10w30 in place of 5w30

can i just use one weight motor oil in both cars even though one specs 5w30 and the other is 10w30

Depends…does the car that says 5w-30…say you CAN’T use 10w-30. Some do…some just recommend 5w-30

Agree with above post, but this is the wrong question to ask in December, unless you live in the Deep South or somewhere else warm. Most cars now recommend 5W30 for winter and optionally 10W30 for summer. If I lived in West Texas, I would use 10W30 in the summer and 5W30 in the winter. As Mike says, if the car DEMANDS only 5W30, due to tight clearances, use 5W30. If so, I would use synthetic in a very hot climate. Synthetic has the advantage of being OK the whole year if you only drive a little, and don’t want to change oil twice a year.

Read your owner’s manuals. The answers you seek are there.

www.carbibles.com also has a good oil primer. You may want to visit.

The owner manual is the place to go, especially if you still have a warranty.

Just out of curiosity it’d be nice to maybe know what kind of cars you have (engine size wouldn’t hurt either.) Also, what’s the advantage to you of doing this, or are you maybe trying to settle an argument? I own a '96 Chrysler Cirrus and got a bulletin from Chrysler saying 5w30 is made from a better grade of crude than 10w30. Not sure if they were referring to Mopar motor oil, which is made by God knows who; or petroleum based oil in general. Why couldn’t you just use the specified oil? Have oil leak?

I just want to keep one grade of oil on hand for both cars 99 chevy monte carlo 3.8L and 00 chevy astro 4.3L. not to mention that everyone else in the family comes over to change oil here because i have everything needed.jb