Umm the gas tank! NO! It is fine to add some to your oil. It will act as a detergent cleaning valve deposits etc. I wouldn't run it long before doing an oil change.

-'96 SE MTX 3L -'98 SVT 1,173 of 6,535 -'05 Mazda 6s, loaded, g/f's ride -Need a 96-00 manual on CD? PM or email me