Cars make us irrational. We call them our babies and lovingly wax them every Saturday -- or we turn up the radio to drown out the sound of a dragging muffler. Either mindset will cost you money, sometimes a lot of it.

Walking the line between obsession and neglect means you never spend a nickel without a good reason -- and good reasons can include spending money on something that’s not broken.

Here, then, are 20 ways you waste money on your car.

Premium gas instead of regular. Buy the cheapest gasoline that doesn’t make your car engine knock. All octane does is prevent knock; a grade higher than the maker of your car recommends is not a “treat.”

3,000-mile oil changes. Manufacturers typically suggest 5,000 miles, 7,500 miles or even longer intervals between oil changes (many car markers now include oil-life monitors that tell you when the oil is dirty -- sometimes as long as 15,000 miles.) There may be two recommendations for oil-change intervals: one for normal driving and one for hard use. If you live in a cold climate, take mostly very short trips, tow a trailer or have a high-revving, high-performance engine, use the more aggressive schedule. If you seldom drive your car, go by the calendar rather than your odometer. Twice a year changes are the minimum.

Taking false economies. Better to replace a timing belt on the manufacturer’s schedule than to have it break somewhere in western Nebraska. Better to pop for snow tires than to ride that low-profile rubber right into a tree.

Using the dealer’s maintenance schedule instead of the factory’s. Of course he thinks you should have a major tune-up every 30,000 miles. Most of the tasks that we generally think of under the heading of “tune-up” are now handled electronically. Stick to the manufacturer’s schedule unless your car is not running well. If your engine doesn't "miss" -- skip a beat or make other odd noises -- don’t change the spark plugs or wires until the manufacturer says so.

Using a dealer for major services. Independent shops almost always will do the same work much cheaper. Call around, owner’s manual in hand, to find out, mindful that the quality of the work is more of a question mark. Some dealers may tell you using outside garages violates the car’s warranty. This is a lie.

Using a dealer for oil changes. Dealers sometimes run dirt-cheap specials, but otherwise you’ll usually find changes cheaper elsewhere. If you’re using an independent shop for the first time, you might inconspicuously mark your old oil filter to make sure it has indeed been changed. And don’t let them talk you into new wiper blades, new air filters or high-priced synthetic oil, unless your car is one of the few high-performance machines built for it.

Not replacing your air filter and wiper blades yourself. Buy them on sale at a discount auto-parts store rather than having a garage or dealer replace them. Replacement is simple for either part, a 5-minute job. A good schedule for new air filters is every other oil change in a dusty climate; elsewhere at least once every 20,000 miles. Treat yourself to new wipers (it’s easiest to buy the whole blade, not the refill) once a year.

Going to any old repair shop. At the very least, make sure it’s ASE-certified (a good housekeeping seal of approval from the nonprofit National Institute for Automotive Service Excellence). From there, look for a well-kept shop with someone who’s willing to answer all your questions. Estimates must include a provision that no extra work will be done without your approval. Drive your car to make sure the problem is fixed before you pay. Pay with a credit card in case there’s a dispute later. Be courteous and pay attention. A good mechanic is hard to find.

Changing your antifreeze every winter. Change it only when a hydrometer suggests it will no longer withstand temperatures 30 degrees below the coldest your area sees in winter. Your dealer or oil-change shop should be happy to check it for free. Every two years is about right. But you also should keep your cooling system happy by running the air conditioner every few weeks in winter to keep it lubricated, checking for puddles underneath the car and replacing belts and hoses before they dry and crack.

Replacing tires when you should be replacing shocks. If your tires are wearing unevenly or peculiarly, your car may be out of alignment or your shocks or struts worn out.

Letting a brake squeal turn into a brake job. Squeal doesn’t necessarily mean you need new rotors or pads; mostly, it’s just annoying. Your first check -- you can probably see your front brakes through the wheels on your car -- is to look at the thickness of the pads. Pads thicker than a quarter-inch are probably fine. If your brakes emit a constant, high-pitched whine and the pads are thinner than a quarter-inch, replace them. If your car shimmies or you feel grinding through the pedal, then your brake rotors need to be turned or replaced.

Not complaining when your warranty claim is rejected. Check Alldata and the National Highway Transportation Safety Administration (NHTSA) to see if a technical service bulletin (TSB) has been issued about the component in question. Manufacturers often will repair known defects outside the warranty period (sometimes called a secret warranty). It helps if you’ve done your homework and haven’t been a jerk.

Not keeping records. A logbook of every repair done to your car can help you decide if something’s seriously out of whack. Didn’t I just buy new brake pads? With a log and an envelope stuffed with receipts, you’ll know who did the work and when, and whether or not there’s a warranty on the repair. And a service logbook helps at resale time, too.

Buying an extended warranty. Most manufacturers allow you to wait until just before the regular warranty expires to decide. By then you should know whether your car is troublesome enough to require the extended warranty. Most of them aren’t worth the price.

Overinsuring. Never skimp on liability, but why buy collision and comprehensive insurance on a junker you can probably afford to replace? Add your deductible to your yearly bill for collision and comprehensive coverage, then compare that total with the wholesale value of the car. If it’s more than half, reconsider.

Assuming the problem is major. If your car is overheating but you don’t see a busted hose or lots of steam, it might be the $5 thermostat, not your radiator. Or it may be that ominous “check engine” light itself that’s failed, not your alternator.

Not changing the fuel filter. Have it replaced as a part of your maintenance -- every two years or according to the manufacturer’s schedule -- rather than when it becomes clogged with grit, leaving you at the mercy of the nearest garage.

Not knowing how to change a tire. Have you even looked at your spare? Make sure it’s up to snuff and all the parts of your jack are there. Changing a flat yourself is not only cheaper, it’s faster, too.

Not keeping your tires properly inflated. Check them once a month; otherwise, you’re wasting gasoline, risking a blowout and wearing them out more quickly.

Car washes. Ten bucks for long lines and gray water? Nothing shows you care like doing it yourself.