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I read somewhere that if you change an oil and filter and check the level using the dipstick this will not show the correct level because once you start the car, the oil will move into the filter area, then when you switch the car off and the oil travels back, the dipstick level is now lower because some of the oil went to the filter area. Therefore you should change oil and filter, add oil, switch car on then off, allow to drain back then add oil again as needed.

Is this correct and if so how much of a difference would it make on on the dipstick i.e. is it a lot of oil that goes there?

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    If you fill with the correct amount of oil (as specified in the handbook) you don't need to check the level at all. In any case, the amount of oil in the filter is probably less than the difference between the MAX and MIN marks on the dipstick.
    – alephzero
    Commented Oct 17, 2018 at 21:41
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    @alephzero I had an external filter on mine - held a litre, mounted vertical so no loss when changing...
    – Solar Mike
    Commented Oct 18, 2018 at 5:15
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    @alephzero Except there's always some left in the system, so you normally need to add less than the amount specified...
    – Nick C ♦
    Commented Oct 18, 2018 at 8:11
  • Oil level differs due to cold vs hot, engine ran recently vs not.
    – agent provocateur
    Commented Oct 19, 2018 at 19:20

5 Answers 5

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Check the oil in the method shown in the specific manual for the car you have.

If not other information is available for your vehicle, checking oil is best done when the car is cold, standing on level ground. If that isn't possible, at least leave the oil to settle for a few minutes before trying to read the dipstick.

On a dipstick, the difference between low and high is normally 1qt. Oil filters would hold a lot less than that, so any difference would be negligible.

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I usually do both. Fill it, checking regularly as I go. Wait a couple of minutes for it to settle (usually the time taken to put the tools away), check again. Start the car, drive it round the block to make sure it's all ok. Park up, leave it overnight, check it again the next morning.

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The method I used to use to ensure I has the dipstick level on max after an oil and filter change is as you describe; top up oil using oil filler cap to MAX on dipstick (being sure to allow a couple of minutes for oil to find it's way to the sump). Start the engine and allow it to run for a short time. Switch it off and leave it for a short time, re-dip the sump and add oil to bring the level back to the max marker on the dipstick. This method I've always found perfectly acceptable. I've never seen the oil light stay lit once the engine is started the first time.

That said, I was servicing a car with a spin-on type oil filter with a friend of mine some years ago. My friend works on all kinds of vehicles including military and pre-war. Prior to handing me the filter to refit, he filled it with a small amount of new engine oil. When quizzed on this, he told me that oil is drawn from the sump into the filter prior to being supplied to the engine and filling the filter first means you avoid the few seconds at initial startup when the pump if simply filling the empty filter.

It's important to refit the sump plug prior to attaching an oil filter full of clean oil though. Whilst most genuine oil filters will have a non-return valve, there is scope for a small amount of clean oil to escape during this operation and you don't want that to escape onto the floor.

Also, even with this method you need to start the engine and stop it again to check the true oil level prior to considering the job complete.

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I've found the amount the oil level goes down after running the engine for just a few seconds is significant. Now I always run the engine for just a little bit to let the filter fill up, then top off the oil after waiting a minute for it to settle.

It's not just the filter capacity. There is oil backed up inside the engine that drains out as well. I'm sure you've noticed that as soon as you break the filter free a fair amount of oil comes out and goes everywhere.

I don't think it's a good idea to pour in what the spec says and assume the level is correct. Always check the level. Mistakes happen. I've changed fluids a million times, but once while changing transmission fluid on my Acura (requires multiple drain/fills with driving in between) I just got into the groove and spaced out on the last drain/fill and forgot to drain first. Always verify your work.

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You should check your owners manual to find out how to check the oil. Otherwise I would recommend filling it up, letting the car run for a couple of minutes, then let it sit for a couple and then check the dipstick. Make sure the car is on a level surface aswell.

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