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What Happens if You Don't Change Your Vehicle's Oil?

Oil is the most important fluid your vehicle needs to run. Even though it needs oil to lubricate engine parts, oil does much more than that, and when it is not changed, it wears out.

When oil wears out, it breaks down and loses its effectiveness. It becomes sludgy and cannot flow and lubricate as effectively, causing many potential engine related issues.

What Does Oil Do?

Most people understand that oil is a lubricant and that it keeps the moving parts of your engine working smoothly. There are several direct results of oil keeping engine parts moving smoothly, but there are other lesser-known jobs that oil performs too. 

oil lubrication system

Cleans Engine Components

One of the biggest and most overlooked jobs that modern motor oil performs is cleaning your engine and its components. Many oils, especially synthetic ones, have many different additives to help your engine stay healthy.

One of those additives are detergents that clean your engine components of sludgy buildup. This, in turn, prevents fouling and improper sealing of valves and many other moving engine parts.

Prevents Buildup and Corrosion

Another common oil additive is dispersants. These chemicals work with detergents to prevent further buildup once the components have been cleaned. Their goal is to produce a thin coat of protection on moving components so that sludge and carbon cannot attach or burn themselves on to surfaces.

Cools Engine Parts

Engine cooling is one of the direct results of engine lubrication. The slipperier a surface is, the more easily a fast-moving component can slide over it. When that surface is free of dirt, thick sludge, and other contaminants, a part that moves across it produces less heat (friction).

This is easily demonstrated by rubbing your hand against a smooth table then against a carpet. Moving your hand over the table produces heat eventually, but moving your hand over the carpet produces more heat much quicker. 

Reduces Wear and Tear

Another direct result of lubrication is the reduction of wear and tear on engine components. Using the example above, your hand may suffer rug burn on the carpet but is less likely to suffer the same on the smooth table.

When oil breaks down, it loses its ability to lubricate properly and becomes less viscous – a fluid’s ability to flow. A decrease in effectiveness and viscosity leads to more friction and potential damage from parts rubbing.

Seals and Prevents Leaks

You cannot stop an oil leak by pouring oil onto the leak, but some oils have additives that work to prevent or even stop small leaks.

Additionally, changing the oil alone is enough to at least prevent many common oil leaks. Oil works to keep engine gaskets and seals moist, and thereby preventing cracking. Seals and gaskets also tend to shrink, shrivel up, or disintegrate when they are not moistened.

Operates Certain Engine Components

Some modern vehicles with complex engines and auxiliary components use oil and oil pressure to operate them. Many variable valve timing systems on vehicles use oil pressure to regulate these systems.

When the oil pressure becomes too low as a result of oil becoming sludgy or too old, these systems will not function properly. Unfortunately, many are very expensive to fix when they fail.

What Can Happen if You Do Not Change Your Vehicle’s Oil?

draining old engine oil

Because oil is so important to the main component of your vehicle – the engine – not changing it regularly can result in some of the worst and most costly consequences any vehicle component can face.

Decrease in Engine Efficiency

The least consequential outcome of not changing your vehicle’s oil will be a decrease in engine efficiency. This is a result of components needing to work harder to both push the oil to where it needs to be and to pass over less lubricated surfaces as everything moves.

A small difference can have a huge impact since the engine moves at tremendous speeds, and fuel efficiency can take a nosedive.


Overheating is a result of increased friction as oil breaks down and cannot lubricate as well. Overheating once or twice may not have an immediate effect on the engine if it is caught and prevented.

Persistent and long-term overheating can cause internal parts to warp and bend under the immense pressures of the engine. This will result in an engine rebuild if not addressed.

Poor Engine Performance

Another relatively minor consequence of old oil is a decrease in engine performance. This is partly due to the engine itself having to work harder to do the same things you want it to do with fresh oil.

The other part is that the oil also becomes less effective, so sludge can buildup, the engine can become clogged with contaminants, and oil pressure may not allow certain components to function at their peak potential.

Engine Failure

The ultimate result of not changing the oil in your vehicle is a total failure of the engine. Each of the aforementioned consequences will eventually lead to total engine loss if not addressed when the signs and symptoms of old oil manifest themselves. This is one of the costliest repairs any vehicle can have.

What are Signs and Symptoms that Your Oil Vehicle’s Oil Needs to be Changed?

Fortunately, there are several signs and symptoms of not changing your vehicle’s oil that can alert you to a potential problem before major engine damage occurs.

Read More: How Long Does an Oil Change Take?

Less Efficiency

Decreased fuel and engine efficiencies are both consequences and signs that your oil needs to be changed. More frequent trips to the gas pumps can alert you to a problem.

Many people keep track of exactly how many miles per gallon their vehicles achieve each time they go to refuel. This can be helpful if you suspect that you are spending more on fuel costs than you should be.

Noticeable Decrease in Performance

Nobody knows how your vehicle runs better than you. Driving it everyday familiarizes you with the normal sounds, feels, and smells of your vehicle, and when it starts acting different, it is a sign that something might be wrong.

Quick acceleration may be the only thing that alerts you to an issue but not running correctly, in general, can also be the sign of the oil needing to be changed.

Low Oil Measurement

dipstick check

One of the easiest things to do in any vehicle is to check the oil. The dipstick has markings for low oil levels to show you exactly how much needs to be there. When you pull the dipstick and it is low, you should check when your last oil change was completed. It may be that you need another one sooner rather than later.

Smelly or Visible Exhaust

Normally, your vehicle should not smell like exhaust fumes, nor should you be able to see exhaust coming out of the tailpipe – unless perhaps the weather is very cold.

When this happens it usually means that there is some kind of overheating occurring or some type of oil leak somewhere. This can be caused by low oil levels or not having changed your vehicle’s oil in a while. 

Engine Noise

Most normal vehicles have fairly quiet engines. Despite this, they still make noise, and metal on metal grinding or tapping noises are usually a sign that your oil needs to be changed.

The lubrication that new oil provides should cause components to easily slide over the surfaces they were designed to slide over or through. 

Vehicle Shaking

In more extreme cases, your entire vehicle can shake during idle if it needs an oil change. This is caused by the increased friction and decreased lubricity that occurs when oil wears out.

Most people think of their engines as smooth and quiet power plants, but the inside of an engine is quite violent when it is running, and a poorly running engine can have a massive effect on the entire vehicle if it is not getting lubricated as it should.

Low Oil Pressure Light

The low oil pressure warning light is designed to alert the driver to a problem when the vehicle’s computers find an issue. This should never be ignored. Numerous things within numerous components can cause this light to come on, and one of these is low oil pressure due to a decrease in the oil’s viscosity.

Check Engine Light

The check engine light can come on for any number of reasons. It may come on with the low oil pressure warning light if there is a problem with the oil pressure. Regardless of why it comes on, it should never be ignored since it can signal that so many different issues might be occurring.

When Should You Change Your Vehicle’s Oil?

There is not a definitive answer as to when you should change a vehicle’s oil since all vehicles are different and there are so many different kinds of oils available.

It is important to always consult your owner’s manual to find out exactly how often you should change your oil and what type of oil you should use. Generally, modern vehicles recommend changing the oil every 5,000 to 7,500 miles.

Modern oils have come a long way from years ago when technology was not as advanced as it is today. Many older vehicles required 3,000-mile oil change intervals, but some of the longest oil change intervals recommended by certain manufacturers extend to 15,000 miles. This is on the extreme end of the spectrum, and most professional mechanics still advise not to go that long, even if the manufacturer says that a certain make and model can.

Other factors that can affect oil change intervals include the climate in which you live, the type of driving you typically do, and the age of your vehicle.

Final Thoughts

Several things happen when you do not change your oil. The first of which is that your oil will break down and lose its lubricating abilities.

Additionally, old oil loses its viscosity – its ability to freely flow to the places it needs to be. This can result in minor consequences like the loss of engine performance and decreased fuel efficiency.

More serious problems can arise if not addressed such as overheating and total engine failure in the most extreme cases.

Shawn Furman
I have been a vehicle hobbyist for as long as I can remember as well as a freelance writer for the past three and a half years. My clients have included Vehicle Scene, Autolist, CarGurus, and now The Vehicle Lab. In addition to my current clients, I also maintain my own blog where I am able to share my knowledge and experience through vehicle reviews, car-buying guides, how-to guides, and list articles.
The Vehicle Lab looks to cover all aspects of the automotive industry: News, Maintenance & Repair Guides, and Product Reviews
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