Is it safe to combine different oils of the same grade?

For example: if my motor had Titan GT1 5W/30 in it and for top-up I use, let's say Castrol 5W/30 - would this be OK? Just wondering because I have
some spare oil of the same grade and don't want to go out and buy more oil unless I really have to.
FWIW, both oils are classed as BMW long life oils.
Thanks.
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It depends on what additives are in the individual oils, most oil company experts will tell you not to mix modern oils (they would though).
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"Depresion" <127.0.0.1> wrote:

I'd be worried if oils couldnt be combined since you never completely remove the last lot when you change!
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This was, in fact, the problem with the first generation Mobil 1 oil. You could fill your crankcase with it and the little bit of old petroleum oil behind wasn't much of a problem, but if you decided to convert back to petroleum, having a little bit of Mobil 1 left in the system caused trouble unless you flushed it all out.
This problem was fixed many years ago and you can now mix the olefin synthetics with ordinary paraffin oils. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Yes. That's part of the SAE specification. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Perfectly OK, I have done that for years. Oil is oil and there is no real difference between Halfords and Honda oil that conforms to the same specification apart from 12/litre.
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It's OK to mix oils as long as they meet or exceed the manufacturers specifications, usually found in the owners handbook. For example SAE, ACEA, API, etc.

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