A few years ago I bought engine booster (goes in the gas tank) and a quart of oil for my car.
Poured the boost in the engine.
I immediately stopped what I was doing and had my car towed to a mechanic. He told me that it probably made things run smoother. (But proceed to change the oil for me anyway.)
dumb dumb dumb...
My daughter once added a quart of oil to the radiator in our B-210 thinking that’s where you put the oil. A week later I checked fluid levels and thought the engine must be shot because there was oil in the water. Daughter saw what I was doing and said “oh is that the water cap?” We got it straightened out but I despaired of her learning anything about that sort of thing and she got strict orders to call Dad whenever anything needed doing on the car. Later she was all-time valedictorian at her small college and went on to a very successful career with an MBA but she never could figure out cars beyond simply driving them.