Over time and miles, your car might start to slow down. It might not accelerate as quickly as it once did; the engine may not run as smoothly as you remember, or the fuel economy may dip—but ...

If you're the type that loves to keep a clean car, chances are you've popped the hood and given your engine a thorough scrubbing. From degreasing to gingerly rinsing it with a hose and scrubbing it ...