testing car engine

Engine Testing Methods From The Pros


Daniel McDonald
Daniel McDonald7 min read
Engine Testing Methods From The Pros

Engine Testing Methods From The Pros

While most of you would like to own the most incredible, powerful engine under the hood, sometimes you need to comprise with an older one.

If you want to take advantage of a used one or work in the automotive industry, a few testing methods will help you become a pro. 

Start reading our guide for engine testing methods to become a pro today!  

Testing Car Engine: Visual Inspection 

Every test starts with a visual inspection – opening the hood. When you take a quick look at your engine, you should tell how well it's performing. 

You can cold start by checking for oil leaks in all familiar places. You should observe the pan's back and the crankshaft snout area.

Take off the cleaner and look at the air filter. Look if the PCV valve or hoses are damaged and do a visual inspection of the distributor, coil, plug leads, insulation, and terminals for carbon tracking. 

If your engine is leaking, even when the operating temperature is reached, you should remove all the breathers, oil filler cap, and the PCV valve hose and look if any steam is coming out. While a bit of steam is standard, your engine is worn out if there is a lot of smoke. 

Pull The Dipstick 

Another crucial thing that mechanics check while doing services on many engines is checking the oil level.

After pulling the dipstick, check whether the oil is clean; clean oil indicates that the engine was correctly maintained. If you notice any white foam or rust, there is coolant in the pan, which is not a good sign. 

If the coolant has also transferred to the breathers, it indicates that the engine is excessively moist and there is coolant in the oil.

Besides checking whether there is coolant in the oil, look for leakage in the valves or the seals. Look inside the radiator tank and the coolant hoses for rust or dirt. 

Any signs where the coolant leaks from the cooling system indicate a mechanical problem.  

Listen For Weird Sounds 

If you can run the engine, try and listen for weird noises. In general, the heavier the noise, the worst the problem. Here is a list of all the odd noises you can hear: 

  • Metal rap sound indicates a bearing problem;

  • Light ticking noise usually means that there is some cam or lifter issue;

  • Squealing noise comes from glazed or loose belts;

  • An inconsistent cranking sound means that there is a problem with the starting system or the compression; 

  • Rumbling sounds mean a bad bearing in the alternator or the water pump. 

Pretesting Procedures 

Depending on the engine testing method you perform, there is a chance you will need to do some pretesting procedures. For example, many engine tests require a disabled ignition. 

If you plan on using a remote starter switch, you should connect it before starting the engine testing procedure. Check the equipment's instruction manual to see the test equipment and whether you need to connect two or more leads.

Some of the engine analyzers are developed to move through pre-programmed tests. For example, if you plan on checking the tailpipe emissions, you need to install an analyzer probe in the tailpipe as a pretesting procedure. 

Basic Tests: Check The Battery, Alternator, and Starter 

The first tests you should develop are a series of basic engine tests. If you want the engine testing to be accurate and fast, you should group the battery, alternator, and starter tests. 

  1. Cold start by recording the battery open-circuit voltage;

  2. Impair the ignition system and do a 15-second crank of the engine;

  3. Write down the starter current, the battery voltage, and the cranking rpm; (some analyzers read the relative compression as well).

This basic test will give you an extensive view of the battery capacity and the starter condition. If the indications are out of the limits, you can do a more detailed test to spot the problem.

Another basic test you can do is to check for vacuum using the engine cranking period. The specifications for cranking vacuum vary from engine to engine.

Therefore, you will look for a steady vacuum and speed. To prove the excellent mechanical shape of the engine, the cranking rate needs to be collected at 200 rpm and the void at 5 inches. However, if the values are not even, the cylinders are not pumping as they should. 

This early testing stage is a good time to verify the volume and the fuel pump pressure. If the fuel delivery is inadequate, the engine will not start. You should test the fuel pump and compare it with the specifications.

Once you finish all these tests, your battery will likely need to be recharged. While you recharge the battery, you can continue with the alternator test. 

  1. Set off the engine and run at 2500 rpm;

  2. Note the recovery voltage of the alternator as well as the amperage output and the charging voltage;

  3. If the test records an alternator ripple that exceeds .4 volt, it means that the alternator diodes are in order;

  4. Stay at 2500 rpm and check for emissions by recording the CO, 02, CO2, and HC readings; 

  5. Next, idle the engine and record the emissions reading once again; 

  6. The specifications for these emissions may vary from state to state – still, if the engine is in good shape, it should produce less than 151 ppm of HC, less than 1.6% of CO, less than 5% of O2, and more than 10% of CO2.

  7. This test is an exceptional indicator of the general state of the engine. 

Compression Test 

One of the most critical testing methods for engines is compression testing. Here are the steps: 

  1. Remove all spark plugs, block the throttle, and disable the ignition;

  2. Crank your engine at least four or five times;

  3. The pressure should reach a value between 140 and 160 psi (it is best to check the owner's manual for the exact specifications);

  4. In case the cranking pressure is below 100 psi, you should spray a bit of oil in the cylinders and repeat the test; 

  5. If the pressure reaches above 100, the oil has sealed the rings; therefore, the problem is in the rings. If the pressure is the same as before, the valves are your problem. 

  6. When doing a compression test, you should check the consistency of the cylinders – close readings of both cylinders indicate a uniform condition. In contrast, if one cylinder has a lower value by 20%, there is a mechanical problem such as a broken ring or burned valve. 

Vacuum Test

Another way to determine whether your engine is in good condition is to do vacuum testing. Regular readings at sea level are not greater than 22 inches and no lower than 17 inches of mercury. 

If the vacuum gauge readings are low or shifting or the needle is vibrating, the test indicates that some engine components have a severe problem. 

Leakage Testing 

The leakage test is a great way to evaluate the engine cylinders. You should put pressure on the cylinder with compressed air, and it will indicate if there is a leak. The pressure should be displayed on a gauge while controlled by a regulator.

When you pressure the cylinder, you can pinpoint the leakage by listening for sounds of shallow air. 

  • If the air is coming from the carburetor, the test indicates that the intake valve is leaking; 

  • Leakage from the tailpipe indicates that the exhaust valve is not sealing;

  • If the air comes from the hiatus, the test shows that the compression is going through the rings;

  • The test demonstrates a head gasket leaks if you notice bubbles in the coolant. 

If you confirm the presence of leakage, you will need to tear down the engine completely. You should know that a new engine should show a maximum of 10% leakage, while any leakage above 30% indicates serious engine problems.   

Cylinder Testing 

An engine test is not complete without testing the balance of the cylinder. Here are the steps: 

  1. Engines need to be warm before starting with this test;

  2. Run it at 1,000 rpm and start pulling one plug wire after another;

  3. Ground the plug wires to prevent ignition system damage and sparks;

  4. If all cylinders drop at the same rpm, it means that their condition is good;

  5. If you notice the rpm drop, there is a problem that you need to investigate further. 

Conclusion 

Before doing complex engine testing, you should visually inspect the condition. If you notice any leaks and strange noises, or the oil is not clean, it is evident that there is a problem with the vehicle and further testing needs to be performed.  

A great way to determine the condition of your engine is to perform battery, alternator, and starter tests first, then move on to compression, vacuum, leakage, and cylinder balance testing.

These testing methods will reveal a problem with the individual components, such as the distributor cap, or whether the engine is working smoothly.

Make sure you compare the specifications and the trouble codes because, in most cases, different vehicles from different manufacturers have other specifications. 

If you want to do more testing, you should check if the timing chain is worn out – this can be quickly done without taking apart the engine components.

Although we didn't pay much attention to the cooling system, these indicators are sufficient to determine whether the engines have a problem.

If you are a mechanic or a part of the automotive industry, do not forget to examine all the details and do a quality check on as many vehicles as possible.  

FAQs 

How Can I Do An Engine Test? 

Automatic systems usually perform engine tests. These tests involve an electric engine brake connected to the engine and measuring devices.

Once the test is completed, the measuring devices will show a number you should compare to see if the engine is in good working condition. 

Why Do I Need To Test The Engine? 

Engine testing is necessary to determine the performance of a vehicle. It is usually done before vehicle engines go into production.  

Which ICE Engine Testing Method Is Most Efficient? 

There is a method that finds out the indicated power of one cylinder of an ICE engine that is called the Morse test. This test doesn't use high-speed indicators and can be run under specific engine speed, load, and temperature conditions. This test is a very accurate indicator of brake power.