For most us, we would quickly answer ONE, the air filter. Some might think a bit longer and respond w/TWO, the air filter AND the oil filter.
Did you know that many vehicles have four or more filters? All that need changing periodically AND some that require special tool OR that are hidden?
Most newer vehicles have TWO air filters. The one we recall in the engine compartment AND the one conveniently hidden, often behind the glovebox, the cabin air filter.
Having an old engine air filter can reduce engine power, increase engine wear and decrease throttle response when you push on the gas pedal. Fresh air coming in to gets optimum combustion. That combustion explosion is what makes the car go. Not changing it would be like trying to run with a clogged up nose and duct tape over your mouth.
Often forgotten, when a dirty cabin air filter is shown to customers they are surprised to learn they’ve been breathing that air when they drive. Most newer vehicles will have at least one cabin air filter.
Then, yes there is the oil filter that requires a weird wrench to get off. Most of us routinely change this one when we have our oil changed… You’re doing that, right?
So what are the others?
Another common one is the gas filter, which traps sediment such as dirt and rust particles from getting into the fuel pump, carburetor or fuel injectors. It should be replaced every 20,000 to 35,000 miles.
Most newer vehicles don’t have one, but if yours is older, you might also have a transmission filter. If yours does, changing your transmission filter every 30,000 miles will greatly increase its performance and longevity and cut down on noise and shifting problems.