Can Old Cars Pass Emissions?

The Clean Air Act is devised to reduce pollutant gases emitted from cars and help preserve the environment. As a car owner, you may be required to pass the emission tests specified by your state. But what if you have an old car? Can old cars pass emissions?  

Old cars can pass emissions if they’re in good shape. To pass emission tests, you should take good care of your car, change its oil, refill fluids, clean out the engine and catalytic converter, and also tune it to run on a lean air-fuel mixture. A pre-test can also ensure it’s in good condition. 

Keep reading the rest of this article to learn more about an emission test and how to prepare your old car to pass this test. We’ll also tell you why you may fail a test and how to fix it. 

Table of Contents

What Is an Emissions Test?

Whenever you want to renew your car insurance or your vehicle registration, your car should go through some tests to ensure it’s in good condition. While the first Clean Air Act was in place before 1990, Congress amended it in that year to give more authority to the EPA (Environmental Protection Agency).

The EPA outlined a set of standards for motor vehicles’ emissions to minimize the hazardous air pollutants released by them.

As a result, your car probably needs to pass a set of periodic testing to ensure it’s within the EPA standards and has limited negative effects on the environment.

Today, emission tests are required in more than 30 states by law; however, they vary in degree by state or even county. So, you should learn about your current state’s requirements to see if it’s mandatory and what kind of testing to expect. At the end of this article, you can find a helpful guideline.

Old Cars and Emission Tests

If you have an old vehicle, you may be worried about passing an emission test, and that’s quite reasonable. When a vehicle ages and its mileage goes up, it may encounter several technical issues – especially if not well-maintained.  

Old cars can pass the emissions, too. If your car is well-maintained and you’ve serviced it regularly, probably there’s nothing to worry about. You can also perform a mock test before the actual test and repair parts if needed. Classic and collector cars are usually exempted as they’re so few and less driven.

Here’s how to make sure your car will pass emissions:

Cars Before 1996

In the emissions tests performed on old cars (before 1996), the emitted gases from the tailpipe are measured by a dynamometer test. While you’ll never be able to eliminate your car’s pollutants, you still can make it emit harmful gases within the EPA standards.

For an old car to pass the emissions tests, you must make sure everything is working properly. The first step can be changing your car oil and filter just before the inspection to have the cleanest oil.

Dirty oil can make the PCV system (positive crankcase ventilation) suck a lot of dirty vapors and produce more pollutants by burning them up. A dirty air filter also can block the air and cause the car to run lean, producing lots of pollutants.

When your car runs lean, the engine gets hotter, which leads to hotter exhaust gases, too. This rise in exhaust temperature, in turn, leads to emitting more NOx (Nitrogen oxide) – a pollutant that’s measured on the test.

Spark plugs are also vital. You should make sure they’re in good shape. If they’re old and worn out, they won’t work correctly and lead to more pollutant production.

Since tests are performed on a dynamometer, the car isn’t actually moving. So, it’s important to ensure your car’s cooling fans are spinning properly. These fans suck the air in and prevent the engine from getting hot – which leads to the emission of more pollutants. 

A loose or leaky gas cap may be easily neglected, but it can also put you in real trouble. This issue is usually among the first things inspected during the test, but you can fix it easily and on the go. Check on it and make sure it’s tight enough. If it still leaks, simply replace it with a new one before it makes you fail the test.

Cars After 1996

If you have a newer car (above 1996), it’ll be tested by plugging it into a computer and checking for possible problems.

First of all, you should fix the issues that have caused your “check engine” light to turn on because it indicates a specific trouble code that their computer decodes. Check all the things we mentioned above about the older cars and see if the light turns off or not. If it’s still on, pouring a fuel cleaner into your gas tank may help.

It usually works like magic and helps you pass the test. But if your car isn’t running well and has a serious problem, it can’t help. You should fix all significant issues before you head to the test. 

Here is very a good video that helps you prepare your car for emission test, DIY:

Tips To Pass an Emission Test

Can Old Cars Pass Emissions

Although old cars are more at risk of failing emission tests, you still can pass them successfully without getting fined. Here are some additional tips that can help you pass the test. 

Turn off the “Check Engine” light

This tip may not apply to all old cars because the check engine lights were not so common in the 1980s and only cars with computerized engine controls enjoyed them. But in 1996, they became mandatory for all cars sold in the US. A blinking check engine light, even on an old car, indicates engine issues. 

Speed up Your Car on the Highway

As time passes, your car’s catalytic converter chokes up and needs to get cleaned out. A simple way to do that is to drive at a really high speed on a highway for about 30-45 minutes; the catalytic converter heats up, and all the deposits clean away. Just remember to do this a few weeks before the testing appointment. 

Change the Engine Oil

Changing the engine oil can enhance its performance considerably. If it’s been quite a while you haven’t done it, consider changing it before heading to an emission test. Fresh oil lubricates your engine parts to ensure they run smoothly. Plus, it reduces the harmful gases it may release. 

Tune Up Your Vehicle

Tuning a car means modifying it in a way that optimizes its performance and makes it more efficient. It can also dramatically change the volume of harmful emissions that come out of your car. You should tune it to run on a lean air-fuel mixture. Keep it that way, at least till you pass the test. 

Proper Inflation of Tires

One of the things that affect fuel efficiency is low tire pressure. According to NHTSA (the National Highway Traffic Safety Administration), every 1 percent reduction in tire pressure correlates to a 0.3 percent decrease in fuel economy. It also indirectly leads to producing more harmful emissions.

Top off All the Fluids

Before going for a test appointment, make sure all your car fuels are topped off. The car will be taken to a very high speed during emission testing to check its performance and efficiency. And if your car fluids are low, it would put you in trouble passing the test – and you’ll have to pay for such a mistake. 

For example, if your car’s coolant is low or dirty, your engine gets hotter, leading to more pollutant production. 

Clean the Engine System

This tip is very simple yet incredibly helpful. Use a fuel system cleaner that is high quality and contains a strong detergent called Polyether Amine. Such a fuel system cleaner will clean up the carbon buildups on the key engine part. As a result, less carbon emissions will be released by your car during the testing. 

Do a Pre-test

If you’re not sure about your car’s condition and still doubt it might fail the emissions test, a mock inspection would give you confidence. In some states, mock tests are available to ensure that everything is okay before you go for a real test. After the mock test, you’ll have the chance to make adjustments and repairs.

Watch this instructive video to learn more about how to get ready for an emission test:


Many old cars work well, but they may fail in the emission tests. They usually produce and emit more harmful gases through the exhaust, and these are measured during the tests. However, if you maintain your car well and keep it in good shape, you can still pass the emissions tests. Simple measures like changing the oil or air filter can dramatically enhance your chance to pass the test with flying colors.

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