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power trim fluid question: motor oil or hydraulic fluid?

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  • power trim fluid question: motor oil or hydraulic fluid?

    so i have been sorting out some power trim issues... and while cleaning nasty old oil/grease i found a sticker... from what my research shows it came off of the power trim unit... it says something about using only 10w-30 or 10w-40 motor oil....

    i have done some research.... and yes, these old units do use motor oil...
    well i have been using hydraulic fluid, and so was the previous owner, but it has been working fine lifting and lowering the motor...
    so my question is... should i start using motor oil? the unit was pretty contaminated with water from leaking threads, so im going to drain the whole system... and maybe now would be the time, if ever, to make the switch back to good old 10w-40....
    or should i continue to use hydraulic fluid?

    Thanks guys!

  • #2
    Re: power trim fluid question: motor oil or hydraulic fluid?

    well I just changed from atf to motor oil 2 days ago.... atf worked great but has a nasty habbit of making a thick paste when water gets into it... I was going to use pwr steering fluid but motor oil is cheaper and easier to find in any gas station if you need it. Merc suggests it too so it made sense to me

    Make sure you purge your cylinders too..... I took the hoses loose at the transom and took the cylinders loose from the drive so I could work them back and forth by hand to clear the atf.... Then extend one all the way and stick the retract hose in clean oil. Push the cylinder in to suck in new oil Give it some time to pull the oil in or it will suck air when you pull the hose out. Repeat with the other cylinder and put it together.... should self bleed with a few cycles after that.

    But, where are the reevets?
    1981 Wellcraft V-20 CC Fisherman (FREE BOAT)
    1989 Wellcraft Monte Carlo 28(Build thread here)
    1992 Hotsports Jet'n'Cat Yam 701 WR3 drivetrain "SS George Washington"
    90's Yamaha WRIII and a pair of 95 Kawasaki ZXI-900's
    Fresh clean cheap oil is better then old dirty expensive oil any day


    • #3
      Re: power trim fluid question: motor oil or hydraulic fluid?

      You don't mention what year motor you have but from your description I can assume a late '70s or early '80s model with the pump/reservoir in the boat.

      Those early systems did specify SAE 30 motor oil BUT, it is perfectly OK to use automatic transmission fluid in them as well. Many of the systems out there, including mine, use the ATF without issue.

      Whichever oil you choose, don't mix the two. Be sure to purge the entire system, including lines and cylinders.


      • #4
        Re: power trim fluid question: motor oil or hydraulic fluid?

        yes... its an earlier 70's model...

        i have not been using atf but hydrolic fluid...
        i think i will make the switch to 10w40


        • #5
          Re: power trim fluid question: motor oil or hydraulic fluid?

          My 1997 Mercruiser used 10w-30.