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I previously did an oil change at a garage and I noticed they add the oil then switch the engine on let the oil go down and then add more oil befor switching it off and letting new oil come back

However surely this is the incorrrect way of doing it. When you switch the engine on the oil goes into the engine parts and when you switch it off it returns to the dipstick level after a few minutes where it should return to where it was before you switched the engine on.

In this case the oil was a bit over the dipstick level but they told me not to worry.

However am I correct in saying you fill it up with the engine off up to max and that’s it then you switch it on. In worst case I imagine only after switching it off for a few minutes can you check the level again as the oil has returned the you add if needed.

Like I say it was a bit over max which could have been avoided and I have noticed more than 1 garage do this. In one case my friends car oil was well over max.

So are these guys doing it wrong or is there some correctness/wisdom behind this?

Thanks

Are they doing

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  • Don't think what you say you saw you actually saw. They turn the engine off, then wait and then check the level.
    – Solar Mike
    Oct 28, 2020 at 16:27

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Generally with an oil change you also change the filter. On most engines the filter holds a significant amount of oil and it will not fill up until the engine runs and pumps enough oil into it.

If you check the oil level before running the engine for a minute or so, you may leave the oil level low since you checked the level with the filter and also other internal parts empty. So it's a common practice to initially fill the engine up to at least the indicated "full" level (perhaps a bit more but, in order to not overfill, the mechanic performing the oil change will generally knowingly leave the engine slightly short of the ultimate full level), start the engine to circulate the oil and get everything "filled up". Then after shutting off the engine a check after a few minutes will let you fill to the proper level more accurately.

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  • Can you elaborate on the "leave it about 1 qt. short" logic? Why not just fill it to the safe level, turn it on, let circulate, turn it off, and then top it off? By leaving it purposefully 1 qt. short then you are practically guaranteeing yourself issues if you forget to top it off.
    – MonkeyZeus
    Oct 28, 2020 at 19:38
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    I've never seen/heard of leaving the oil 1qt (or liter for the rest of the world) shy before starting the engine after an oil change. I don't think you're going to cause any issues doing it, however, normal protocol calls for putting the oil in to the top mark on the dipstick, running the engine for a few minutes, shut it off for a few minutes, rechecking the oil and topping as needed.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 28, 2020 at 21:22
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    "Short" probably means "short of the final full level". Not intentionally low on the dipstick.
    – D. SM
    Oct 29, 2020 at 0:42
  • If you have a proper service manual, you know exactly how much oil to add after draining the engine without any messing about as described by the OP. Running the engine after refilling is done to check for leaks, and checking the dipstick level is just a final check.
    – alephzero
    Oct 29, 2020 at 2:10
  • The manuals I've seen give the full system capacity, not the amount of oil needed given that some oil remains in the engine. Also, sometimes the amount is not easily measurable (my car needs about 3.6 quarts for example).
    – D. SM
    Oct 29, 2020 at 15:21

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