Mixing oils

Honest John Back Room » Technical matters
View Threaded
Wed 16 May 2007 13:31
Mixing oils - csgmart
I am due to change the oil in my car soon. I have 2 part used 5l cans of oil (same spec and brand) which total up to 4 litres. I need 4.5 litres for the change so I have purchased some additional oil to the same spec as the oil I already have, but from another maker.

Question is - is it OK to fill up the car using the 2 different brands? Like I said the oil spec (10W-40 - I believe) is the same for both.

What else do I need to check on the label (if anything)?
Reply | Report as offensive | Link
Wed 16 May 2007 13:38
Mixing oils - yorkiebar
You need to check the types (mineral, semi synthetic or synthetic. Also the quality type SL/CF etc or AB/ etc.

But if you had car serviced and it needed topping up would you know exactly what was in it ? My point is that they will mix, but any mixture will result in the oil being of the lowest quality of the mixes used !

Try to stick to same oils if possible, you seem to be trying to do so.
Reply | Report as offensive | Link
Wed 16 May 2007 13:47
Mixing oils - mss1tw
Regularly do this on the bike.

Car takes most of a bottle which is then kept for any top ups needed, any dregs are used in the hext oil change.

If they are both the same type and viscosity I wouldn't worry.
Reply | Report as offensive | Link
Wed 16 May 2007 15:19
Mixing oils - Hamsafar
It isn't best practice and would never be recommended or endorsed, but they are supposed to be able to mix with each other.
Reply | Report as offensive | Link
Wed 16 May 2007 16:22
Mixing oils - Number_Cruncher
>>is it OK to fill up the car using the 2 different brands?

It isn't something I would ever lose sleep over.

Number_Cruncher
Reply | Report as offensive | Link
Wed 16 May 2007 16:27
Mixing oils - bathtub tom
>>is it OK to fill up the car using the 2 different brands?

It's quite likely they're from the same source.
Reply | Report as offensive | Link
Thu 17 May 2007 12:48
Mixing oils - GregSwain
It isn't something I would ever lose sleep over.


Nor me, but common sense doesn't always prevail in the Backroom. I buy the cheapest 10w40 semi-synthetic for changes, and the absolute cheapest mineral rubbish for top-ups. Oil deteriorates during the 12 months it's inside your engine, so if you wanted to be REALLY pedantic, you could argue that topping up 6-month-old oil with identical brand-new oil equates to mixing oils with slightly different characteristics!!

Or you could just do what everyone else does, and stop worrying about it. Buy the cheapest semi-synth oil which meets the manufacturer's spec. In my experience, even the very cheapest semi-synth oil on the market far exceeds most manufacturer's minimum specs.

Would you mix Esso petrol with Texaco petrol? ;-)
Reply | Report as offensive | Link
Thu 17 May 2007 12:52
Mixing oils - csgmart
Thanks - I just wanted to check if there were any obvious thing to look for before doing it.

I think both are synthetic.

One is from Quantum - Synta, the other is from Fuchs (don't have the can here right now but it's a 10W-40 oil).
Reply | Report as offensive | Link
Thu 17 May 2007 14:38
Mixing oils - MW
No problem. The mixture will just be an average of the two qualities you use.
Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide