How to check the car engine when buying a used car

Please note, this article is designed to give you an initial idea about what to look for when buying a used car and might possibly help you to avoid some used cars with potential problems, but it can not substitute for a detailed mechanical inspection performed by a professional. As a final step before purchase, take the car to a mechanic of your choice for thorough mechanical inspection. Use caution when doing any tests on a car, If you don’t feel comfortable doing any of these tests, have the car inspected by a mechanic.

Imagine, you are shopping for a used car. You enter the dealership and see that nice-looking car. You love it from a first sight. Meanwhile, the salesperson hanging around and telling you that regular story that, the car was lady driven and the engine works like a clock, and this is only "Today special" - "We need to clean inventory!", and you are so lucky because they are selling it very cheap - "We even lose money on this deal!" and that you have to give a deposit right now or else you will regret about it for the rest of your life! (Sounds familiar so far?)
You decided - "deal!" - shaking hands, you're happy, salesperson is happy. Finally, you got your new wheels.
Few weeks later you notice blue smoke when you're starting the car in the morning. Few months later you discover that there is no oil left in the engine and finally got your car towed to the garage. "The engine is gone - has to be rebuilt" they diagnose.
In fact it's quite common scenario.
This article will give you an idea an may help you to avoid such a troubles buying a used car.
However, it's always good idea to have the vehicle inspected by a specialist prior purchase. This is what I'd recommend to any used car buyer.

Things you should know before going to check a used car

When buying a used car, without a doubt, first check a car history records. Some cars may have been flooded - worthless to buy. Others were written off by insurance due to serious accident. Many cars have altered mileage, and so on.
Follow this link to learn more How to check a used car VIN history report
If looking at the used car you noted any problem with the engine (e.g: major oil leak or strong noise) or any abnormal behavior don't let the salesperson to mislead you. They may tell you, for example, that the leak is "overflow from the recent oil change" or "the noise will disappear later by itself or something like this". Generally, such defects never disappear by itself. If you have hesitation, move on - there are so many cars available.
Ask for service records if they are available. Look for oil change intervals - was the oil changed regularly? I mean driving 1,000 miles over suggested oil change interval won't cause a big damage, but, for example, 9,000-12,000 miles (15,000-20,000 km) without an oil change may cause serious engine problems in the future.

Keep in mind, that modern engines, especially those with turbo charger are extremely sensitive to the oil change interval

How to check the oil

Park the car on a level spot, turn the engine off and set the hand brake. Locate the engine oil dipstick, pull it out, wipe it off with clean cloth and insert it back. Pull it out again and have a close look. If you've never checked the oil level before, follow this link for detailed guide How to check engine oil.
If you find the oil is completely black (although for the Diesel engine black oil is normal) and (or) the oil level is very low (left picture) - suspect excessive oil consumption and (or) lack of maintenance. In either case the engine will more likely to have problems in the future. Another sign of poor maintenance would be dark stains (carbon deposits) covering the oil dipstick along its length.
Well maintained engine will more likely to have cleaner oil and the proper oil level (right picture), although this doesn't necessarily mean that the engine is in good shape; the oil just could have been changed recently.

Look for leaks

Look for possible oil leaks. If the engine looks very clean and shiny it doesn't mean it has no leaks. Probably it has been shampooed. Most of the dealers shampoo the engine before putting a used car for sale. But there is the trick - look underneath the vehicle using your flashlight. Check the lower part of the engine and transmission. Everything has to be dry. There might be slight wetness which is not that bad, but there should be no leaks. See any leaks? Oil drops on the parking space? - this may indicate a problem.

Note, the water condensations dripping from air conditioner drain tube is normal. This drain tube is usually located on the passenger side of the firewall.

If it's possible, look at the internal parts through the oil filler neck (Don't open the oil cap while the engine is running!)

Dirty engine Clean engine

Oil sludge inside the engine

With the engine turned off, try to open the engine oil cap and look inside through the oil filler hole. Use a small flashlight. If it's possible to see any internal parts there, check their condition. What you are looking for is the oil sludge - this thick black buildup on internal parts you can see on the lower photo (this is how the sludged up engine looks inside, with the valve cover removed). If you see a lot of black oil sludge buildup inside the engine it means that either the engine oil hasn't been changed for a long time, or the engine has been overheated, or poor quality oil was used.
In either case, avoid buying such a car - sooner or later it will have serious engine problems.
Well maintained engine usually looks pretty clean inside; if you check few cars of the same model it's easy to see the difference. However, again, if the engine looks clean inside it doesn't mean that it has no other possible problems - as a last step, have the vehicle inspected by a mechanic of your choice.

Check the oil pressure

Try to check the engine oil pressure on a cold engine (few hours since the engine has been turned off). Start the engine, and look at the low oil pressure warning lamp or oil pressure gauge in the instrument panel. The time between the engine start and you note oil pressure at the instrument panel should be no more than 1 - 2 seconds.
If this time is longer than 2 seconds, avoid buying a used car like this.
If the low oil pressure warning light goes on while engine is running or idle, or the engine oil pressure gauge indicates too low oil pressure, it also means that the engine is worn out or has some defect - avoid such a car.

If you find evidence of badly made repairs, avoid any such car.

If you find evidence that the engine has been repaired with inaccuracy (too much bulging of gasket maker, as in the image, loose bolts, stripped treads, altered wiring, broken fastenings, missing bolts or covers, etc.), avoid buying such a car because quality repair is possible only by very skilled mechanics. Just imagine how the engine has been repaired on the inside if it looks this way on the outside?

Check the antifreeze level in the overflow tank (never open the radiator or overflow tank cap when the engine is hot!)

Check the antifreeze (coolant) level in the overflow tank. It should be between the "min" and "max" marks, as in this picture. The antifreeze should not have even a spot of engine oil. It should be clean and transparent, it also may be of green, red, blue, orange, or yellow color (depending on the maker).
If you find presence of the engine oil in antifreeze, it may be an indication of a possible engine or radiator problem (a blown head gasket, leaking transmission fluid cooler, etc.).
Look under the car. Check the radiator and water hoses for damage, cracks or leaks. Look at the radiator, it should not have any damage.

Timing belt

Many cars, especially with four-cylinder engine, have a timing belt that needs to be replaced at a certain interval - usually between 60,000 and 100,000 miles (100,000 and 160,000 km). For example, 1993 - 1997 Toyota Corolla, 1992 - 2002 Toyota Camry, 1998 - 2001 Honda Accord, 1997 - 2001 Honda CR-V, 2001 - 2004 Volkswagen Passat - they all have a timing belt. If it wasn't replaced by the previous owner, you will have to do that. It's difficult to check it on the car because the timing belt is protected by the protective covers. The only way is to ask the previous owner if they have a receipt. Sometimes though, dealers place the timing belt replacement sticker somewhere on the top of the engine (see the picture) that indicates the date and the mileage when the belt was replaced.

Check the smoke

Start the engine. Let it idle for a 5-10 minutes. Then ask someone to press more than a half way down on the accelerator (to 4500-5000 engine rpm) for 2-3 sec. while you look at the smoke from the exhaust.
If there is cloud of grey-blue smoke, the engine consumes oil (see the picture). Avoid such a car.
Black smoke means the engine consumes too much gas - possible problem with fuel injection.
Normally, there should be no smoke at all (Diesel engine may have slight black smoke at a cold start - it's normal). A small amount of white water steam and water condensate dripping from the exhaust is normal.

Listen for noises when the engine is running

There shouldn't be strong noises, coming from the engine under any condition with no matter is the engine cold or hot. By the way, knocking or tapping at a cold start is one of the indicator of poor maintenance. Knocking, tapping or rattling noises indicate excessive wear of internal engine parts. Whistling may be caused by loose belt. If the engine makes too much noises, avoid buying such a used car (however, Diesel engines are always more noisy, it's normal).

Look at the instrument panel

There should be no warning lights such as "low oil pressure", "low oil level", "overheating", "check engine" or "service engine soon" etc. on the instrument panel when the engine is running.
I receive lot of questions about "check engine" or "service engine soon" light. You may find the explanation what "check engine" means in the article Why my "check engine" light is on
If the car has "check engine" or any other warning light coming on while driving, have the proper diagnostic done before deciding to buy the car; in some cases the problem could be very costly to repair.

Test drive

Try to test drive a car for as long as you can. Try to accelerate, decelerate, take it on the highway if it's possible. The more you drive, the more chances you discover possible problems. If it's your first car, try to test drive few different cars of the same model to have better idea. If you feel anything that may indicate possible engine problem (e.g vibrations, stumbling, misfiring, delay during acceleration, rattling noise, smoke, rough idling, etc.) avoid buying such a car. If you have any hesitation about the way the car drives, shop around, there are plenty of used cars available. Sometimes a sales person may try to push you to buy a car today and now because "tomorrow I won't give you this price" or "I have the customer who will buy this car tomorrow" - Don't rush, take your time to think, the more you shop around, the more chances to find the right car for the right price.

Mechanical inspection

As a last step prior buying a used car, have the vehicle inspected by an experienced mechanic of your choice.

Do's and Don'ts

- Don't buy a car if you see a smoke from exhaust pipe - only the water steam and water condensate dripping from the tail pipe is OK.
- Don't buy a car if engine knocks or works too noisy.
- Don't buy high-mileage cars. I'd recommend to avoid cars with more than 145,000 - 150,000 miles (230,000 - 240,000km)
- Don't buy cars that have some engine problems even if it seems to be easy to repair
- Do hire someone knowledgeable to have a vehicle inspected before you buy it.

If you are looking for more detailed technical information

If you want to find more technical information about you car such as all kind of diagrams (transmission diagram, engine diagrams, vacuum line diagram, electrical diagram, etc.) repair information, specification, fluids type, maintenance schedule, component location, service bulletins and so on, there is a website which for a small fee allows you to browse all such an information for almost any car model on-line. To learn more visit this page:
Where to find technical information about your car