How To Evaluate and Test Drive a Used Car

If you're going to buy a used car, then you want to get the best car you can for the money. Unless you're buying the car from someone you know, in most cases the inspection and test drive will be your only chance to evaluate the car that you're considering. Here are some ideas to help weed out the lemons.

Unless you're a gearhead, you may want to consider having a mechanic inspect the car you're considering buying. There are many mechanics who make a living from inspecting used cars for potential buyers. Hiring one of these experts is something you should consider if you're not mechanically inclined (or even if you are, but cars aren't your specialty). Most garage mechanics will also be happy to do this for you if they're not too busy with actual repairs, but usually they'll want you to bring the car to them. If the seller's okay with that, then it's a perfectly acceptable way to go.

Either way, be realistic in your expectations. Cars are very complex machines, and not even a skilled mechanic can guarantee that a car that seems fine today won't suffer an expensive-to-repair breakdown tomorrow. There are just too many parts, and many of them are not accessible for inspection. But a good mechanic can at least get an idea if the car seems well-maintained or if the seller is pulling any shenanigans to try try to cover up an obvious problem.

If money is tight, you may want to have a gearhead friend who's skilled in car mechanics accompany you to check out the car. If you live near a college or trade school that teaches auto mechanics, you may also be able to hire one of the students to help you out for a lot less than a professional would charge. A lot of them are pretty good.

Performing Your Own Used Car Inspection

If you're going to do your own inspection, here are some things you should check for. This is not an exhaustive list, by the way. I've selected the things that tend to be most revealing of a car's condition, but which an average non-mechanic should be able to do.

When showing up to inspect a used car, try to schedule the inspection for a sunny day. Be sure to bring a flashlight and an inspection mirror with you, as well as a pair of safety glasses to keep rust and dirt out of your eyes while you're looking under the car. Wear old clothes or coveralls because you're going to get a little dirty. A simple voltmeter or multimeter can also come in handy for checking the battery and electrical system.

If you have or can borrow an OBD2 code reader or scanner and know how to use it, that's a big plus. OBD2 codes can reveal a lot about the condition of a car's engine, emissions system, and transmission.

There are two kinds of devices that can read OBD2 codes: readers and scanners. Readers only show you what the codes are. Scanners can monitor many aspects of the car's systems in real time and are more expensive than readers. If you are or would like to be a shade tree mechanic, then a scanner is a better bet because it will help you to diagnose and fix problems. If you just want to read codes, then a reader is less expensive. There also are inexpensive phone and tablet apps that can be used as scanners if you purchase a compatible OBD2 Bluetooth adaptor.

Here's my suggested routine for inspecting a used car. Important Safety Note: Car engines have a lot of moving parts, and some of them only move intermittently. Keep your hands well away from the engine, belts, pulleys, fans, and anything else that looks like it may move.

When you first approach the car, look at it from 10 or so feet away. Walk around the car in a big circle and check to see if it leans one way or the other or appears "bent" or "tired."
Look for rust on the body, broken or cracked windows, dents, dings, and so forth. Also observe whether some of the body panels have a slightly different color or sheen from the others. That usually means that the car was repaired after an accident.
Look under the car. Check for oil or fluid leaks and drips, as well as rust on the frame, fuel tank, oil pan, suspension parts, and so forth. A bit of rust is normal, but if the metal parts look like they're rotting away, then they probably are.
Check for broken suspension springs, leaky shock absorbers, and rusty or rotted-out exhaust system components. Tape around an exhaust system component is also a bad sign. It means there's a hole under the tape and the exhaust system is starting to rust or rot away.
Inspect the tires for remaining tread, bubbles, gashes, wear marks, and so forth. Also check the wheels ("rims") for excessive rust, dents, or out-of-roundness. Very rusty wheels can be a sign that the car was submerged or was operated in a harsh environment. Dents, dings, or out-of-roundness mean that the driver had a habit of hitting curbs, potholes, or other immovable objects.
Grab each tire with your hands and try to shake it both vertically and horizontally. If there's play, then the car probably needs wheel bearings or suspension / steering parts. These repairs can be expensive, but these are parts that do wear out over time; so if the car's otherwise in good shape, you may want to factor the repair costs into your offer rather than walking away from the deal.
Open and look under the hood. Look for oil stains, especially around the parts of the engine that join to each other, such as where the block meets the head, the engine meets the transmission or transaxle, and so forth.
Look very carefully at the place where the head meets the block. That's where the head gasket is. It's a cheap part that can cost thousands of dollars in labor to replace on some cars. Any oil or water leaks, gunk, or anti-freeze residue around the head gasket is a very bad sign. Walk away from that car. It's not just the head gasket that's the problem. It's the fact that you don't know what caused the head gasket to fail. It could have been a serious overheating event that caused other problems, as well.
Pull the oil dipstick. Make sure it's not overly low or overly full. Either one is a sign of shoddy maintenance. Also make sure there are no water bubbles in the oil. Water in the oil is a sign of a bad head gasket or damage to part of the cooling jacket (for example, a cracked head). Also be suspicious if the oil seems thicker than it should be. Putting heavy oil or thick additives into the oil to temporarily seal a leak when selling a car is an old trick.
If the engine is cold, open and peer into the coolant reservoir. If the coolant is brownish, then someone put radiator seal in it. That usually means there's a leak in the cooling system that they tried to plug up. If the coolant has any oil at all in it (it could be just a very thin sheen on the top of water), that's a symptom of a bad head gasket or other engine damage.
If the coolant is brand new and perfect-looking, on the other hand, then it could be that the seller is trying to hide a problem. But it can also mean that they're just good about maintaining the car, so don't make a decision solely on that basis.
There's a gasket more toward the top of the engine, where the valve cover attaches to the head, that amazingly enough is called the valve cover gasket. Minor leaking at the valve cover gasket is common on older cars, and usually it's an easy repair. Serious oil leakage, however, may mean a serious problem that caused the pressure inside the engine to blow out the seal. More often, however, a leaky valve cover gasket is just a sign of an owner who was less-than-meticulous about maintenance.
Check to make sure that the spare tire, jack, and tools are present. These usually will be in the trunk somewhere.
If you brought a voltmeter, set it to the closest range to 15V DC. Then test the resting voltage at the battery with the engine off and nothing electrical turned on. Red goes to positive, and black goes to negative. If the voltage is much less than 12V, the battery will likely need replacing soon. Then turn on the headlights and test again. This is the battery's voltage under load. If the voltage is much less than 11.5 volts, the battery will likely need replacing soon.
Check the belts for wear. It's hard to tell sometimes, but if they're very loose, if threads are sticking out of them, or if they just look old, that could be a sign of lackadaisical maintenance.
Get in the car and turn the ignition to the ON position, but don't start the engine. Look at the instrument panel and make sure that all the indicator lights are lit, especially the check engine light. They should all be lit when you first turn the ignition on. That's how you check that the lamps aren't burned out or missing. We'll talk more about this a bit later.
Start the engine. Look at the instrument panel again and make sure all the idiot lights have gone out. Let it run for a minute or so. Then go back outside, lean over the engine (be careful of moving parts!), and start sniffing. If you smell exhaust, then the car has an exhaust leak. If you smell anti-freeze (it has a sweet smell), then the car has a coolant leak. If you smell gasoline, then the car has a leak in the fuel system. Obviously, none of those are good signs.
Listen for tapping, knocking, and hissing noises, as well as for the engine's general smoothness. Note that on some cars, an emissions pump may run for about a minute when the car first starts, which can cause a hissing or whooshing sound. This is normal for those cars and is nothing to worry about.
Shine your flashlight around the engine while it's running and look again for oil or fluid leaks. Keep your hands away from moving parts!
If you brought a voltmeter with you, test the voltage at the battery again while the engine's running. Be careful of moving parts! If the voltage is much less than 13.5 volts, the car may have a problem with the alternator, voltage regulator, ground strap, or wiring.
Shut off the engine and remove the key. Wait a minute or so, during which you can ask the seller about the car's maintenance records. What you want is evidence that the car has been well-maintained in general, and especially that major maintenance that should have been done at certain intervals has been done, such as the timing belt, fuel pump and filter, and so forth. Ideally, the owner should have receipts for maintenance or parts.
If you brought an OBD2 reader or scanner, check the OBD2 system as described below.

How to Use an OBD2 Reader to Check a Used Car You're Thinking about Buying

In previous versions of this site, I mentioned taking OBD2 readings as part of the inspection, but some readers told me my explanation was inadequate and confusing. So let me go into a bit more detail.

OBD2 (or OBD-II) for "On Board Diagnostics Version 2" and is a diagnostic system built into all cars built since 1996, primarily for emissions-control reasons. It replaced an older, rudimentary system called OBD1, or simply OBD. The OBD2 system constantly monitors many aspects of the car's operation, and when some value is outside the boundaries that the system expects, it issues a "code" and lights the CEL (Check Engine Light).

An OBD2 reader reads OBD2 codes, and nothing more. An OBD2 scanner also reads codes, plus is also able to read a great deal of information about the car's systems in real time, as well as control some of the systems. Unless you know how to interpret this information, you can just use a reader. They're less expensive than scanners.

The OBD2 port is usually located under the dash on the driver's side

To use an OBD2 reader, simply insert it in the OBD2 port, which almost always is located under the dashboard on the the driver's side. Turn the ignition key to the "ON" position without starting the car. Then wait for the reader to query the OBD2 system and report the response, which can take anywhere from a few seconds to a minute or more. The response will either be no codes, pending codes, or "Not Ready."

An OBD2 code doesn't necessarily mean that the part the code refers to has failed (although that's sometimes the case). It merely means that a value was outside the normal range. In other words, if the code refers to one of the many sensors in the car, it doesn't necessarily mean that the sensor has failed. The sensor may have failed, but it could also be accurately reporting a problem in whatever system it monitors.

The reason I mention this is because if a car has a code and the seller tries to tell you something like, "Oh, don't worry about that, it's just a ten-dollar part," that means nothing. The sensor might be perfectly fine and accurately reporting some other problem in the car which may not be such an easy and cheap fix. A good rule of thumb is to never buy a car with a code or a lit CEL without having a mechanic look at it first. If the seller won't let you have a mechanic inspect the car, then walk away.

Another time you should walk away is if you try to check for codes and the reader or scanner gives you a "Not Ready" message. What that means is that the seller either cleared the codes with a reader or scanner, or disconnected the battery, which has the effect of clearing the codes on most cars. It also has the effect of temporarily turning off the CEL for codes associated with tests that take several drive cycles to complete. Until the car has been driven enough to complete those tests, the CEL will remain unlit.

In other words, if the system reports "not ready," then the seller is probably trying to rip you off. They most likely cleared the codes so the CEL would not be lit when you test-drove the car. If you buy the car, the CEL will come back on once you've driven it a few times; and the seller's problem will have become your problem. The only other explanations for a "not ready" reading are that the seller just had some work done on the car that required disconnecting the battery, or that the car was sitting unused for a very long time and the battery went completely dead. In any case, I suggest you either walk away or consult with a mechanic before buying any car with a "not ready" OBD2 indication.

Another type of code that's cause for concern is called a "pending" code, which can be thought of as a code that the OBD2 system isn't yet sure that it wants to issue. Some codes require that a certain value be out-of-range more than a certain number of times before a code is issued or the CEL is lit. Until that happens, the code is stored as pending, and the light stays out while the system makes up its mind. Some pending codes can be signs that a part is getting ready to fail; so again, it's a good idea to talk to a mechanic before buying a car with a pending code.

If there are active codes, there should also be a lit CEL. If there are codes but no CEL, then it's possible that the seller pulled the bulb behind the indicator and is trying to pull a fast one on you. It's also possible (though very unlikely) that it simply burned out. Either way, it's a suspicious thing. Most codes also light the CEL. If that's not the case, then I suggest you walk away or consult a mechanic.

If there are codes and the CEL does light up, then write down the codes so you can talk to a mechanic about them. The same goes for pending codes. Some are easy and cheap to fix. Others, not so much.

Finally, just because the system is ready and there are no codes, that doesn't mean the car is in good shape. All it means is that the systems the OBD2 system is programmed to monitor are not reporting any out-of-range values. The car may still have problems that don't cause codes. So in other words, the absence of codes is a good sign, but not a guarantee that the car is problem-free.

How to Test-Drive a Used Car

Before test-driving a car, make sure that it has a current registration, inspection (if required), and insurance. Ask the seller, and if you have doubts, ask to see proof. You can be ticketed for driving a vehicle that doesn't meet these requirements.

My suggested routine for test driving a used car is as follows.

If you haven't done so already, sit behind the wheel, turn on the ignition without starting the car, and see if all the indicator lights are lit as described earlier.
Start the car, and while it's warming up, check the indicator lights again, and test all the driver-controllable things like the lights, radio, heat, air-conditioning, power windows, mirror, seats, and so forth. Observe how smoothly the car idles and if the engine speed settles down to where it should be (usually between 600 and 1,000 RPM, although it does vary between car models) after a minute or two (maybe longer if it's cold out).
Gradually depress the accelerator pedal to about 4,000 RPM (or about three-quarters down if there is no tachometer), hold it there for a few seconds, and then gradually let up on it. Check for uneven acceleration, hesitation, shaking, backfiring, spitting, sputtering, farting, and so forth on both acceleration and deceleration.
If the car has a manual transmission, depress the clutch, put the car into first gear, and slowly let out on the clutch until the transmission starts to catch. Then shift back into neutral and release the clutch normally. The purpose of this test is to roughly determine how worn the clutch is. Basically, the lower the clutch pedal is when the transmission starts to catch, the more life is left in the clutch.
Take the car on the road and operate it at low speed for a while, making several left and right turns. Listen for any "clunks" or other noises and get a feel for the car's front end. There shouldn't be excessive play, but it also shouldn't be too stiff, either. Either could be a sign of front end problems.
At some point when it's safe to do so, accelerate the car to about 30 MPH, relax your grip on the steering wheel, and apply the brakes to come to a full stop. The car ideally should come to a straight stop, with the steering wheel staying pretty much straight. If the car veers, pulls, dives, or swerves, or if the steering wheel moves, then there could be an alignment problem, a tire problem, or a brake system problem. (Obviously, if the car does start to swerve, grab the steering wheel and correct it!)
On a road where it's legal and safe to do so, accelerate to highway speed. Apply slight steering pressure to the left and to the right like you're changing lanes, and feel for any shaking or shimmying. This can be a sign of something cheap to fix (like wheel balancing), or of something expensive (like a wheel bearing or other front-end work). Shimmies due to wheel balance problems tend to be more speed-dependent, while shimmies due to front-end problems tend to be more steering-dependent.
When it's safe to do so, slow the car a bit by applying the brakes while on a straight section of road, and see if the car veers, pulls, or swerves while braking. You don't need to come to a stop. Just slow down some. Then resume highway speed.
When it's safe to do so, carefully allow the car to decelerate on its own as much as is safely possible without touching the brake, clutch, or transmission. This is easier to do if you're on a slight uphill stretch of road or a long exit ramp. The purpose of this test is to allow the OBD2 system to perform certain tests that are only done during engine braking or gradual deceleration.
Take note of how the transmission behaves. If at all possible, take part of the test drive on a road with steep hills, and feel for any slipping while accelerating uphill. If the engine speed increases but the car's speed doesn't while in the same gear, then the tranny or clutch is slipping.
Return back to the seller's location, getting a general feel for the car's ride and handling. Then park the car, shut down the ignition, and remove the key. Wait a few moments, and start the engine again. Check again to see if the "Check Engine" light is on. Then shut down the engine.
Pull the oil dipstick again, and check for water bubbles or foam.
Check the OBD2 system again as described earlier.

Yes, this is a pretty complex sequence. Its purpose is to test for problems that the car is likely to have by putting it through a compressed simulation of all of the common driving situations. Some of the tests are subjective: You're basically judging the car by the way it "feels." Others are designed to encourage the OBD2 system into issuing a code and lighting the CEL if there's a problem.

Even if you're not especially mechanically inclined, following this sequence will give you a better idea about the car's condition than just randomly driving it around the block. But in the end, it's still a gamble. If possible, you really should have a mechanic or a friend who's skilled in these sorts of things go with you, if you're in doubt.

The most important thing to remember is that there will never be a shortage of used cars. If something doesn't feel right to you, then consider walking away or lowering your offer accordingly. Used cars are placed on the market every day. It's much better to wait for the right one than to get stuck with a lemon.

I hope these suggestions have been helpful to you. Good luck in your car search!