Best of all, you just add them to your engine oil. All of these additives are helpful in some way, but there are enough to fill an entire aisle at your local auto parts store.

Used right, in the right engine, they can help. Used wrong, they're a waste of money or worse. If your engine is healthy and your oil is fresh, save the $15 for something useful. Like gas. Or tacos.

My Volkswagen, however, needs more like 1,200 ppm in the air-cooled 1600 with about 100,000 miles and no catalytic converter. Does your car need zinc additive, though?

That's why using an oil stop leak product is so tempting to a lot of drivers. For less than $20 in most cases, these products promise to fix the oil leak in your car and keep it running.

John Paul, AAA Northeast's Car Doctor, answers a question from a reader curious about using Marvel Mystery Oil. AP Photo/David Zalubowski Q. I perform routine maintenance on my family’s cars and ...

Cons: Expensive Best for: Longer engine life, lots of traffic driving, lots of big hills, vehicles that tow things, especially in really hot or cold climates. Blend, or synthetic blend motor oil ...

Summary Manufacturers recommend using high-mileage oil in vehicles with over 75,000 miles on them. Usually, they are blended semi-synthetic as this results in the best combination of qualities and ...

If you want your 1974 Maserati Bora to last, use the best oil additive you can find. Photo credit: David Traver Adolphus / AutoGuide.com. Most drivers know that regular oil changes are necessary ...