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Thread: Oil pressure

  1. #1
    Join Date
    Mar 2009
    Location
    Dresden, Maine, United States
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    312

    Default Oil pressure

    Ok guys, I have an odd one for you. My boat has a chevy 270 (350 cu/in engine). I have a electric oil pressure gauge on it and when I start up cold it tells me I have 75 to 80 pounds of pressure. When I would get up to 2200 rpms it is around 75 pounds, get up to 3200 rpm and it starts to bounce all over the place. I then decided to put an mechanical gauge on as well. Start up and the electric gauge gave the same readings but the mechanical gauge would read 55 pounds. I would head out and run up to 2200 rpm and the mechanical gauge would read 25 lbs and the electric 75 lbs. increase the rpms to 3200 and the electric one stayed the same and the mechanical one would drop to around 10 lbs. There is no knocking or any noise when I get up in rpms.

    I am running 10/30 oil. The motor only has 58 hours on it. Any thoughts? One fellow suggested that the pressure relief valve where the oil filter screws on may be bad, The oil pan is a 5 qt model. I am at a loss and await every ones sage advice.

    Paul

  2. #2

    Default Re: Oil pressure

    That is a strange one. We tend to believe mechanical gauges but your electrical gauge has the more realistic numbers. Is the mechanical gauge plumbed next to the electrical sender ? Recommend trying another mechanical gauge. Needless to say, oil pressure is serious.

  3. #3
    Join Date
    Sep 2008
    Location
    Maryland - USA
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    Default Re: Oil pressure

    Quote Originally Posted by missnancy View Post
    ....The motor only has 58 hours on it.....
    Paul
    10/30 is a bit on on 'light side' regarding viscosity - what does the source of the engine have to say about viscosity?

    Pre-Y2K (old stuff), the rule of thumb was 10PSI of oil pressure for every 1000 rpm (@ operating temp)...having high pressure when cold is normal as is a drop as things warm up...

  4. #4
    Join Date
    Mar 2009
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    Dresden, Maine, United States
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    Default Re: Oil pressure

    The gauges are on a tee. What would be a better set up?

  5. #5
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default Re: Oil pressure

    "bouncing" oil pressure doesn't sound like a mechanical defect in the engine. Is it possible the oil level is very low or very high? At least one of your gauges appears defective.

  6. #6
    Join Date
    Mar 2009
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    Dresden, Maine, United States
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    Default Re: Oil pressure

    I just replaced the Mechanical gauge last week. The electrical gauge and sending unit last year

  7. #7

    Default Re: Oil pressure

    Try getting rid of the "T". Find 2 separate places to tap in, by distributor and one by oil filter. Put in fresh oil, straight 30 or 15w40. Is this a new issue? has anybody been inside the engine? Sounds like pan emptying out and not having good oil return from somewhere causing pump to run dry. Have seen oil pick up come loose from pump before causing weird oil psi problems. Also make sure you have the correct amount of oil in pan.

  8. #8
    Join Date
    Mar 2009
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    Dresden, Maine, United States
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    312

    Default Re: Oil pressure

    I was finally able to contact the fellow who did the reman and he recommends straight 40 weight for oil so I will be changing that out. I spoke to a local mechanic and he said that if the pick up was to close to the bottom of the pan then when the rpms are up the oil can't return quick enough. If I am Going to check that then I am going back to the deep oil pan that used to be on the engine. God I hate the idea of lifting the engine out again and all that goes with it.

    Any how having just hauled out and now on the hard this will be my winter project.

  9. #9
    Join Date
    Sep 2008
    Location
    Maryland - USA
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    Default Re: Oil pressure

    if the pickup is down low, it will pickup the oil as soon as its available.....and if that's the issue I'd be inclined to thing there isn't enough in the pan to start with.....did they put in a high volume pump?

  10. #10
    Join Date
    Aug 2008
    Location
    Fairport, NY
    Posts
    1,632

    Default Re: Oil pressure

    Quote Originally Posted by missnancy View Post
    I was finally able to contact the fellow who did the reman and he recommends straight 40 weight for oil so I will be changing that out. I spoke to a local mechanic and he said that if the pick up was to close to the bottom of the pan then when the rpms are up the oil can't return quick enough. If I am Going to check that then I am going back to the deep oil pan that used to be on the engine. God I hate the idea of lifting the engine out again and all that goes with it.

    Any how having just hauled out and now on the hard this will be my winter project.
    A cast aluminum deep pan is a good call. Tend to disagree with st 40 up there.

  11. #11
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    Mar 2009
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    Dresden, Maine, United States
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    Default Re: Oil pressure

    I looked things up and yes it is a high volume pump which is one more reason that in the spring I will be lifting the engine up to put the larger oil pan on her. Ugh!

  12. #12
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
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    9,191

    Default Re: Oil pressure

    .........................
    Quote Originally Posted by missnancy View Post
    Ok guys, I have an odd one for you. My boat has a chevy 270 (350 cu/in engine). I have a electric oil pressure gauge on it and when I start up cold it tells me I have 75 to 80 pounds of pressure. When I would get up to 2200 RPM it is around 75 pounds, get up to 3200 rpm and it starts to bounce all over the place. I then decided to put an mechanical gauge on as well. Start up and the electric gauge gave the same readings but the mechanical gauge would read 55 pounds. I would head out and run up to 2200 rpm and the mechanical gauge would read 25 lbs and the electric 75 lbs. increase the RPM to 3200 and the electric one stayed the same and the mechanical one would drop to around 10 lbs. There is no knocking or any noise when I get up in RPM.
    I would be more inclined to trust the mechanical gauge reading. The electric gauge or it's sending unit may be bad.

    I am running 10/30 oil. The motor only has 58 hours on it. Any thoughts?
    One fellow suggested that the pressure relief valve where the oil filter screws on may be bad,
    The relief valve at the filter is a by-pass. It is there to ensure continued oil flow in the event that the filter cartridge becomes saturated.
    It will not affect actual engine oil pressure as the engine sees it!
    The oil pan is a 5 qt model. I am at a loss and await every ones sage advice.

    Paul
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  13. #13
    Join Date
    Mar 2009
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    Dresden, Maine, United States
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    Default Re: Oil pressure

    Thanks Rick

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