The Hidden Costs of Using the Wrong Engine Oil

18 Dec 2024

What might seem like a trivial mistake - using the wrong engine oil - can have remarkably far-reaching consequences. The results can be anything from reduced fuel efficiency to long-term damage to components. Oil that isn’t suited to your engine’s requirements impacts your vehicle’s performance and can incur hidden costs that may not be immediately apparent. Here is a comprehensive guide to what happens if you use the wrong oil in your car. 

Can Engine Oil Affect Fuel Consumption?

Engine oil has a direct impact on fuel consumption. An oil that is right for your vehicle will be able to properly lubricate, protect, and cool the engine in all temperatures and environmental conditions. The engine will be able to pump the oil to where it is needed with ease, maximising fuel efficiency.

Does Using the Wrong Oil Increase Wear and Tear?

Oil that is not suited to your engine’s requirements can’t provide optimal lubrication and so will accelerate wear and tear of components. Too thin and the protective barrier it provides will be insufficient, allowing engine parts to grind against each other. Too thick and it might not flow adequately to cover the moving parts as needed. Both situations lead to wear on engine components like cylinders, bearings, and crankshafts, causing them to deteriorate and break, leading to costly repairs.

How Is Engine Oil Viscosity Rated?

Oil viscosity is rated by two numbers; the -W rating or winter rating denotes how well it flows in cold temperatures. The second number indicates its viscosity or thickness at high heat, such as normal engine operating temperatures. The higher the number, the thicker it is in the given conditions. For example, a 5W-20 oil will be thinner in both hot and cold conditions than a 10W-40 oil.

What Happens if I Use the Wrong Oil Viscosity?

Oil that is too thick or viscous for the climate you are driving in will fail to flow properly. Heat won’t be adequately dissipated, excess friction will be generated, and moving parts won’t be able to move smoothly. The engine will have to work harder to compensate for the excess friction, and so more fuel will be used. 

Too thin an oil, one with too low a viscosity, won’t be able to provide sufficient protection or lubrication to the engine’s components. Particularly in hotter conditions, and when the engine is up to normal operating temperature, the protective barrier offered by the oil thins. This means moving parts within the engine will rub against each other, causing wear-and-tear and metal-on-metal friction. The end result is excess heat, the engine having to work harder, and accelerated component degradation.

What happens if I use 10W-40 instead of 5W-30?

Using 10W-40 instead of 5W-30 oil means the engine will need more effort to pump the thicker oil, especially at lower temperatures. In colder conditions, this could cause harder starts and increased fuel consumption during startup, as the engine experiences more friction before the oil fully circulates. Like using 10W-30 instead of 5W-30, you may notice cold starts become more challenging.

Once the engine reaches operating temperature or in warmer weather, 10W-40 oil provides a thicker lubricating layer than 5W-30, which may offer extra protection but will also consume slightly more fuel. The result is similar to what occurs if you use 5W-40 instead of 5W-30—fuel efficiency decreases marginally due to the increased load. In extremely low temperatures, however, this thicker oil might struggle to flow, which could lead to accelerated wear over time as parts are insufficiently lubricated on startup.

These same principles apply when using 5W-30 instead of 5W-20. Although the difference is less pronounced, the slightly thicker oil can still increase fuel consumption and create minor resistance during cold starts.

Can the Wrong Engine Oil Cause Overheating?

Too thick, too thin, insufficient, and dirty engine oil can all result in your engine overheating. Too thick and your engine will struggle to pump it around the system; too thin, dirty, and low levels of oil result in friction between moving parts. The end result of all these is increased heat within your engine. 

Besides lubrication, oil is responsible for transferring heat from within the engine, dissipating it into the air. Incorrect and dirty oil and insufficient oil levels will impede this process, also resulting in excess heat build-up.  

The consequences of an engine overheating are far-reaching - reduced power and fuel efficiency are just the beginning. If the problem is severe, it can cause cracks in the engine block, transmission damage, and even total engine failure. Repairing these and replacing damaged engine parts can be extremely costly - certainly something that is best avoided. Using oil that is recommended for your car’s engine and regular oil changes are the best ways to avoid these problems. 

Does It Matter if I Use Conventional or Synthetic Oil?

Conventional mineral oil might be cheaper to purchase, but it will typically offer less protection or other benefits than a synthetic oil. Mineral oil will need more frequent changes, resulting in increased costs for maintenance long-term, too. A synthetic oil will cost more, but the advantages it offers over conventional oil are considerable.

Synthetic oil typically offers increased protection for the engine, and will be formulated to resist degradation for longer. This means it needs changing less frequently, too, resulting in reduced maintenance needs. High-quality synthetic oils often contain additives that reduce sludge build-up, resist oxidation, help keep your engine clean, and reduce emissions, even in extreme conditions. They are typically recommended for most modern and high-performance vehicles for these reasons.

What Are the Lesser Known Hidden Costs of Using the Wrong Engine Oil?

• Sludgy Deposits

Incorrect engine oil will typically break down faster, causing a build-up of sludgy deposits within the engine. If these accumulate, they can cause blockages and reduce oil further, leading to component breakdown and overheating. Clearing out these deposits is a costly process, but failing to do so can eventually mean a total engine replacement is necessary.

• Increased Emissions

The wrong oil can also result in incomplete fuel combustion, increasing engine emissions and releasing pollutants into the atmosphere. The catalytic converter may eventually clog up as a result needing replacing. In areas with strict environmental laws, driving a car with high emissions can even result in fines and legal penalties.

• Voided Warranty

Most manufacturers give explicit guidelines as to what oil types and viscosities should be used in their engines. Failure to comply with these will usually void your warranty, meaning you would have to fund costly repairs that would ordinarily be covered by the manufacturer. It is important to check and comply with these recommendations to keep your warranty intact and avoid unforeseen and unnecessary costs.

Using the wrong engine oil may be cheaper or more convenient short term, but the hidden costs can be enormous. From reduced fuel economy to engine failure, the consequences can quickly mount up. Carefully checking the manufacturer’s recommendations and selecting a high-quality oil designed for your engine will not only optimise your vehicle’s performance and longevity. It will also help protect your wallet and the environment for many years to come. 

Gulf Oil are experts in all things engine oil - for advice on choosing the right oil for your vehicle or any other related topics, contact us today.