Drivers who care for and maintain their vehicles know the importance of engine oils – and of car oil changes. They change their oil regularly according to the seasons or miles they’ve traveled, and look into different types of engine oils to find the one that gives their vehicle the best performance. And while not every driver is this particular about their engine lubricants, anyone who has sat behind a wheel or the handlebars knows that the oil needs to be changed at some point.
But what happens when you don’t change your engine oil?
To answer that question, let’s start by looking at what engine oils do, and why they’re important to the maintenance of your vehicle.
What role does engine oil play? Friction reduction and lubrication
When the engine is running, there will always be friction – especially between the pistons and the cylinder. Friction is created between the connecting rod and the crankshaft, and that’s where engine oil is needed. Engine oils most basic job is to lubricate – hence why engine oils are also called ‘lubricants.’
Engine oil works by creating a film on the inner wall of the cylinder, preventing direct contact between the pistons and the cylinder. Since oil is a liquid, it naturally flows downward over time. But as the pistons move up and down, they also pump oil back up to the rest of the cylinder, maintaining an even coverage as you drive.
Friction between the cylinder and pistons is reduced, and the rotations can happen more smoothly.
Cooling your engine and releasing heat
The second role of engine oil is cooling down your engine, though not many people realize how important engine oil is to temperature regulation. Your engine generates a massive amount of heat from fuel combustion. As engine oil moves around the inside of your engine, it carries heat away from hot spots and disperses it evenly, helping to regulate the temperature and prevent overheating.
Pistons and cylinders ay appear to be a perfect match in size, but if that were the case, they would rub against each other too much and cause friction to reach excessive levels.
To avoid this, manufacturers actually make the cylinder and pistons with a small gap in between. The engine oil then forms a layer on the engine’s inner wall to seal the gap between the cylinder and the pistons, preventing fuel from leaking through the gap. This is why engine oil viscosity is so important – an engine oil produced with the right viscosity can act as a highly effective sealant and help prevent leakages.
Washing and rust prevention
The final role of engine oil is to prevent carbon sludge and combustion residue from accumulating inside the engine, and to prevent rust. Washing is a very important job of any good engine oil, helping carry away debris that contaminates the injected fuel.
Now that we understand the role of engine oil, we can answer the most important question: what happens if you don’t change your engine oil?
Fuel efficiency starts to fall
First, lubrication inside your engine will start to drop. When lubrication starts to degrade, the fuel efficiency of your vehicle falls with it. This results in increased internal friction, which then puts more pressure on the engine and makes its job more difficult. This causes the power to drop significantly – and as the engine fights harder than usual to maintain performance, fuel efficiency suffers considerably.
Noise in the engine
If you’ve ever driven your vehicle too far past the recommended engine oil change date, you might have noticed a suspicious rattling sound coming from under the hood. This happens because unchanged engine oil doesn’t control heat levels as well as newer oil. When heat builds up inside the engine, it causes the fuel to combust at unexpected times. Engine oil plays a huge role in keeping an engine cool, second only to the coolant, so the impact of oil and past tis time engine oil in the cooling system shouldn’t be overlooked.
Leaks and seals
We already explored how engine oil can help create a seal inside your engine that prevents leakage. But old engine oil breaks down over time and can’t seal your engine as well as fresh oil. This allows certain metals to expand, ultimately causing the pistons to overwhelm the engine’s inner walls. Also, when your oil fails to act as a proper sealant, it can leave gaps inside the engine through which fuel can leak, sapping power from the engine and reducing fuel efficiency over time.
The final downside to not changing your oil frequently enough is the sheer amount of build up that will occur inside your engine. A dirty, sludge filled engine can lead to problems like contaminating the injected fuel or preventing the spark plug from igniting. Residue cleared away by the engine oil is filtered through an oil filter, but the filter can only do so much. If you drive without changing your oil for long enough, the engine oil will become black and contaminated – and so will the engine itself.
Changing engine oil regularly is crucial to healthy vehicle maintenance. When engine oil goes unchanged for too long, a host of problems can set in. Engine oil contains a important properties and additives that help with the four functions we’ve discussed so far, and when engine oil is contaminated by debris or excessive heat, function is either damaged or lost entirely.
Of course, driving your vehicle for a short time past the replacement cycle won’t cause you major problems right away. In recent years, engines have also become considerably more durable, especially in gasoline direct injection (GDI) engines, while the functions for cleaning the cylinders and cooling the engine have improved significantly. But even with today’s durable and efficient engines, going too long without changing your engine oil is a recipe for trouble, cutting engine performance over time.
So how often should engine oil be changed? The answer to this question is different for every driver, and is influenced by the driving environment, style, and how frequently you drive. Due to engine improvements, engine oil change cycles are also getting longer, with some vehicle manufacturers recommending you change the oil once every two years. It’s also important to consider the risks of overdoing it and changing your oil too much, including the cost of car oil changes, unnecessary waste, and environmental issues. While we may need to rethink engine oil cycles based on new and improved vehicles, one thing is for sure: if you want your vehicle to last for years to come, changing your oil regularly is far better than not changing it.