Want this question answered?
why would you want to? Yes you could, the viscosity will average out .
Yes, as long as the ambient temperature is above fifty degrees.
Yes
Yes, you can mix weights but use exactly what the manufacture recommends and do not mix weights.
Yes of course you can mix them what what would be the reason to do so.
not recommended
There should be no problem with mixing them.
No worries. If 10w30 was suited for your current climate then your new mixture will do just fine. If you needed to use 5w30 because the temps are still below zero in your area, then you may want to change to entirely 5w30. I remember hearing about people with LS1's in their Camaros mixing 4 qts of Mobil 1 10w30 and 2 qts of 15w50 in order to achieve a mix that was similar to a 10w40.
Yes you can. I spoke to Castrol customer service on 16 Feb 12 and asked if I could mix a left over 1 gallon bottle of the older Syntec with the newer Edge formula I just purchased. I was told as long as they are the same viscosity, they can be mixed.
This is from Castrols customer service after I emailed them this same question... Our previous Castrol SYNTEC product has been improved, renamed and repackaged as Castrol EDGE with Syntec Power Technology (SPT) however it remains in a black bottle and is fully compatible for use with the previous Castrol SYNTEC product so as always, you can use the same SAE grade of either product together for 'topping off' purposes without fear. The new Castrol EDGE with SPT is not only as good as the previous Castrol SYNTEC product that you were using but better!
Nothing if they were approved oils. You can mix 10w30 with 5w20 etc. Not a good idea but you can do it. You can mix brands with no problem.
It could cause engine damage. We had somebody put 10W40 4 stroke oil in the injection oil tank of a 2 stroke sea doo pwc and it ran for less than an hour before there was significant engine damage. He is now forever known as Captain 10W40.