Mixing fully synthetic oil with semi synthetic

[Steve M]

I currently have Millers fully synthetic 10w 40 engine oil in my Zetec

Checked the oil earlier & it needs topping up before my next drive, millers fully synthetic not available locally

Am I ok to top up ( probably 0.5 litre ) with a good quality semi synthetic 10w 40 oil ? Or is it wise to order the fully synthetic millers as a top up ?

Cheers

Steve

[Kit Car Electronics and Essex AO]

I'd drain it and refill with the correct 5W30...

[Steve M]

[Kit Car Electronics and Essex AO]

I'm sure you'll be OK topping up with semi...

[AdamR]

No probs to mix    5w40 or 10w40 is a good shout for cars driven a bit harder than Mrs. Smith's shopping Mondeo The high number is the viscosity when up to temperature, so it will hold the same pressure at a higher temperature (eg. driven frequently at high revs, on track, etc) than the manufacturer recommended 5w30 oil.

[corsechris]

True enough, Alfa specify 5W/30 for the V6 or 10W/60 for 'heavy duty use in moderate climates'  Conversely, put anything other than 5W/20 in my Jeep and the engine management b***hes about it.

[Kezman]

Your right to ask the question. I think strictly buy the book it's only adding the exact same oil that you've got in......but as you point out, if your in a situation where you can't get you hands on some easy, I would imagine putting in a 'top up' of semi in reality is not going to cause any issues. Better that then not enough in eh? It often says on oil containers can be intermixed but then goes goes on to kind of say best not to......Go figure. Their looking after their sales I suppose..

As you've hinted your going to, I would certainly keep things as equal as you can and put the same viscosity though....(10/40)