Can you mix engine oils?

paperclap

Hi all,

Not sure if this is the right place to post this, but couldn’t see a “motoring” category.

I need to top up my oil by 100ml-200ml or so. It’s a Honda Civic, and takes fully synthetic 0W-30.

Not got any, and don’t really fancy buying any unless I really have to (as wanting to probably change the oil and filter) next year at some point.

But, do have some semi-synthetic 10W-40 from the previous car.

Is it okay to mix these oils?

Some people say “Yeah, been doing it for years”, others say “No, not recommended”.

What is the actual truth?!

Bookworm105

actual truth is you can do what you want

obviously the manufacturer intended the car to perform best with the specified oil, nonetheless the old adage always applies: it is better to have enough oil, than low oil.

running such a small mix as you mention until ready for the full next change is not going to damage your engine.

400ixl

For the sake of £10, no do not mix them.

Your oil is likely a fully synthetic oil not semi. It also reacts differently at both cold start and when warm. Whilst it won't make your engine explode, it is really not advised and can lead to additional wear.

Just get 1 litre of 0w30 fully synth oil and top it up to where it needs to be.

Ectophile

There is a motoring section https://forums.moneysavingexpert.com/categories/motoring.  You must have missed it.  But if you do post there, expect a lot of snide comments.

For a little topping up, it hardly matters.  Oil is oil.  10W-40 is a bit thicker than 0W-30.  But you only need a small amount.

If you can find the car's handbook, there's usually a chart showing which oils are best for different temperature ranges.

fatbelly

Engine oil does a lot of work in an engine. It's not something to mess around with and 1 litre of the proper stuff isn't going to break the bank

https://www.opieoils.co.uk/c-652-0w30-engine-oil.aspx?sort-by=1&entityids=31

Baldytyke88

paperclap said:

But, do have some semi-synthetic 10W-40 from the previous car.

Better to have any type of 0-30 but it would be ok if you are desperate.

onomatopoeia99

To top up, yes, adding a little semi-synthetic isn't going to do any harm, ditto mineral, you can mix most engine oils for the purposes of topping up.  Only caveat is absolutely do not mix any castor based oil at all with mineral or synthetic oil. types (most people won't ever own a vehicle that uses castor based oils though so you're unlikely to have any in the garage. Unlike me).

paperclap

Hi all,

I’ve taken a look through my car’s manual. While it does seem to mention that the car accepts a wide range of viscosities, it doesn’t appear to mention “mineral”, “semi-synthetic” or “synthetic”.

This does make me wonder whether you could in fact fill the entire sump with semi-synthetic? 

400ixl

Yes, you can use different oil viscosities depending on the temperatures throughout the year for where you live, be it a cold climate, moderate or hot.

What you shouldn't do is mix oils at the same time. Tolerances are very fine on modern engines and putting in anything like in the 1980's is long gone.

Just spend a tenner and put the right oil into to. If it takes a litre (which is where many cars have the oil light come on) can be nearly 1/4 of the total amount on many 1.4/1.8 engines.