Mixing new engine oil with (un-used) existing engine oil

[SpeedBash]

Car is due its (long life) service next week.

Putting together a list of items I need to buy for the mechanic and have a question.

I have some un-used oil left over from the last service (2yrs ago) and wondered if I can mix this with the new oil I need to purchase.

As long as the new oil is of an identical specification as the old oil, can I do this?

If so, can I mix brands or should I stick to the same brand?

I suspect it is a case of yes in theory, but not advised in practice.



Apologies in advance if this is a noddy question.

[Blue Oval84]

If the oils are of the same spec then they can be mixed no problem at all

[FranKinFezza]

Both oils of the same grade should be fine.

[CraigyMc]

My TT has longlife servicing - usually needs doing about every 16,000 to 18,000 miles.

In the manual it says not only can you top up with the same sort of oil, you're actually allowed to add up to 1l of non-longlife oil if you must. They do recommend the longlife stuff though.

C

[SpeedBash]

Appreciate all the replies.

[I Love Lamp]

According to the chaps at OpieOils, even mixing the grades isn't a problem.

5w/40 and 10w/40 for example, not an issue.

Edited by I Love Lamp on Wednesday 26th January 12:12

[r11co]

I Love Lamp said:

5w/40 and 10w/40 for example, not an issue.

As long as you appreciate that you end up averaging out the overall grade of the mix depending on the amounts of each you combine.

For example - a 50:50 mix of 5w40 and 10w40 will give you something approaching 7.5w40 and a corresponding change in the acceptable temperature range for the engine it is used in.

To answer the OP - no it makes no difference. "Un-used" oil is the same thing as new oil. I've heard a few people mention shelf-life but this is hyperbole to get people to buy more oil - as long as it is stored in a sealed container it doesn't 'go off'.

Edited by r11co on Wednesday 26th January 12:38