Does it hurt anything to mix 10w30 with 5w30 or 10w40 oil?
Short answer, “probably not.”
Longer answer, “you should only use the oil specified in your vehicle’s owner’s manual.”
Question; are you a gambler?
You could be gambling with your vehicle’s engine by using the wrong oil.
Are you a gambler?
No, not at all as long as the weights are what your owner’s manual specifies or average out to be close to what is desired such as 10W plus 10w-40 to arrive at something close to 10w-30. I have been mixing weights and brands for years in an older vehicle but use weights specified in a newer vehicle still under warranty but would not be concerned about mixing brands. Presently I have three different brands in my older vehicle because I must use what I have stockpiled.
Brands must be compatible as you may need a quart during a trip and might need to use what is available. The military can not be fussy about oil brands either.
YES…When you mix multi-viscosity oils, it’s impossible to predict what the viscosity of the combined oil will be…If the 5w rating is important to you or your car, if you mix it with 10-40, chances are the 5w rating will be lost…Most cars will tolerate this blending but some cars are pretty fussy about the viscosity of the oil…
It depends.
If your car’s owner’s manual says you can use either 10W-30 or 5W-30, then yes, you can mix 10W-30 and 5W-30 and your engine will be fine. However, in this example, I would not mix in any 10W-40 oil. To do so would not be a good idea, although you would likely not notice the difference, other than experiencing slightly higher fuel consumption.
It all depends on what kind of car you are talking about, and its oil needs.
Things can’t get too far out of hand if you stick with similar grades of multi-viscosity oil…But if you add straight-weight oil into the mix, the resulting viscosity will get thick fast…
Remember this. The actual base oil in multi-viscosity oils is always thinner than the thinnest grade on the label… So with 5w-30, the base-stock oil is thinner than 5-weight oil…The additive package then dopes the oil to act like 5w when cold and 30 weight when hot…Quite a trick…
Make sure that the oils you are using all meet or exceed the specs for your engine.
Thanks to all for the advice.