The liquid is not a fuel. Which throws the ratio of A:F off. Which can cause the car to run lean and foul out the plugs. Of course if you let it trickle into the vehicle at a steady stream you'll more than likely be okay. I've seen people use a very generous amount of a seafoam type cleaner on their vehicles and it causes it to bog out and die. Also it may or may not throw a check engine light to cause random misfires. It's just what I've seen from people doing it. I'm sure there are benefits to using it. I would personally stay away from the product as far as that goes.