How to check the car engine when buying a used car

Updated: January 12, 2014
Inspecting a used car

When shopping for a used car, the condition of the engine, transmission and the car body are the most important. The fact that the car looks 'clean' and drives well doesn't mean much if its engine has a hidden problem or was poorly maintained by previous owners. Engine repairs are very expensive. Of course, it's difficult to evaluate the mechanical condition of the engine during a quick test drive, that is why we strongly recommend to have a used car properly inspected by a qualified mechanic before signing the contract. To help you be more informed, here are a few tips how to spot signs of engine problems or lack of maintenance when checking a used car.

Check used car service records

The service records are not always available, but it helps if the dealer can produce some proof that the vehicle was maintained regularly. If you can get access to the service records, look for oil changes and mileage records. It helps if you can verify that oil changes were done regularly. Depending on a manufacturer, the recommended oil change interval varies from 3,750 to 10,000 miles. If the vehicle was driven between oil changes for much longer intervals than recommended, the engine might be worn inside.
If a car has a timing belt (not all cars have it), see if there is any records that it was replaced. Typically, a timing belt needs to be replaced every 60,000 to 105,000 miles, depending on the vehicle. If it hasn't been replaced yet, it might cost you from $200 to $750 to have it done. Read more about a timing belt.

Have a look under the hood

When you are checking a used car at a dealer's lot, have a quick look under the hood before the test drive. It helps if you have a small flashlight. Make sure, the engine is off, the transmission is in "Park" and the parking brake is on. What you are looking for are the leaks, smell of burnt oil or antifreeze, signs poor quality repairs or lack of regular maintenance and 'racing' modifications.
If everything looks clean and shiny, it doesn't yet mean much, as car dealers often clean their used cars under the hood before showing them to potential buyers. Let's see some examples:

Signs of poor maintenance

Corroded car battery

If the battery looks like this, it's very unlikely that this vehicle has been maintained regularly.

Burnt oil smell under the hood

Shiny engine compartment

This Audi looks clean and shiny under the hood but we noticed a strong burn oil smell, which is a sign of possible problems.

Leaks

Coolant leak

This car runs fine, but a close inspection revealed the coolant leak from the radiator. As a minimum, this car requires a new radiator, but sometimes, a cracked radiator may be a sign of more serious problems. It's best to avoid used cars with this type of issues.

Engine from underneath

Watch out for oil leaks too. They may not be visible from above, but here is the trick - look underneath the car using your flashlight. Check the lower part of the engine and transmission. Everything has to be dry, like in this car. There might be a slight wetness which is not too bad, but there should be no leaks.

Low oil level

Low oil level on the dipstick

We checked the oil level in this car, and it's very low. Oil looks dirty too. This means that either this engine consumes oil or it was very long since the last oil change was done. In addition, the engine wears faster when low on oil. Normally the oil level should be close to "Full" mark.

Correct oil level on the dipstick

Engine oil in this car looks clean and the level is OK. It looks like the oil change has been done recently.

With the engine off, check under the oil cap

Oil cap

This test can tell a lot about the engine. If you aren't comfortable doing this test, leave it to your mechanic. With the engine off, remove the oil filler cap and look under it.

Checking under oil cap

For example, in the left photo, you can see there is a lot of black carbon deposits under the cap. The visible internal engine parts and the oil cap itself look very dirty too. Usually this is a sign of poor maintenance. In the right photo everything looks clean.

Watch out for performance mods

Engine performance mods

Be careful if a used car has some performance mods. If done right, the modifications can greatly improve the vehicle performance. However, poorly done engine mods can lead to many problems, especially if parts that were originally on the vehicle are no longer available. If the car has been modified, it's also likely that it has been raced or otherwise abused.

Cold start can reveal many hidden problems

The best way to catch hidden engine problems is to start it cold. To do this, it might be a good idea to come to the dealer a little earlier than your appointment time. First thing that this will reveal is how good is the battery, because if the battery is old, it might need to be boosted to start the car. Another thing to look at a cold start is the engine noises. If the engine rattles or makes other loud noises, it might be excessively worn or has some mechanical problems. Similarly, a blue smoke at a start-up means the engine is worn and it's best to look for another vehicle.

'Check Engine' light stays on

Check Engine light on the dash

After the car is started, all warning lights on the dash should come off. For example, in this car, the engine symbol that is known as "Check Engine" light remained on after it was started. This means that the engine computer detected some fault. It could be a minor issue, but it also could be a very expensive to repair problem. There is no way of knowing how serious is the problem until the car is properly diagnosed. Read more what "Check Engine" light means.

Smoke from exhaust

Blue smoke from the car exhaust

Here is another example: we started this car and noticed a blue-gray smoke from the exhaust. It smelled like burning oil too. A blue smoke means that the engine burns oil. Cars like this should be avoided.

Test drive

During the test drive, watch out for engine noises, vibrations, lack of power, or any other driveability issues. When started, the engine should run smooth, without shaking or hesitation. If you feel that the engine is bucking or stumbling when accelerated, there is a problem. The idle speed should be stable too. Test drive for as long as possible; sometimes problems may not be obvious during a short drive around the block. It's best to try the car in all modes: acceleration, deceleration, stop-and-go traffic, highway cruising. Watch out for the engine temperature on the dash. Once the engine is warmed up, the temperature gauge should stay somewhere around the middle of the scale.
Even if everything seems OK, we strongly recommend to have the used car properly inspected by an independent mechanic before buying.

Read more:

Illustrated used car checklist
Signs of transmission problems when test-driving a used car
How to buy a used car, step by step