Originally Posted by blupupher
Mix away, all oil are compatible with each other, you are not going to ruin an engine mixing, but not going to make it last longer either.
Just be aware that your viscosity will not be precise if mixing weights, but since your just mixing 5w-30 of different brands, not an issue.
Compatible is simply that they mix, can be cooled to the combined freeze point, and then heated to 150C, and then cooled back to the freeze point with 7 reference oils, and they don't split like salad dressing or blow chunks of precipitate.
That's ALL that the compatibility test offers.
It doesn't offer that any two 5W30s when mixed will be a 5W30 (in partiular the 5W part), nor that a 0W20 and 0W40 will have a 0W at the start of it. In fact, all off the serious failures (and there have been a few), it was the "W" end of the spectrum that failed, in the Toyota factory fill case, with an incompatible service fill, the "W" grade became so bad that the engines couldn't pump the oil at any sort of reasonable temperature.
Extremely rare, and in a warm climate, seriously unlikely to cause any issue.
But if you are in 0W country, and you NEED 0W, the Myagi defence applies...best defence is no be there.