By mistake I substituted Mobile 1, 5w-20 synthetic motor oil for Mobile 1, 5w-30 synthetic motor oil which I usually use. I faithfully change oil & filter at 5000 mile intervals. Will I do engine damage by leaving the 5w-20 in engine until next oil change?

 

Without looking, pretty sure that engine calls for 5W-20 anyways??? Perhaps check the owners manual? If it calls for 5W-20, then you can use it indefinitely, if it calls for 5W-30, however, it may be a good idea to exchange for the proper weight...