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Flushing out the crankcase

Discussion in 'Mechanic and Repair' started by lawn6@bigpond, Aug 18, 2005.

  1. lawn6@bigpond

    lawn6@bigpond LawnSite Member
    Posts: 61

    When should this be done and why , I have an old engine that been working for long periods and been told I should give it a flushout .
  2. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    If the engine has had regular oil changes and the oil stays fairly clean I wouldn't worry about a flush. If the engine has been run hard and neglected in oil changes it wouldn't hurt to flush it out with clean mineral spirits to remove sludge deposits from the oil sump. I just done a 6 mo. old Kawasaki 3" trash pump, The dummys had never changed the oil in and it runs all day every day at a dairy.
  3. MBDiagMan

    MBDiagMan LawnSite Senior Member
    Posts: 852

    I think that restrob is sharing some valuable wisdom with you. Mineral spirits makes a very good and affordable flush.


    In years past I have seen, and even done it myself, run an engine for a few seconds with kerosene in the crankcase. This was in the days before we had the fabulous oils that we have these days. I have since quit that practice.

    Some people still believe that this is okay to do. If you insist on running the engine with solvent in the crankcase, make sure that there is also oil in it.

    My preferable flush if using mineral spirits is to get the engine to operating temp, drain the oil, put the drain plug back in, fill with mineral spirits or whatever flush you are using and then immediately pull the plug again.

    Another approach would be to put half and half oil and solvent and run it for a few seconds then drain. Always do this while engine is at operating temperature for best effect.

    All that said, my personal preference would be to change oil and filter (again draining while engine is at operating temperature) and filling the engine with a CI4 grade oil such as Mobil Delvac, Chevron Delo or Shell Rotella and then run the engine in normal operation a few hours and change. Continue to do this until the oil stays clean for several minutes after an oil change. Always drain the engine hot so that the contaminants are churned up in the oil.

    Good luck,
  4. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    I use kerosene myself, guess that is a mineral spirit?

    Run the engine until it reaches normal op.temp and shut if off.
    Add about 1/4th of the crankcase capacity (so a 4-qt. engine takes 1 qt. keros, a 2-qt. motor takes a pint, etc).
    Then start the engine and let it idle 5-8 minutes, then shut it off again and change the oil IMMEDIATELY.
  5. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Posts: 2,613

    Wow, 5-8 minutes...I am not sure you gain much by going over a minutue on a flush.
  6. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    I didn't explain fully, But I did in fact warm the engine up. Then drained the old oil, Reinstalled the plug and filled it to the full mark with the mineral sprits.
    Pulled the spark plug and spun it over about 12 to 15 times to splash it around then drained it and blew it out with air. Put a small piece of shop rag on the end of a coat hanger wire and ran it in the drain hole and it came out clean. Reinstalled the plug and refilled with oil and sent it out.
    I will NOT start a engine with ANYTHING but oil in it, Nor will I suggest to ANYBODY else to do so.
  7. MBDiagMan

    MBDiagMan LawnSite Senior Member
    Posts: 852


    I like that method.

    Have a great day,
  8. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    Thanks ! I just don't like taking chances with already neglected engines, It would be my luck the thing would blow.

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