Engine oils are essential for keeping an engine running, and 10W-40 engine oil is fairly common with engines that rev highly and use some form of compression. Most modern car engines are fairly small and use turbochargers to help the engine breathe a tad more cleanly and optimise extra power.
Essentially, 10W-40 oil caters to engines that are likely to be busier than larger, low-stress units. In other words, they’re for most engines you see in everyday cars.
Whether it’s regular car oil or the four-stroke version, engine oil changes are also essential to keeping your vehicle running. When you take your car in for its annual service, an oil and filter change is at the top of the mechanic’s priority. This is purely to ensure your engine is lubricated using fresh, clean oil and won’t ever sludge. Sludging of oils in an engine can spell bad news for the heart of your vehicle.
The best 10W-40 engine oil at a glance:
Editor’s pick: Mobil Super 2000 Semi Synthetic Oil, 5L – Buy from Amazon.
Best for preventing sludge: Castrol GTX Ultraclean, 5L – Buy from Amazon.
Best for seal protection: Liqui Moly Super Leichtlauf – Buy from Amazon.
Choosing the right 10W-40 oil for your car is a little trickier than it looks. They are thicker than 5W-30 engine oils and are designed to withstand higher temperatures. Loads of top brands are competing for your money, so we’ve made it easier and compiled a shortlist.
How to find the right maintenance parts for your car
Pros
- Easy to suss out the correct bits
- You can save your vehicle for future searches
Cons
- You need prime for free delivery
The best 10W-40 engine oil
Editor's pick
It provides high temperature protection, supports the engine when cold, and helps maintain its cleanliness. Mobil recommends that its semi synthetic products are best used in cars with over 75,000 miles, so it's safe to say your daily commuter could benefit highly from them.
Pros
- Great for high mileage cars
- Provides ample protection against sludge
Cons
- Full synthetics are more protective
Best 10W40 oil for preventing sludge
The 3X-Clean is designed to deal with the three main causes of engine sludge: short trips, contaminants, and heat. Ideally, an engine is at its healthiest when you warm it up to temperature, give it a good run and let it cool down a bit. Shorter trips aren't kind to that formula, and Castrol's GTX range is designed to tackle it.
Pros
- Highly effective at cleaning, thanks to additives
- Protects against sludge
Cons
- A synthetic would be slightly better for higher mileage cars
Best 10W40 oil for urban driving
It's suitable not only for both petrol and diesel engines, but will also support engines that run on biodiesel and petrol with ethanol blends.
Pros
- Very adaptable for different fuel types
- Great for urban driving
Cons
- Not as protective as full synthetics
Best 10W40 oil for seal protection
This ensures low oil consumption and is particularly beneficial at cleaning and dirt suspending. It's part-synthetic too, which only adds to the oil's durability.
Pros
- Excellent wear protection
- Low oil consumption when in use
Cons
- Overkill for newer engines
Best 10W40 oil for cold starts
It all helps maintain the longevity of your engine, and Castrol says the oil clings onto the surfaces like a magnet, ensuring full lubrication even on cold starts.
Pros
- Very effective lubrication and protection
- Fights against common engine wear causes
Cons
- No use of synthetics
FAQs
What makes 10W-40 engine oil different from the others?
To make things ultra simple, the main number you see on engine oils denotes the viscosity at low and high temperatures. The first number is the low viscosity rating in cold temperatures (W standing for winter). This is followed followed by the high viscosity, which is related to high temperatures. So, 10W-40 oil is thicker than 5W-30. And whilst thicker on cold start-ups, 10W-40 will provide more ample protection when the engine is warm and hot. The same viscosity measurements apply when it comes to synthetic engine oils, too.
The viscosity itself is measures by its flow resistance. The numbers relate to how well the oil flows when it’s hot and cold. But it’s important to note that the second number is a measurement of how well the oil flows at normal operating temperatures. So, 0W-20 oil is very thin, and 15W-50 is very thick. When engines get very hot and are closer to the risk of overheating, don’t rely on the engine oil to help you out. With gearbox oils, they tend to be more manufacturer and gearbox-specific, so make sure to do your research before buying.
We briefly mentioned synthetic oil as well throughout the product selections. Whether it’s part or fully synthetic, they’re not 100% oil and use a number of additives and non-oil solutions to lubricate the engine. For cars with higher mileages, they can be greatly beneficial to protecting seals and important components.
What is 10W-40 oil recommended for?
10W-40 oil is commonly recommended for older vehicles or those with high mileage, as well as for engines operating under high-temperature conditions. It provides good protection and lubrication for a wide range of temperatures.
Is 10W-40 oil good or bad?
10W-40 oil is generally considered good when used in the right engine. It provides excellent protection and performance in appropriate conditions. However, it may not be suitable for newer engines designed for lower viscosity oils.
Is there 10W-40 that is fully synthetic?
Yes, there are fully synthetic 10W-40 oils available on the market. These offer enhanced performance and protection compared to conventional or semi-synthetic oils.
Is it bad to put 10W-40 in a 5W-30?
Using 10W-40 oil in an engine designed for 5W-30 can be problematic. It may lead to reduced fuel efficiency and potentially inadequate lubrication, particularly at lower temperatures. Always follow the manufacturer’s recommendations for oil viscosity.
How long does 10W-40 oil last?
The longevity of 10W-40 oil depends on several factors, including driving conditions and engine type. Typically, it should be changed every 5,000 to 7,500 miles or every six months, whichever comes first. Always refer to the vehicle’s owner manual for specific guidance.
Is 10W-40 the thickest oil?
No, 10W-40 is not the thickest oil. There are oils with higher viscosity ratings, such as 20W-50, which are thicker. The viscosity rating indicates the oil’s flow characteristics at different temperatures.
How we choose
All of these 10W-40 engine oils have been hand-selected by our team of experts who have spent hours investigating and researching 10W-40 engine oils to make it easier for you to find the very best, and we’d never recommend a product we don’t believe in.
Where possible, we also test and share the latest and best products you should know about.
Aaron Hussain is a commercial content writer at Bauer Media writing for Parkers and CAR. He is obsessed with classic cars and anything with a fascinating story to tell.
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