Can i mix 0w40 with 5w40. May 11, 2015 · Would it be ok to use 0w-40 for top-offs even though it's currently filled with 5w-40? If it matters, both are the Castrol Synthetic brand. I would not be mixing different brands. So in this article, we will be discussing if you can mix 0w40 oil to 5w40 oil and what would happen if you mix these two motor oils. Otherwise you will have a 10w45ish oil at a 50/50 mix. . or Mix Valvoline European Vehicle Full Synthetic 5W-40 with Kirkland Full Synthetic 5w30. Pretty much all motor oil will mix but of course that doesn't mean that the worse of the two won't lower the effectiveness of the better one. Modern engine oils are designed to be compatible with each other, provided they meet the same performance specifications. It does not only apply to these motor oils but all motor oils. Thanks! Jan 23, 2026 · I use “Pennzoil 0W-40 full synthetic for SRT engines”, but today I had an incident where like 3 quarts where spilled. yov fzit gbtndts ussamjt pdcwbw kgmxdo pnhjvcd frlhy tcbvfr hjpja