Car servicing: Oil by numbers

When having your car serviced or topping up your own oil you may notice that oil is assigned a rating. In most cases this will be a multi-purpose oil which is rated in the format of XW-XX. If you don't know what these numbers mean then carry on reading to find out.

Breaking down the numbers:

These numbers actually refer to the viscosity rating or grade of a motor oil. Viscosity is a measure of the oil's resistance to flow, and it is crucial for proper engine lubrication. The higher the number, the thicker and more flow resistant an oil will be. The viscosity rating is usually expressed using two numbers separated by a "W," which stands for winter.

Taking 5W-30 as an example we can break down exactly what this means:

The 5 (Winter): This number indicates the oil's viscosity in cold temperatures, particularly during winter. The lower the number, the better the oil will flow in cold conditions. In this case, the 5 suggests that the oil has a relatively low viscosity when the engine is started in cold weather. This helps ensure that the oil can flow quickly to critical engine components, providing proper lubrication during cold starts.
The 30 (Operating temperature): This number indicates the oil's viscosity normal engine temperatures. The higher the number, the thicker the oil. A higher viscosity at operating temperature provides better lubrication and protection under high-temperature conditions. The 30 in 5W-30 indicates that the oil maintains a moderate thickness at normal operating temperatures.

High performance, high viscosity:

High-performance or race cars often use higher viscosity oils for several reasons related to their advanced and demanding engine designs. The choice of oil viscosity is crucial for optimal engine performance, protection, and durability in these vehicles. Here are some reasons why high-performance cars may require higher viscosity oils during servicing and maintenance :

Tighter Engine Tolerances: High-performance engines are often designed with tighter tolerances between moving parts. A higher viscosity oil can help maintain a thicker protective film between these components, reducing friction and wear in such precision-engineered systems.
High Temperatures: High-performance engines typically generate more heat due to increased power output and faster operation. Higher viscosity oils are better equipped to withstand the elevated temperatures encountered in these engines.
Extended Performance Under Stress: High-performance cars are often driven aggressively, experiencing rapid acceleration, high speeds, and frequent high RPM operation. Higher viscosity oils provide better stability under extreme conditions and maintain their protective qualities, ensuring consistent performance.
Reduced Oil Shearing: The intense mechanical forces in high-performance engines can cause oil to shear, which means it breaks down and becomes thinner over time. Higher viscosity oils are less prone to shearing, providing more stable lubrication over the oil change interval.
Enhanced Bearing Protection: The increased loads on engine bearings in high-performance vehicles benefit from the additional cushioning effect provided by higher viscosity oils. This helps protect critical engine components from wear.
Cooling: Some high-performance engines may feature advanced cooling systems, and higher viscosity oils can aid in dissipating heat more effectively.

High mileage engines

Using a higher viscosity oil for high-mileage cars can be a good idea to consider, especially if the engine is experiencing increased wear or oil consumption. Here are some reasons why a higher viscosity oil might be recommended for high-mileage cars when it comes to servicing:

Reduced Engine Wear: High-mileage oils often contain additives designed to reduce wear and friction in older engines. Higher viscosity oils, such as 10W-40, an provide an additional layer of protection for engine components.
Seal Conditioning: Older engines may experience gasket and seal wear over time, leading to oil leaks. Some high-mileage oils include additives that help condition and rejuvenate seals, reducing the likelihood of leaks.
Viscosity Stability: High-mileage oils are formulated to maintain their viscosity over a more extended period. Higher viscosity oils are less prone to shearing, providing consistent protection for older engines.
Oil Consumption: Older engines may consume more oil due to worn piston rings or valve seals. Using a higher viscosity oil can help reduce oil consumption by providing a thicker oil film and better sealing.
Temperature Control: Higher viscosity oils can offer improved heat dissipation in older engines, which may be prone to running hotter due to wear and reduced efficiency.

When considering a higher viscosity oil for a high-mileage car, it's essential to consult the vehicle's owner's manual and follow the manufacturer's recommendations. Some engines are designed to operate optimally with specific oil viscosities, and deviating from these recommendations could have unintended consequences.

Additionally, it's a good idea to monitor the oil consumption and overall engine performance regularly. If you're unsure about the best oil for your high-mileage car, consulting with a trusted mechanic or contacting the vehicle manufacturer can provide valuable guidance based on the specific needs and condition of your vehicle.

Low viscosity alternatives:

Using low viscosity oil such as 0W-20 can offer several advantages, depending on the specific needs of your vehicle and driving conditions. Here are some reasons why your manufacturer may recommend to use low viscosity oil when servicing your vehicle.

Improved Cold-Weather Performance: As we mentioned earlier, the W in the viscosity rating stands for winter, and the first number indicates the oil's flow characteristics in cold temperatures. Low viscosity oils flow more easily in cold weather, ensuring faster lubrication during cold starts, which is beneficial for engine protection.
Better Fuel Economy: Lower viscosity oils can reduce internal engine friction, leading to improved fuel efficiency. Thinner oils require less energy to circulate through the engine, contributing to better gas mileage.
Enhanced Engine Start-Up Protection: Low viscosity oils provide better protection during engine start-up, which is a critical phase when most engine wear occurs. They flow quickly to critical engine components, ensuring prompt lubrication and reducing wear.
Reduced Friction and Heat Generation: Low viscosity oils can help reduce friction and heat generation within the engine. This can contribute to overall engine health and longevity.
Compliance with Emission Standards: Many low viscosity oils are formulated to meet emission standards by reducing friction and improving engine efficiency. This can be particularly relevant in areas with stringent environmental regulations such as the UK where irregular emissions can cause a vehicle to fail its MOT test.

It's important to note that the choice of oil viscosity should align with the recommendations provided by your vehicle's manufacturer. The owner's manual will specify the recommended oil viscosity for your specific make and model, taking into account the engine design, operating conditions, and performance requirements. Always follow these recommendations for optimal engine performance and longevity.

We hope that you found this blog post useful and are always happy to help at E&J Jarvis ltd used car sales and service centre