Synthetic oil is used to help your engine run better. The main use of oil in an engine is to prevent friction. It prevents metal-to-metal contact, which also reduces heat. Oil isolates and suspends harmful contaminants between oil changes. By suspending these particles, every oil change flushes this damaging material out of the engine.
Oil also protects against rust and corrosion by coating all internal engine parts, which prevents oxidation. We’ll show you the best 5w40 synthetic oil for your car.
Best 5w40 Synthetic Oils – Quick Look on Our Top Picks
How does the lubrication system in a car work?
A lubrication system uses a positive-displacement oil pump to pressurize engine oil passage. Some pumps mount at the front of the crankshaft while other engines drive the pump using a chain connected to the crankshaft. The pump assembly includes a relief valve designed to limit total system pressure. The relief valve opens if oil pressure exceeds spring pressure due to extremely low temperatures or a blockage in the oil passages. When open, the relief valve directs oil back to the oil pan.
From the oil pump assembly, oil flows to an oil filter. Inside, filtration media traps contaminants such as dirt or metal particles. If allowed to circulate in the oil system, these contaminants can cause wear on the bearing surfaces of the engine. Contaminants may be the product of combustion or an internal contaminant. Products of combustion include soot, carbon particles, unburned fuel, and water. Internal contaminants consist of metallic particles, spent oil additives, sulfuric acid, and nitric acid. These contaminants increase wear on moving parts, which can lead to greater friction, reduced oil pressure, and component failure. Some contaminants can plug the media inside the oil filter.
While the oil filter removes solid contaminants from the engine crankcase, the positive crankcase ventilation, or PCV system, removes gaseous contaminants. These contaminants include water vapor formed through condensation and combustion gases that leak past the piston rings. The PCV system sucks in filtered air and uses a vacuum to send the crankcase vapors into the combustion chamber. This helps to reduce sludge formation and also increases the engine’s oil life.
Some engines use an engine oil cooler at the filter to transfer heat into the cooling system. One coolant line delivers coolant to the oil cooler, while a second line sends the coolant and heat into the engine water jacket.
From the oil filter, engine oil travels through oil passages. Most oil passages end at a bearing. Bearings typically include a wear surface on the rotating component and a bearing surface. The bearing surface may be a machined surface on the component or a replaceable bearing shell. Between the two components, a tiny gap allows a narrow film of oil to isolate the parts. To deliver oil to this gap, bearings include a hole in their face.
From this delivery point, oil fills the space between the shaft and bearing. From there oil drains from the bearing edge and returns to the oil pan. As the oil flows from the friction surface, it removes heat and impurities.
What is the difference between synthetic and mineral oils?
The differences start with how they’re made.
Mineral oils originate from crude oil extracted from the earth. They then go through a refining process to have their impurities removed.
Synthetic oils also originate from crude oil but are then put through chemical reaction processes in a factory, and are specially engineered to withstand and perform under extreme temperatures.
Synthetic oils flow more easily at startup, last longer, and provide better protection and performance. This means mineral oils and synthetic oils perform differently in a hot engine. Think of mineral oil as butter. If you put it on a hot frying pan, you’ll notice that the butter starts smoking, burning, and leave a cooking deposit. It doesn’t last very long and does not hold up well under high temperatures.
Synthetic oil, on the other hand, is like vegetable oil. Under the same temperatures and conditions, it doesn’t smoke or burn up and keeps the pan coated. Even more, it can withstand even higher temperatures while still providing the same protection. Like frying pans, engines can generate a lot of heat, so what would you rather have in your engines under extremely hot conditions? Synthetic oil or mineral oil?
Choosing a good synthetic oil for your car
Choosing a good motor oil for your car might seem like a daunting task. Just check out the oil shelves at any store and there are dozens of options to choose from. However, narrowing down your options is easy. Just take a look at your car’s owner manual. It will let you know the best type of oil to use. Once you have that, the next step is to select a good oil brand.
Best 5w40 Synthetic Oils – TOP 5
Valvoline SynPower Full Synthetic Motor Oil, SAE 5W-40 MST
Dr. John Ellis founded Valvoline many years ago. But did you know that he is also credited as being the one who actually invented motor oil? Valvoline is now ranked as one of the largest producers of motor oil in the United States and has sponsored all sorts of NASCAR and NHRA events.
This Valvoline SynPower Full Synthetic Motor Oil has additives that provide sludge and varnish protection. It can be used under severe driving conditions, either in cold or warm environments, and it will help maintain fuel efficiency. Most of VW, Audi, Mercedes and BMW’s specifications are met or exceeded by this oil. It is classified as a fully synthetic oil, meaning that no crude oil has been involved in making it.
- Accepted by most of the top car brands
- Low ash content, which reduces sulfated ash, phosphorus, and sulfur deposits
- Good for RV use—handles the abuse without issues
- On rare occasions, the seal on the bottle might be loose, and oil can leak out
Check Price on Amazon
Mercedes-Benz MB229.51 Approved Ardeca Synth-XL 5w-40 Fully Synthetic Motor Oil
The Ardeca Synth-XL 5w-40 is a fully synthetic oil with a mid-SAPS formula. SAPS is sulfated ash, phosphorus, and sulfur, and using mid-SAPS oil is required under Euro 4 and Euro 5 norms. This oil is fully backward compatible so that you can use it for engines of previous generations, such as the Euro 1,2, or 3. It can be used on petrol and diesel engines and provides excellent oxidation resistance, very high thermal stability, and a very low resistance at start.
If your car uses one of the latest di-engines with pump-injector units, this oil might be a good option. It provides high protection of the exhaust catalyst.
- Meets recommendations for Mercedes diesel engines
- Meets VW 505.01 specifications
- Good option for latest generation petrol cars
- Compared to other synthetic oils, it can be pricier
Check Price on Amazon
Pentosin 8042206 Pento High-Performance II 5W-40 Synthetic Motor Oil
Pentosin is a brand used by many in the automotive industry. This is a newly formulated, fully synthetic oil and is considered a 4-season oil, which means it can be used in vehicles for all-year use.
The formula used to make this oil allows for longer changing intervals and contains special friction modifiers. These help your car’s engine run smoothly and improves fuel economy. It also preserves the catalyst and provides top engine lubrication protection, and reduces fuel deposits motor oil sludge. Pentosin 8042206 Pento High-Performance II 5W-40 Synthetic Motor Oil can be used on gas or diesel engines.
- Excellent option if you have a TDI vehicle
- German oil for German cars. Preferred by VW and Audi owners
- Great for all seasons
- Can be used in gas or diesel engines
- Bottle seal can be hard to open
Check Price on Amazon
Shell Rotella 550019921-3PK T6 5W-40 Full Synthetic Heavy Duty Diesel Engine Oil
Shell Oil Company is among the largest oil companies in the world and has plenty of experience in everything from exploration to production and refining of petroleum products. When you purchase Shell oil, you know there is a reliable brand behind it.
Shell Rotella 550019921-3PK T6 5W-40 is fully synthetic engine oil with low-ash additive technology. It has top performances in both high and low temperatures, and its formula is designed to provide acid, deposit, and wear controls. The T6 is the most recent launch in the Rotella oil line and offers a 34% better wear performance over previous formulations. Although it can be used on older models, it is particularly effective in modern low-emission, heavy duty engines.
- JASO-MA rated, can be used even in motorcycles
- Good option for new and older vehicles
- Turbo car owners report a decrease in oil consumption after using this oil
- Some bottles are not adequately sealed and tend to leak
Check Price on Amazon
Liqui Moly 2041 Premium 5W-40 Synthetic Motor Oil
Liqui Moly is a German company founded in 1957. Although they are more recent than several of their competitors, they quickly gathered a significant number of fans and their products are now sold in 120 countries.
Liqui Moly 2041 Premium 5W-40 is a fully synthetic, all-season motor oil, which can be used in gasoline and diesel vehicles. It has been tested safe with turbochargers and catalytic converters, exceeding all major European car manufacturer’s requirements and specifications. Maintaining an optimum oil pressure under practically all operation conditions, this oil has a high shear stability and a high lubrication reliability.
- Rapid oil delivery, even at low temperatures
- Good option for high-performance cars
- The spout has a small diameter opening, can be difficult to pour
- Brand is popular in Europe, but not very well-known in America
Check Price on Amazon
Considering that Valvoline was founded by the inventor of motor oil, this is a brand with a long car-related history and one you should consider as a primary option when selecting your vehicle’s oil. The Valvoline SAE 5W-40 MST meets the latest requirements for European applications including BMW, Mercedes-Benz and BMW gasoline and diesel engines. It also meets the performance requirements of virtually all turbocharged, supercharged, and naturally aspirated cars in North America. Its deposit control, wear protection, break-down resistance, and cold-start properties make it probably the best 5w40 synthetic oil you can get.