True cost of not maintaining your car

5. Replacing PCV valve regularly 

The positive crankcase ventilation, or PCV, system helps regulate the flow of fumes around the engine. It includes hoses as well as a PCV valve, which should be replaced at recommended intervals.

"The PCV valve helps protect the seals and gaskets on an engine. It keeps them from getting corroded and cracked, which can cause oil to leak," says Currin. "The cost for a replacement PCV valve is just a few dollars, plus a minimal cost of labor to install it. But if you don't get it replaced when necessary, the seals could leak.

"If you do have a leak, it costs over a hundred bucks to replace a valve cover gasket. If it gets really bad and the head gasket starts to leak, you could be faced with thousands of dollars for repair bills."

Cost of skipping: Leaking head gasket, failed emissions test.

6. Changing spark plugs and filters 

Do you live in a state that requires your car to pass an emissions test? If so, failing to maintain your car could lead to a huge repair bill to bring the vehicle into compliance.

"The average repair bill is somewhere between $335 to $350 to fix a problem that causes an emissions test to fail," says Rich Parlontieri, chief executive officer of Speedemissions, a vehicle emissions testing/safety inspection company with stations in Salt Lake City, Houston and Atlanta. "Common causes of failed emissions tests include faulty oxygen sensors, air flow monitors and catalytic converters."

States may require drivers to pay well over $700 to attempt to fix their own cars before the state finally grants them a waiver to bypass the emissions test, Parlontieri says. Basic maintenance can prevent many of these problems from occurring in the first place.

"The best way to improve the odds of passing an emissions test is to maintain your vehicle. A well-maintained engine is usually a clean engine as far as emissions are concerned," says Parlontieri.

Basic maintenance includes changing the spark plugs, air filter, fuel filter, PCV valve and oil regularly, Parlontieri says. Checking ignition timing and adjusting the carburetor (if you have an older vehicle) can reduce emissions and greatly improve the odds of passing an emissions check.

"It's amazing what following the maintenance schedule in the owner's manual can do for a car when it comes time to take the test," says Parlontieri.

Bad emissions also involve an environmental cost that we pay in the air we breathe.

"When you fail a test, it means your car is creating a lot of pollution," says Parlontieri.

Cost of skipping: Damaged catalytic converter, failed emissions test.