Insider Secrets from a Top Car Mechanic

Look at the lot before choosing a mechanic

You also want to be leery of any shop where either there are no cars, which is a red flag, of course, or they have a bunch of cars in the lot. If there are a lot of cars on site, look closely to see if they have dead inspection stickers or registrations that are out of date. I knew a mechanic once who just had a bunch of old cars lying around to make it look like he was busy when he wasn't.

Self-check the check-engine light

Even tiny things can turn the check-engine light on, so it’s sometimes hard to know whether it’s really something serious. You can buy a cheap onboard diagnostics (OBD) scan tool online for about $30 or less, and it will give you a code, which you can Google, to find out why your check-engine light is on. That works on any car made from 1996 to today. Sometimes it'll be something as simple as your gas cap is leaking or you've got a problem with your radio system. A good rule of thumb: if you drive down the road and your check-engine light isn't just on, but it's flashing, that's a pretty serious problem, so you’ll want to figure out what it is relatively soon.

Never let your gas get below a quarter of a tank

Don't run your car until it's on E and almost out of gas, because all modern cars have a fuel pump in the gas tank. And as nutty as it sounds, the fuel is what lubricates a fuel pump. It's electronic, and the gasoline that flows through it lubricates the bearing. So if you actually do run out of gas in a modern car and it stops running, your pump sucks air and can burn itself up. And replacing some of these pump assemblies might cost you $1,000 just because you decided to run the fuel too low. So I always tell people to pretend that a quarter of a tank is empty. When it gets to a quarter of a tank, go fill it up.

Take simple steps to improve gas mileage

You want to keep the air pressure in your tires set to the recommended amounts, because if it's too high or too low, there's more friction, and you could experience worse gas mileage. You also don't want to carry a bunch of excess weight. Let's say you're a bodybuilder. Don't leave weights in the trunk. Never drive around with excess weight that you don't need in the car.

Change your own air filters

Replacing filters is an easy DIY fix on most cars. For example, the cabin air filter that filters the air in your AC system is usually found behind the glove box. If it gets dirty, your car will stink, and it'll strain your AC system because it won’t be getting enough airflow. You can watch a video tutorial online to learn how to take the cabin filter out with a screwdriver so you can easily do it yourself in five or 10 minutes. But if you go to a garage, they might charge $100 or more. To save even more, plan ahead and order the replacement filter on Amazon for $6 rather than paying $25 at an auto parts store.

Go beyond the CARFAX when buying a used car

Before buying a used car, you’ve got to pay a mechanic to check it out, because it could be wrecked, flooded, stolen — who knows? Any good mechanic can spot that stuff within an hour of checking out a car. Of course, first you want to look at the car yourself. Go under the car and see if it's rusted. Once a car is rusted, that's it. It's not worth anything. If you see rust, run away from it. But if it looks all right, then you want to drive it around. If you think it's OK, you’ll want to have a mechanic take a look. That’s how you’re going to catch things like signs of a wreck that maybe wasn’t reported to CARFAX, a vehicle history reporting service. (AutoCheck.com and VinAudit.com can provide similar information.) Dealers don’t necessarily like for you to have your own mechanic check out a car, but if they want to sell it, they pretty much have to allow it.

Don’t neglect your tires

It’s important to stay on top of tire wear and tear, because when the treads get thin, you could hydroplane in the rain. You can use a penny to check the treads. Place the penny in your tire grooves so that Lincoln's head is aiming down into the tread. If you can see the top of Lincoln's head, there’s too much wear, and it's time to get new tires. Also, check for cracks or other signs of dry rot to avoid a blowout on the highway. Most people drive 15,000 miles or so a year, so they’ll need new tires roughly every three years. But if you don’t drive your car a lot, you should replace the tires every six or seven years — even if the tread is still intact. Keep a little note in your glove box noting when you bought the tires, so you’ll know when it’s time to replace them.