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I had my BMW M52 engine completely rebuilt. The rebuilder retired and I’m not sure what’s the break-in procedure or what oil I should be using?

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  • I am guessing like stock oil, I mean, if it normally takes 5w40 or 10w40, I would use it, if you understand me...
    – Eziooh
    Apr 26, 2019 at 10:32
  • Has the engine been run? If not, throw some BreakIn Oil in, run for about 50 miles, then drain and switch to the correct oil for that engine and follow Solar Mike's break-in instructions.
    – PeteCon
    Apr 26, 2019 at 16:20

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When running a "new" or rebuilt engine for the first time after I had built it from scratch I would use it gently for 200 miles - not exceeding 2500 rpm approx or putting it under heavy load. Then over the next 500 miles I would increase the rpm occasionally to 3500 or 4000. After 1000 miles Then it was fine.

As for oil, I would use the manufacturer's specification and often better. On a re-built engine I would do the first change at 500 miles (oil & filter) and then follow normal change intervals.

If the engine has not been started before, I would remove the spark plugs and spin the engine over on the starter until the oil pressure had built up and there was evidence that it had come through the rockers or valve train (sometimes can be seen by removing the filler cap).

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  • Why do people say not to use synthetic oil on a rebuilt engine? and only to use regular oil as it helps “sit” the rings better? is it a myth? synthetic oils are superior in their properties so why would one use regular oil?
    – Tom
    Apr 30, 2019 at 8:04
  • @Tom perhaps so that the engine can "bed in" properly - but new engines come with fully synthetic so perhaps it is a myth...
    – Solar Mike
    Apr 30, 2019 at 8:21

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