Okay to add new oil to old?

Question

Title pretty much explains,

I change my oil every 4-6k miles depending on how generous I’m feeling, however will the oil dirty oil that’s already in the sump mix with the clean oil when topping up?

Normally I just top up but in this case I have had to drain about half a litre out on two occasions

First when I changed the oil as I overfilled

Second when topping up (overfilled again after 3k miles)

so it's had quite a bit of new oil mixed with the original stuff, just wondering will the new stuff mix fine with the old, if not I’m going do an early change and try not to be such a dope when topping up.

Answer 1

Mixing new with the old will cause you absolutely no issues. As long as you are using the same weight oil, it will mix up and you'd never know it. Continue to change your oil at the specified interval and you should be golden.

Answer 2

Usually when changing the oil you won't be able to fully drain the old oil anyways and the old and new oils will mix, like it or not. Usually this is not a problem even if the weights are different, though it's safer to stick with the same brand, as some argue the components in the oil being incompatible may cause issues.

What you should be wary of is mixing synthetic oil with mineral oil, it i said that this causes problems more often.

Answer 3

Mixing old with new won't hurt anything. If your engine is consuming too much oil, for instance, you would need to add new oil more frequently because you need the right oil level all the time. I have got cars that needed as much as 1L of new oil every 1 or 2 weeks because the oil piston rings where kaput. Nothing happened except $ going down there as frequently as not eager to :)