpm/30mph and maybe add on quart to the port engine and none to the starboard engine over a roughly 50 hr operating season. I am at about 900 hrs on them.
     
  19. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    You still haven't said if this oil usage is new or has been existing.
     
  20. SrtThis

    SrtThis Member

    57
    Feb 20, 2019
    Maryland
    270 SE sundancer
    7.4 MPI w/bravo III
    first year we have had this boat so hard to say. im assuming its new
     

Share This Page

Show Sidebar