I got mad at my boyfriend and poured urine in his oil reserve and in his gas tank. What will happen to his car?

Probably nothing too terrible will happen to his car, but I would advise you to tell him what you did so that he can change the oil and add dry gas to the gas tank. On the other hand, bad karma will likely follow you for the rest of your life if you do not tell him.

Your actions won’t be terribly effective.
You need to go back with a sledgehammer and
do a better job.

Oil reserve? Is your boyfriend a small nation?

Don’t do that again, the car is innocent. Next time, just give him a lariat in full swing.