Mercruiser 7.4 454 CI loss of oil pressure

Discussion in 'Mechanic Recommendation Forum' started by Mike Siner, Nov 4, 2020.

  1. PlayDate

    PlayDate Well-Known Member

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

    Again...the conditions have changed since the sea trail and when the problem first appeared. The owner changed the oil on both engines. Like 99.9% of us he did not measure how much oil he took out only how much he put in (8 quarts). If it is an oil capacity issue and both pickups were the same.....it would now appear on both engines. If the pickups are different it may happen on only one engine.

    I'll bet the previous owner knows what is going on.
     
  2. joeyleggz

    joeyleggz Well-Known Member

    804
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    I'll bet the previous owner knows what is going on.[/QUOTE]

    Ill agree on that , the previous owner has the details ...All things being equal something might be letting go in the motor
     
    scoflaw likes this.
  3. joeyleggz

    joeyleggz Well-Known Member

    804
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
  4. Mike Siner

    Mike Siner Member

    44
    Oct 20, 2020
    1992 Sea Ray 350 Express Bridge
    454 Mercruiser CI
    I found these pictures on the web, but this is what my oil plans look like. They are grooved which was strange to me. possible oil pan 1.jpg possible oil pan 2.jpg possible oil pan 3.jpg
     
    joeyleggz likes this.
  5. joeyleggz

    joeyleggz Well-Known Member

    804
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
  6. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Late 1980s to 1990 Mercruiser vintage (Cast aluminum oil pan part # mercruiser 47552)..... They made a couple of different aluminum cast models but that looks like a 7 quart pan. At 8 quarts (allowing for a remote oil filter) in each engine you should be good to go unless there is a problem with the pickup.
     
  7. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Any update?
     
  8. Mike Siner

    Mike Siner Member

    44
    Oct 20, 2020
    1992 Sea Ray 350 Express Bridge
    454 Mercruiser CI
    Update. I added an additional quart of oil and the engine stabilized up to 2900 RPMs but once I got above 3000 RPMs the oil pressure dropped back down to 10+/-. Once I dropped the RPMs to below 3000 the oil pressures came back up to 40+ and stayed steady. I am thinking that I have a faulty oil pump?
     
  9. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Based on your previous comments it would appear that adding more oil helped by 500 rpm or so.

    That leaves you with:

    1) High volume pump that is pumping the pan dry
    2) The pickup has fallen out of the pump which means it cavitates
    3) The pump or pump shaft has a problem with it.

    So you are back to your original solution which was to pull the pan off and replace the pump. That is a serious pain to do. No word from the previous owner?
     
  10. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    When you get that far into it pop off some bearing caps for a look/see
     
  11. northern

    northern Well-Known Member

    Jan 17, 2007
    Anacortes Washington
    380 Aft Cabin 1989 Charts Timezero radar Furuno
    Twin 454 strait shaft
    I would add one more quart of oil and see what happens. If oil pressure drops you are probably frothing the oil. If that does not help do the oil cooler next. They are $100 for cooler plus cost of the hoes and connecting oil lines to the oil filter. You can only do it if you have a remote oil filter. Or you can go slow 2900 RPM should be good for most of your travel. At 3,200 RPM the 4 barrels click in and you will go to 50GPH around 3,800 RPM.
     
  12. Mike Siner

    Mike Siner Member

    44
    Oct 20, 2020
    1992 Sea Ray 350 Express Bridge
    454 Mercruiser CI
    Any chance that these symptoms could be a main-bearing? There aren't any squealing or grinding noises coming from the engine. The oil analysis didn't show metal in the old oil.
     
  13. PlayDate

    PlayDate Well-Known Member

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

    I think you are at the "it doesn't matter" point in the diagnostic. Without input from the previous owner......the only alternative is to pull the engine and see what is really going on. Every symptom you describe shows the engine is running out of oil (or losing pressure) but who knows until you pull the pan.

    I hoped it was something simple because pulling the engine on your boat is a PITA.

    Alternatively, you can enjoy the boat for a while cruising around at less than 2,000 rpm until you want to take on dealing with it. Your signature does not say where you boat but nothing stops you from using the boat. That way you can address it on your terms by finding a replacement engine and having everything ready to go so that downtime is minimized. Nothing is worse than pulling an engine without a plan to replace it. You can lose months trying to sort out options.
     
    HawkX66, Mike Siner and Chris-380 like this.
  14. Mike Siner

    Mike Siner Member

    44
    Oct 20, 2020
    1992 Sea Ray 350 Express Bridge
    454 Mercruiser CI
    Thanks. I am taking your advice and planning this out to minimize downtime and boatyard cost. I keep the boat just north of Tampa, FL, and this time of year the yards are packed, and mechanics are busy. This is my first big boat and I've been making all the rookie mistakes. I blew the 5.0 Westerbeke generator with only 99 hours on it by flushing it incorrectly. So I have that expense to deal with as well. I love the boat and being on the water but I may have to start robbing banks to keep up with it...lol.
     
    Chris-380 and PlayDate like this.
  15. northern

    northern Well-Known Member

    Jan 17, 2007
    Anacortes Washington
    380 Aft Cabin 1989 Charts Timezero radar Furuno
    Twin 454 strait shaft
    New generator installed is 14K New engine installed is about the same so all total with 2 new engines and a generator you are at 50K. Only you know if it is worth the cost. If you have not had a very detail inspection of the entire boat to determine: stringer, bulk heads, transom, deck, electrical and electronic you may want to get that done before you spend any money on the boat. We were quoted 45K to replace generator, engines and rework transmissions 2 years ago. Our boat is valued at 50K.
     
  16. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Also a couple of things to ponder.
    That engine will get worst before it gets better
    As it sits now it's a very rebuildable motor. Once the banging starts, not so much.
     
    HawkX66, Chris-380 and joeyleggz like this.
  17. joeyleggz

    joeyleggz Well-Known Member

    804
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    Exactly stop running the motor and start ripping into it
     
  18. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Why can't he enjoy the boat for a while?

    Why does he have to take his new purchase, have it hauled and blocked.....then spend the next six months not using it? Rebuilding a 28 year old engine in my opinion will require everything to be done. At that point, it makes far more sense to have a rebuilt engine at least lined up so when he is ready....the time out of water is reduced. Based on recent history.....unless you have an in with a qualified machine shop.....a rebuilt motor from Jasper will be the same costs perhaps less.

    I would get depressed pretty quickly if I couldn't enjoy it for a while before I put it back on land and dealt with the engine and a generator. I just don't see the downside of a few months of use just to build up positive side of owning the boat.
     
  19. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Agree but 3 months aren't guaranteed. Might be 1 more trip, who knows. As it sits it's a non planing boat. If he's OK with idling around go for it.
     
  20. joeyleggz

    joeyleggz Well-Known Member

    804
    Jan 15, 2013
    long island
    current boat: 1997 sea ray 330 express cruiser
    twin 454's efi
    to each his own , I wouldn’t feel comfortable running my boat at length restricted to a certain RPM for fear that you might blow the motor sometimes you need to exercise power in your boat to get out of sticky situations while you are out on the water I know I require that just coming in and out of inlets sometimes. If the problem is fixing an oil pump or pick up tube I would want to confirm and get it done as soon as possible because the alternative is if there is nothing wrong internally with the motor not fixing it only puts undue stress on the mains why take a chance of popping the whole motor over an oil pump?
    The fact that he already blew his generator why take a chance of finishing off the motor or motors ? now that’s pretty depressing
     
    Last edited: Jan 13, 2021
    HawkX66 and tdschafer like this.

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