Calling all the oil experts!

[pyemaster]

Right, so let's say theoretically someone just bought his wife a cheap little Civic to get her around, and that they changed the oil (5w30 fully synth) and filter shortly afterwards just as a matter of course, and that they theoretically then consolidated the remaining 1.5l of oil into another part-filled bottle of 5w30 fully synth oil I may have theoretically had kicking about to save space, before theoretically realising that that bottle was in fact 5w30 SEMI synth.

Now, theoretically of course, seeing as they're both 5w30 and of the same brand (Carlube), is this an issue?

The Internet is awash with strong views on both sides, from 'totally harmless to use a mixture, you'll just not see the benefit of using fully synth by itself', to 'this will destroy your bottom end immediately, throw the mixture out straight away and just get more fully synth'.

So, er, theoretically, what are the chances of risk? It's only 3l of mixed 5w30, but if I don't need to dispose of it, I'd theoretically rather not.

Yours theoretically,
Owen

 

[MarkW]

for a cheap run around, I'd keep it for topping up. Putting a small volume of the blend in to maintain level isn't going to cause much harm.

Of course the internet is full of "experts" who'll have their view

 

[Towpack]

Theoretically it's a no no, realistically I'd use it without worry.
If you change from SSynth to fully Synth there'll be a mixing of both anyway.

 

[clivehorridge]

Ive always been confused by the difference between fully synth and so-called semi synth.

I say so-called, because semi implies 50/50, yet when I read the bumf on the bottle of the so-called semi synth in my 80, it says “part synthetic”....

What does that mean, which part?

So I’ve given up worrying about it, my service garage puts in what they think is best, so-called semi synth, named brand, correct viscosity, WTF...

JMHO (theoretically)...

 

[frank rabbets]

https://en.wikipedia.org/wiki/Motor_oilhttps://en.wikipedia.org/wiki/Motor_oil

Not much a fan of wiki but the above looks like your answer. I would have thought mixing same API would be OK.

 

[pyemaster]

Cheers fellas

Owen