My engine oil is kind of black and running low. I know its ok for old and new oils to mix, but is there a reason why on some occasions you should top up and on others you should drain?

Also I dont know what they put in last time e.g. synthetic or not and type of oil. But I understand no oil gets fully drained so it shouldn't matter if whatever oils mix?

  • I'd stick to the manufacturer recommended interval, oil type, and weight. Read it off the manual, the website or the oil cap if you need to. Change it now if it looks sludgy, and go from there.
    – geoO
    May 23 '18 at 15:20
  • "My engine oil is kind of black and running low" Change the oil and filter!
    – Moab
    May 23 '18 at 20:08

You should drain it if it's time to change it, and top up otherwise.


If you don't know when it was last changed, change it - and the filter. That way you know where you are.

If it is getting low - why? Is there a leak, or is it being burned off? How quickly is it going down? If there is a loss, you need to know why, and may need to deal with it before it gets more serious...

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