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Low Oil pressure 454 Mag

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  • Low Oil pressure 454 Mag

    I've got a 454 with about 150 hrs on it. Running 15-40 wt Rotella only about40 psi 3000rpm cold oil, only about 20 psi hot, practically zero psi when hot idle. No noises from motor, runs ok, but have lost about 8 mph off the top end from last season (48 down to 40). Motor runs about 150 deg, never oveheats. I switched to KN high $$$ oil filter, no difference, and yes I tried a mech oil gauge to verify readings, and it was identical to elec gauge. Is my motor dying a slow death? I've never had a running engine with such low oil press readings. This is an 89 Chaparral 2550 SX

  • #2
    Re: Low Oil pressure 454 Mag

    Time for a new oil pump.
    Bearing clearances regulates oil pressure.
    One or the other or both.
    From Mercruiser:
    Anyone who uses a service procedure and/or tool, which is not recommended by the manufacturer, first must completely satisfy himself that neither his nor the product’s safety will be endangered by the service procedure selected.


    • #3
      Re: Low Oil pressure 454 Mag

      Originally posted by stinger222 View Post
      Running 15-40 wt Rotella
      Should be running straight 40W, not 15W-40.
      Can get Rotella 40W at O'Reilly's or Delo 40W at West Marine.


      • #4
        Re: Low Oil pressure 454 Mag

        As Shrub says, running multi-weight automotive oils in a boat is not generally a good idea:

        Multi-grade ratings of petroleum oils are made by adding polymeric plastic thickeners to an oil with a very light viscosity. An example of this is 10W-40 oil, which is created by thickening a 10W oil to the equivalent of an SAE 40W oil at 212 degrees F. The reason a 10W oil is used is to maintain low viscosity at low temperatures; this helps with engine startup and cold weather performance. The thickeners increase viscosity at higher temperatures. Unfortunately, when the large molecules of the polymer thickeners encounter a high-stress area, like a bearing, these big molecules tend to align themselves to create a path of least resistance. This greatly reduces the film strength of the oil; the result can be an apparent viscosity that is much lower than the viscosity listed on the container. In fact, a standard 10W-40 oil, when subjected to high stress, may perform to SAE 20 specifications, simply because the added thickeners cannot cope with the additional stress.
        Latest oil recomendations from Merc:

        Pay close attention to the NOTE just above the white chart. However, if you don't like the manufacturer's recommendations, run whatever you feel like. You'll find plenty of people to support whatever you choose if that's what it takes to make you feel good!
        Any opinions expressed above are worth exactly what you paid for them!


        • #5
          Re: Low Oil pressure 454 Mag

          not to discount what the others have said but i doubt your oil viscosity is your problem.

          this is what the mercuriser manual says for you problem

          Verify with an automotive test gauge. Refer to
          Section 4D for instrument testing.
          Thin or diluted oil
          Oil broken down; contains water or gas; wrong
          viscosity; engine running too hot or too cold;
          excessive idling in cold water (condensation)
          Oil pump
          Relief valve stuck open; pickup tube restricted;
          worn parts in oil pump; air leak on suction side of
          oil pump or pickup oil tube
          Oil leak can be internal or external Oil passage plugs leaking, cracked or porous
          cylinder block
          Excessive bearing clearance Cam bearings, main bearings, rod bearings
          Women are Angels.


          • #6
            Re: Low Oil pressure 454 Mag

            I'm sorry, but I'm missing something perhaps... and not trying to start an oil arguement thread... It is highly unlikely that Rotella T 15-40 does not easily satisfy all of the requirements for NMMA and FC-W ratings. It is a heavy duty diesel and offroad oul with one of the most complete detergent and anti-scuff additive packages of any of the widely available oils on the market. It is a quality oil and what my engine builder recommends especially in engines with flat tappet camshafts. It is probably a little thin for standard marine engine aplications and change intervals, but it is not thin enough to show the problem that you're having.

            You've got a pressure "leak" or other problem as mentioned above... somewhere...
            Just another moron with a computer and too much time on his hands...

            typical rainy afternoon on the river... http://www.youtube.com/watch?v=8Izi3v75jTs

            more recent, amateur camera operator for sure!... http://www.youtube.com/watch?v=EHoXsQc6644


            • #7
              Re: Low Oil pressure 454 Mag

              thanks for the replies...I have always used this oil on my boats and have never had a problem. I took off the port side valve cover to check things out, fired up the engine, plenty of oil squirting around. Is it normal to have a small river of oil flowing back down the outside edge of the head towards the back while the motor is running. I've never looked at a motor running with a valve cover off.


              • #8
                Re: Low Oil pressure 454 Mag

                Yes, it's typical to have oil flowing back. That needs to happen or it fills up in the valve covers.
                1989 Starcraft 171S Select "Cap'n Crunch" / OMC Cobra 4.3 V6 / 432APRMED

                If you're going to keep that OMC Cobra, please for the love of everything good in the world, get an OMC factory service manual. Not a Clymers, Not a SELOC. You can find them on eBay.

                My boat repair website: http://transomfix.dcpolk.com



                • #9
                  Re: Low Oil pressure 454 Mag

                  I cut open oil filter from recent change. Some metal shavings in the bottom. I'm guessing there shouldn't be any metal in there at all.


                  • #10
                    Re: Low Oil pressure 454 Mag

                    I cut open oil filter from recent change. Some metal shavings in the bottom. I'm guessing there shouldn't be any metal in there at all.
                    Ayuh,... That's correct,... I'd Guess you're probably loosing a main bearing or 2....


                    • #11
                      Re: Low Oil pressure 454 Mag

                      10 psi today at 3000 rpm with the engine warmed up. I am going to take it easy and try to make it to July 4th weekend. In the meantime I'll keep the Sea tow # handy. After the 4th I'm pulling the motor to rebuild and stroke to 496, upgrade to roller motor. Any oil recommendations to buy me insurance for 2 more weekends? Do they make straight 50 wt oil? Someone told me to try Lucas oil additive.


                      • #12
                        Re: Low Oil pressure 454 Mag

                        sudden loss of oil psi + metal in the filter

                        dont take a chance. motor needs to come out and find out whats wrong with it. if you blow it up at best you lose your core or good chance you'll ruin block for rebuild. worst case you drop a rod out the bottom of the pan and bust a hole in the bottom of your boat. not likely but possiable.
                        Women are Angels.


                        • #13
                          Re: Low Oil pressure 454 Mag

                          Ran this by my mechanic. He said that if the oil pressure was really that close to zero at idle, there would be quite a bit of valvetrain noise, given the top end would feel the effects first of low oil pressure first. The fact that there was a pronounced "river" of oil flowing along the edge of the cyl head at idle along with oil squirting everywhere with the valve cover off leads him to believe there might just be a restriction somewhere near the oil port where I am getting the pressure readings (with elec or manual gauge). I changed the oil to straight 50w valvoline along with 2 qts Lucas oil stabilizer. I'm going to run it the rest of the summer and be easy on it and then rebuild over winter. If I smoke it before then I guess I'll be buying a 502 crate motor!!!


                          • #14
                            Re: Low Oil pressure 454 Mag

                            well its Aug 15th, still only 10-20 psi hot oil press, have been using the boat every weekend. Now the goal is make it to Labor Day weekend? No noise from motor at all.

                            The oil pressure dropoff back in May was also accompanied by a dropoff in top end performance, unless it was a coincidence. Top end went from 45 to about 35...something is going on, but the thing keeps running!


                            • #15
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                              Re: Low Oil pressure 454 Mag

                              i'd pull it....

                              you could have a spun bearing more likely a main bearing...

                              you wont hear any top end noise with low oil pressure because the way the oil system works it does the top end 1st the and the bearings/crank last...

                              when you run out of oil the first thing to get shorted is the rods/crank....thats the way it works...the mechanic you talked to should know this....

                              this is how it keeps the lifters pumped up...it gets those first then the mains...it is possible that the oil bypass in the filter adapter has busted as well...this is common on motors that run full bore with thick oil...

                              I would pull the filter and pull the adapter and look at the bypass...I just changed on in a engine where the spring broke from heavy oil...

                              if the bypass sticks open the oil gets in a loop and never goes into the engine...it goes from the pan to the pump and right backj into the pan...

                              if the bypass is fine I would pull the engine and start checking it out...

                              a 454 can live on 4psi as long as it isnt beat to death...

                              there are several things that can lead to low oil pressure...loss of bearing clearance and thrust surface...if it eats the thrust bearing presure and go to...

                              spun cam bearing or any one of the mains....if a main spins most of the time you wont hear it....

                              best bet is to check the bypass 1st that is the cheapest route...