High oil consumption on one engine

Discussion in 'General Maintenance/Repair Questions' started by YeOldeStonecat, Aug 26, 2019.

  1. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    So as I'm tweaking things on the second summer of our "new to us" boat (the '97 300DA)....I'm getting bothered by what I think is high oil consumption on the starboard engine.

    Brief history/background.
    *Purchased boat Spring 2018.

    *Last summer, and this summer, the starboard engine is still thirsty for oil. Last year I noted the original owner has used 10-40 oil. I changed oil twice last year with 25-40 Quicksilver oil...hoping the thirst for oil would slow down with the proper thicker stuff. It didn't.

    Plus look OK. No drips in the bilge, it's not a leak.

    Engine hours, ~570 port, ~660 starboard. 5.7 260 hp Mercruisers.

    I topped off oil before a trip to Greenport LI a few weeks ago, when we returned, the ~4 hour cruise consumed 1/2 qt of oil in the starboard engine. Probably not even an 1/8th of a qt in the port engine. My cruising speed for most of it was 3300-3400 rpm. I rarely take her about 4k rpm...probably twice this summer, and not for long.

    Engine temps decent...165-170.

    I have read that PCV valves can affect oil consumption. I "think" mine are just elbows there with a hose to the flame arrest/air intake...but will check.

    She gives nothing visible for exhaust...no smoke.
    No oil sheen in exhaust water existing.
    There is a very slight blackening around the starboard engines above water exhaust exit...very slight, compared to the port side which is nice 'n clean white.

    I'm fearing valve seats I suppose? Not sure what a top end job runs. ugh.

    Until THEN..has anyone in a similar situation found some relief in going with a thick straight weight? We don't run her in cold weather, she's not year round up there...up on the hard during winter.
     
    Last edited: Aug 26, 2019
  2. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Try changing the valve seals, can be done with just removing the valve cover. Try some 20-50 vr1. Probably your piston rings. Look for excessive blowby coming out of the valve cover breathers.
     
  3. Zim

    Zim Active Member

    189
    Jan 16, 2018
    2012 Sea ray sundancer 310
    Twin merc
    Compression seems real good. I'm leaning towards valve stem seals myself. How do the spark plugs look?
     
  4. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Was that a misprint on the compression numbers, saying that's your port engine ?
    If it was the stbd numbers, they are high for a non-vortec engine and would be an indication that there is an excess of oil boosting the reading, which would point to rings.
     
  5. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    Dangit....that's what I get for posting before more coffee. Good catch. Sorry...yeah, that was for port engine which is running fine. I could have sworn when we purchased it work was done on the starboard engine including a compression check...but I was apparently incorrect...it was the port engine which is running fine now. But during sea trials port engine was backfiring badly and I had the yard do a compression check plus change rotor/cap/wires.

    So...OK...I have no compression check numbers to go on for the starboard engine. Will get some done.
     
  6. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    Quite decent....not oily or fouled.
     
  7. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    Re: valve seals. I'm somewhat mechanically inclined...replaced the manifolds/risers this past spring. Do own brakes on cars/trucks, oil changes, etc. Have pulled the rocker boxes off of old Harleys to redo gaskets. So...doing valve seals....difficult levels? Special tools required?

    Will try some 20-50 oil..or 25-50 if I find it. Guessing straight 60 weight like I used to use in my old Harley Shovelhead is too thick. ;/

    No "breathers" on the valve covers...only devices are 1) Oil filler cap, 2) on same bank...the breather hose going to flame arrestor/intake. Might be just an elbow, or could be a PCV valve....I'll examine it closely next week. But where it goes come to the flame arrestor/intake..that area is just "slightly" black...does not look like oil is splattered like I'd imagine if there was a lot of positive pressure in the valve cover/case.
     
  8. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Yes that elbow. If it's puffing oil like a chimney when disconnected its rings.
    So the valve seals...get the piston at top dead center, chuck up some air into the spark plug hole, with your compression tester adapter, and remove the 2 rocker arms. they make a pry bar like tool for like $10 you attach to the rocker stud and you put pressure on it to remove your valve springs. Then R/R the seal. You can probably find a youtube vid on it, simple stuff.
     
    YeOldeStonecat likes this.
  9. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    I'm thinking since it's relatively clean around that elbow..and the end of the hose going to the air intake...we're good on the rings. So yeah I'll dig up some "how to" videos on you bube. Thanks!
     
  10. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    k-d no. 912 is the cheap prybar for the springs. ebay $16
     
    YeOldeStonecat likes this.
  11. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Order up a set of retainers (or keepers). There are 32 of them on the motor, Murphy’s law will dictate that you will drop one and lose it if you don’t have any spares.

    Order some extras. (That should guarantee that you don’t need them!)
     
    YeOldeStonecat likes this.
  12. 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
    Whooo! Slow down for a minute. First of all there are no PVC valves on a marine engine, only breather tubes that direct engine blow by from the valve cover to the top of the engine intake. If the amount of oil accumulation on the two flame arrestors are the same then rings are not the problem. Yes it could be valves seal but I would be willing to bet there is a pinhole leak in the starboard engine oil cooler. That would account for both the excess oil consumption and the oil around the exhaust outlet. If it were rings or valves seals the engine would be burning off most of the excess and you would not see oil accumulation around the exhaust port.
     
  13. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Well they most certainly do put pcv's on marine engines, and the sbc engines usually don't have oil coolers.

    So...
     
    cfd95 likes this.
  14. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    I'll take pics of the exhaust ports..comparing port 'n starboard. The exhaust port isn't "wet oil" dirty...nor slippery. It's just barely tinged/sooted enough to notice. Not black or horrible looking by any means, it's not all sooty like an old coal locomotive. Just trying to make as many observations as I can to give more details.

    Here are 2 pics....first one showing that breather tube..source and destination.
    Second one showing closer up of that "valve"..either PCB...or just elbow....

    engine1.JPG Engine2.JPG
     
  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 2nd pic looks like a pcv. Go to Mercruiserparts .com, punch in your engine # and look at the diagrams yourself to see what you have.

    Instead of observing from the outside. You warm the engine up fully and pull that pcv out of the valve cover and see how much oil vapor is coming out when its hot and running. The pcv could easily vacuum the blowby out without leaving a trace on the outside. The valve will also be plumbed to the manifold and not the flame arrestor
     
    YeOldeStonecat likes this.
  16. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    I thank everyone for their input and time/knowledge.
    Should be at the boat this Thursday night, will take "up close" pics of what that PCV/elbow, also where it fixes to the intake. And I'll hit Mercruiserparts.com and see what it tells me.
     
  17. cfd95

    cfd95 Member

    327
    Nov 5, 2013
    Northport Long Island
    2002 310 Sundancer
    350 Horizons
    V Drives
    i have them(PCV) on my 350 EFI motors and no oil coolers.
     
  18. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    So a few weeks later I finally get around to uploading pics. I changed them out not long after posting this, pulled them the day I took these pics...got the part number, went down to NAPA...got 2 of them for $8.84.

    These pics show the old ones...pre-change. The starboard engine...note the hole the PCV goes in is a bit rusty...and the PCV itself is bent. So I figure "Ahh..since it's bent, probably broken...so my oil consumption will be gone!" However in looking at the PCVs..and shaking them, they rattle. So if they rattle, guess that means they are functional...and I cannot blame them for oil loss.

    Regardless, cheap enough, so I swapped 'em. The port engine had a newer looking PCV..and the hole in the valve cover was clean, smooth paint. But both are swapped with new now.

    I did 2x runs with the boat, 1x short run 2x weekends ago up to Lord Cove by East Haddam, and last weekend...a 4x (2x hours each way) hour run from Deep River to Noank...Fords Lobster, and out around RAM island. On the way back several sprints at steady 4k rpms. So that was more hours, and more RPMs...than the run to Greenport LI. This weekend I'll pull my rear lounge chairs and deck plates and pull the dipstick on the starboard engine and I'm curious what the oil reading will be.

    PCV1.jpg PCV2.jpg PCV3.jpg PCV4.jpg PCV5.jpg PCV6.jpg
     
  19. YeOldeStonecat

    YeOldeStonecat Active Member

    258
    Jun 10, 2018
    Waterford, CT
    '97 300 DA "Me-Shell"
    Twin 5.7 V-Drive
    Whelp..been a while. Took a bit to get her hauled and staged for winterization/wrappage. Requested the yard to a compression test on the starboard engine. Head mechanic just called me..said they fired up the engines on a very still day and he saw a tiny bit of rainbow on the water surface. He said at that point he hoped I had oil coolers...pulled the deck ...and...yup no oil coolers.

    He ran a compression check, said most cyls were around 160 within some variance, but one back was a little lower..and one of those cylinders in that bank was ~120.

    As he was pulling the plugs to do the comp check..he noted most were a little oily.
    I asked for his advice..he said he could run a leakdown test, it can help point if more rings or top end.

    I asked him for what he thinks the best course of action is, he said a reman "long block"...run around 10k.

    YIKES! :(
    I think next summer I'll shift to straight weight oil...40 or maybe 50...and just get through the summer...saving for a reman the following year.

    Open to suggestions of temp snake oil miracle cure all fixes to slow down that oil burn. Heh.
     

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