10W40 vs. 5W30: What Happens If I Use the Wrong Motor Oil?

Like most people, you probably don’t think about motor oil all that often. But it’s an important topic, especially if you want to keep your car running well for as long as possible. 

What happens if I use 10W40 instead of 5w40? The difference between 10w40 and 5W-5 is only noticeable when cold, but at the operating temperature, they are the same. 

Multi viscosity oils with lower W numbers have been specifically designed to flow better in very low temperatures to provide more protection for your engine’s internals during those cooler months ahead.

There is no need to use a 5w-40 if the vehicle only requires a 10w-40. Using a 5w-40 instead of a 10W depends on how much you need to cool your engine. 

If it’s just ten degrees warmer, stick with what has been working for a while and get more out by adding fewer liquids; but if it’s hot enough, those few dollars will buy twice as much capability in relief.

You can use 5w-40 anywhere; a 10w-40 is recommended. 5w-40 and 10w 40 share the same properties, so you can use either anywhere; a higher quality oil is recommended. 

At operating temperatures, both oils will be 40wt, but there’s an important difference between them when it comes to viscosity – 5 weight “5W” stands for colder temps while 10 W stand means warmer ones!

The 5-40 is thicker than the 40, but not by as much. When it comes to colder temperatures, both oils are far more sluggish and difficult for them to flow properly, resulting in a slightly reduced ability on their part when considering how well they operate efficiently within these conditions.

5W-40 motor oil is commonly made from synthetic, while a 10w 40 might be Petroleum-based with lots of VII (viscosity index improver) and shears down to 30wt or even 20 wt over time. 

The less sheering down will happen in this case because it’s also Petroleum-based, which means its VI number could potentially increase by 1 level when exposed to high temperatures like those found on an engine dyno sheet.

Also Read: Can I use 10W40 instead of 20w40? here’s why

Is it OK to use 10W40 instead of 5W30?

Use the oil viscosity that your manufacturer recommends. If they recommend 10–40, then stick with it.

However, the viscosity of the oilOpens in a new tab. you use changes depending on whether or not your car will be driving in extreme conditions. For example, if it’s very cold outside and snow banks alongside roads, a thinner fluid would be needed to avoid clogs from forming. 

Because these oils don’t flow as well at low temperatures, they’ll stay where they’re put without flowing around objects inside them easily enough.

The opposite applies when things get too hot–the higher temperature means more volatile molecules exist within automotive fluids, so whatever kind is currently being used won’t remain stuck together.

As you can see, 10w-40 is a good standard for most of the temperatures we experience. This includes -25C to 40°C, with 5W 30 being an alternative if your car goes below that range or you prefer more thick oil in colder climates where it’s needed!

Using old-fashioned straight-weight oil in a modern engine may be the worst thing you can do for your car. 

Modern engines need a specific type of motor oils, and those at the top Combine this chart shows how to properly maintain them with 30 or 15-watt ratings depending on what manufacturer’s recommendations are followed closely so that cars running all day smoothly long don’t end up backfiring while burning out before their time.

Also Read:Is It OK To Use 10W40 Instead of 10W30? here’s why

Can 5W-40 oil harm the engine?

Under normal conditions, going to a 5w-40 version of an approved oil won’t hurt your engine. 

But if you regularly drive in hot weather above 35 degrees Celsius (95 °F), the more expensive and thicker 10W50 may be better for preventing breakdowns on extended trips or high mileages.

Because they resist evaporating at higher temperatures before reaching their full capacity, there is less risk than other oils with lower boiling points like 5W30.

The American Petroleum Institute (API) service level measures how well an oil company maintains its equipment and facilities. The higher number means they do more thorough testing, which leads to better quality products for you.

A letter grade indicates the recommended service level for your engine care product. The higher the SL, SN, or other second-letter grades on an oil upgrade, the more recent and better quality than older upgrades with lower numbers in this category.

Diesel engines have their standards, and it’s important to know the difference between them. For example, if your car manufacturer recommends using API Service SL for cars with diesel fuel, then you should use SN instead- but not SH.

Will 5W40 cause any harm?

A lot goes into deciding which engine oil you should use, and it depends on things like the general ambient temperature and design parameters, such as whether or not there’s some sort of restriction for your vehicle. 

For example, 5W-40 would be used in colder environments where 10w140 would wear more easily because they’re heavier oils!

The vehicle or engine manufacturer’s recommended oil viscosity is the only one you should use. Alternative oils may have different characteristics that could affect your car, so check with a professional before making any changes.

What does 5w40 mean?

The “W” stands for winter and designates the oil’s thickness at low temperatures. The number preceding this letter indicates how thick or fluid-like an oil will be in cold weather conditions.

Why does the viscosity of motor oil matter?

Oil viscosity is a crucial factor in maintaining engine performance. The wrong type of oil can lead to sluggishness and excessive wear, while the right kind will provide better fuel efficiency by keeping moving parts protected from damage.

Maintaining an optimal temperature helps keep your car running smoothly all year long.

Oil viscosity can have a significant effect on engine performance. A thicker, more viscous oil will do better at protecting components and helping your car run smoothly. 

Still, too much of it may confuse enthusiasts who want maximum efficiency from their vehicle.

5W40 vs. 10W40 – Differences

The 5W40 is thinner than the 10w 40 at lower temperatures, but both oils perform their intended functions equally well when it comes to high-temperature use.

The 5W40 motor oil is a great choice for any vehicle that requires frequent starts and stops. It flows easily, making it easy on all your engine’s moving parts- especially when you need to start-up or shut down quickly.

10W40 Motor Oil Characteristics

The 10W40 motor oil is thicker than 5w 40 but a little bit thinner in comparison. This means that it will work perfectly well for all moving parts during the start-up and running of your motorcycle’s engine without ever experiencing sludge or viscosity issues.

5W40 Motor Oil Characteristics

The 5W40 is thinner than the 10-weight 40, which means it can get into most parts of your engine and provide some initial lubrication for when you start up.

The 40 indicates that this engine oil has a thicker consistency than most motor oils. The 5W-40 is just below what you consider “normal” thickness and provides better protection for your car or truck’s components against wear caused by friction.

Can I mix 5W40 and 10W40?

The 5W-40 and 10W– 40 share a similar API rating, so you’ll want to ensure that your engine’s oil capacity is enough for both. If it isn’t, then don’t worry! The small remainder of the previous grade will mix in with this new one when adding more.

Also Read: Is 10w40 oil thicker than 20w50? Do They Have the Same Effect?

Is 10w40 good for high mileage?

If you own a high mileage vehicle and are unsure what type of motor oil to use, Mobil 1 High Mileage 10W-40 is a perfect choice. ExxonMobil has recommended this product for those who drive cars or trucks with higher miles on their odometers than usually seen in an average lifetime.

The best way to keep your car running smoothly and efficiently is with the help of Mobil 1 High Mileage 10W40 motor oil. 

This special blend was designed for high mileage vehicles, so you can be confident knowing that it will provide maximum protection against wear during tough times when driving on dirt roads or urban streets.

Mobil 1 High Mileage 10W-40 is the best overall choice for your vehicle, meeting or exceeding tough industry standards. It protects against wear and sludge while providing excellent lubrication to help you get more out of life with every mile driven.

Advantages of 10W-40

  • Extend engine life
  • Clean up engine sludge with active cleaning agents
  • Prevent leaks
  • Unsurpassed wear protection
  • Protects for up to 10,000 miles between oil changes
  • Designed to clean up sludge left behind in your engine
  • Exceptional overall engine protection to help extend engine life


  • Active cleaning agents
  • Outstanding thermal and oxidation stability
  • Advanced Full synthetic formula
  • Precise balance of performance additives

Jim Harmer

I am Jim Harmer and I am in love with the outdoors. I share all the information I know on all activities I like doing in my home in this website. You are welcome to read and reach out for more information.

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