Of course you can but when you do you are changing the viscosity of the oil. Your engine requires a certain weight or viscosity of oil. Use only the weight oil recommended by the manufacture.
Yes, just make sure the weights are the same so it will be compatible with your vehicle.
Different applications and engines require different weights of oil to operate properly and prevent engine wear. Therefore different weights of oil are produced.
Yes you can mix different brands but I recommend you do not mix different weights. You can even mix synthetic oil with conventional oil. But as the weight of the oil is critical, do not ever mix one weight of oil with another, no matter if it is synthetic or conventional oil.
Yes but it is not the ideal application; I have mixed oil weights in motors with no problems.
Because the oil will have a different viscosity than either oil, and they might not combine correctly. It may work okay, or it might not. If the oil doesn't work right, it may burn, smoke, or damage the engine.
Yes, you can mix conventional oil with synthetic oil with no problem.
Yes
As long as it is the same grade of motor oil the brand name should not matter.
It is a gas/oil mix motor, you don't change the oil.
You should never MIX different weights of oil. The above answer is correct, but if you find yourself in one of those unavoidable situations where you have no choice, go ahead and mix whatever you have to. It's better for the crankcase to be full than to have exactly the right oil in it. If it really grabs at your conscience, change the oil and filter as soon as you can.
Nothing happens, they just mix. You can buy "blended" motor oil.
Motor oil is insoluble in water and it is denser in water. Therefore, motor oil will not mix with water. It will remain separate.