Do High-Mileage Engines Need Thicker Oil?(Yes! 5 Reasons)

Do High-Mileage Engines Need Thicker Oil?

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Do High-Mileage Engines Need Thicker Oil?

There are diverse opinions regarding high-mileage oils. One of the schools of thought is to switch to high mileage oils when your car hits 75 000 miles.

Another school of thought is to switch to high mileage oils when your older vehicle is beginning to age or shows signs of engine loosening.

But if you notice an oil drip, this is the right time to start using high-mileage engine oil.

Additionally, when your engine “sounds louder” or you see a new rattling noise, your engine might benefit from denser oil.

But you might be asking, do high-mileage engines need thicker oil?

Yes. High mileage engines will need thicker oils.Thicker oils have additives such as conditioners, antioxidants, seal swells, detergents and friction additives that are engineered to take care of high-mileage engines. Gaskets, seals, and non-metal parts start decaying as an engine ages. This is where thicker oils come in.

This is due to using a viscosity modifier that scarcely loses viscosity quickly. Over time, all mechanical devices including, door handles, begin to loosen.

Their formulation with seal conditioners makes this possible, increasing flexibility and restoring shape. This is handy in preventing leaks in the long run.

But before you switch to thicker oils, you need to make sure that your warranty is expired. This is because using un-recommended oils in your engine will void your warranty.

Does Engine Oil Get Thicker Or Thinner With Age?

It depends on what it’s doing as it ages. Technically, the engine oil will not get thinner or thicker as it ages. By default, oil that is being used (engine is running) will get thicker.

Oil is bad by two means; first, as oil runs the engine, the long chains will be broken down due to wear. Fortunately, modern oils will last thousands of miles (10-20K).

And that’s good old conventional oil. Modern synthetic oils have beautiful properties, making them last twice as much. This will translate to anywhere around 50,000 miles.

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On the other hand, oil gets dirty. Tiny particles of combustion products and soot, as well as small insects,debris, water, and schmutz, accumulate in your oil storage “area.”

A good oil filter like Oberg will filter down to 5 microns and require frequent cleanings. But such filters are used in racing cars and special applications.

Some of the dirt is abrasive, and none is useful. No matter how expensive your oil is, if it has particles, it will hurt your engine.

Oil will not get dirty (and thicker) when not in use. Therefore, I find this question a little bit disturbing. Oil will not get thinner or thicker with age.

Is 20W50 Good For High Mileage?

No, 20W 50 is good for racing cars but not for high-mileage cars. As you might know, an engine requires oil to run smoothly, which lubricates the moving parts.

Consequently, correct oil viscosity and levels are required within an engine chamber to ensure that the engine is well lubricated and cooled.

While newer engines will benefit from thinner oils, older engines will be better off with thicker oils. This is handy in the prevention of friction and oil loss.

Since the efficiency of any oil is primarily based on its viscosity;

It would be fair if we first look at the viscosity of engine oil 20W50 before we continue disqualifying it from high mileage use.

Indeed, engine oil 20W50’s (Amazon Link) viscosity is geared toward racing engines.

On the other hand, high-mileage engines run extremely hot, requiring heavy load operation and making 20W 50 unsuitable for use on such engines.

This kind of thickness is not meant for daily, older vehicle use.

If 20W 50 is used in high-mileage vehicles, its excellent viscosity will drag down the functioning of the crankshaft and result in lower horsepower.

When Should You Use 20W50 Oil?

20W50 motor oil is the oil required to be used in warmer climates. It’s largely understood that warmer temperatures cause oil to thin.

Therefore, due to its thickness, 20W50 becomes the go-to-oil for vehicles subjected to hot temperatures and those used in high-stress activities like hauling and pulling trailers.

As I have severally insinuated, 20W50 motor oil is high viscosity oil, providing cushioning and protection against metal-to-metal contact.

It also comes as an appropriate and effective sealant, better when compared to thinner oils. These are some of the benefits that will extend your engine life.

But 20W50 is not for all vehicles. Indeed, 20W50 is recommended for a particular type of vehicle.

These include large or small diesel engines, motorcycles, gasoline engines, and aviation vehicles. 20W50 is also well-suited for both air- and liquid-cooled engines.

Due to the number and variety of motor oils in the market, something simple as motor oil can be quite confusing.

Added to the fact that there are multitudes of oil types, different brands for specific applications complicate the situation further.

It’s scary to imagine that you can damage your engine by the use of the wrong oil.

Unfortunately, different brands use similar numeric characters, making it extremely difficult to distinguish or identify them.

Is 10W30 Thicker Than 10W40?

No,10W30 is not thicker than 10W40 since the latter is thicker at operating/high temperatures. Thickness is the significant difference between 10W30 and 10W40.

When you look at the first viscosity number, “10”, you will appreciate that these oils have the same viscosity at low temperatures.

This is primarily the case when starting the engine during winter. The higher this number is, the harder it pours when cold.

So, so an oil rated “10” will run slower than one rated “5.”

However, the second number for these two oils is different. And this is the number that shows the rating for ease of flow at operating temperatures or in hot weather.

In our case, this number is “30” and “40” for the two oils. The lower this number is, the poorer it adheres to and protects components under extreme pressure and heat.

Should I Use 10w30 Or 10w40?

When it comes to which oil you should choose between 10W30 and 10W40, it will depend on several issues.

First, a key aspect that you will need to adhere to is the rating specified by your engine’s manufacturer. This is the only way you will guarantee proper lubrication.

In this case, you may not compare the two and say a particular one operates better than the other since each engine has its specific rating.  

However, you might find that some manufacturers provide a range of viscosities, and this is where you might be free to compare these two types of oil.

This brings us to the second factor to consider; your driving conditions.

If you are driving in cold weather, you might find the use of 10w30 oil to be better since it helps in the reduction of excessive oil temperatures and drag as your engine warms up.

Using 10w40 oil(Amazon Link) in the summer will be more beneficial since it helps the oil stick to the internal components in high temperatures.

This will be useful in preventing wear and tear with regard to metal-to-metal contact between moving parts.

As you might remember, I mentioned that 10w30 and 10w40 oil differ only in their thickness at engine operating (hot) temperatures.

The viscosity is the same during a cold startup as the starting viscosity is “10” for both formulations.

Does High Mileage Oil Work?

Yes, high mileage oil is worth it. Made from a blend of synthetic and petroleum-based oils, high-mileage oils are a bit pricier per quart than conventional motor oils.

Like any other mechanical machine, a motor vehicle’s components should deteriorate and wear out over time.

When you drive your car over the thousands of miles, a toll is exacted on some parts of the engine including, rod bearing connections, valve seals, piston rings, and the crankshaft.

Over time, all engine parts will develop some slop and wastage.

Indeed, deteriorated connections, worn-out seals, and sludge buildups are the most common problems in high-mileage engines. And here is where high-mileage oil comes in handy.

The design of high-mileage oils is for helping engines that have been driven for over 75k to 100k miles on the odometer.

Such oils come with additive packages that will benefit an old engine. High-mileage oils are handy in regenerating the gaskets and swelling the seals back to their previous shape.

This is good as it seals any engine leaks. The seal conditioners in the oil do such repairs. Again, high mileage oils keep the oil thicker due to the viscosity modifiers in them.

In addition to this, this king of oils reduces sludge and carbon buildup due to the detergent elements.

High-mileage oils reduce friction by using modifiers, helping make up for the lost internal tolerances between parts in motion.

Still, high-mileage oils are known to prevent corrosion in internal parts since the additive packages also consist of anti-corrosion agents.

What Will Happen If I Use 10W40 Instead Of 10W30?

Some say that swapping 10W30 with 10W40 is fine if you don’t live in freezing weather. This is not necessarily true.

It’s indisputable that 10W40 is more viscous than 10W30 at high temperatures. This is clear from the basic fact that “40” is more significant than “30.”

But if you put 10W40 engine oil in an engine designed for 10W30 engine oil, the “thicker” oil would occasion friction in the engine.

Do High-Mileage Engines Need Thicker Oil?

This will also result in an increased load on the oil pump. This will lead to more fuel consumption, a drop in performance, and a potential engine knock shortly.

Is 10W40 Synthetic?

No, not exactly. 10w40 motor oil is one of the semi-synthetic motor oils available in the market today.

The 10W40 has a viscosity of 10 and 40 in low temperatures and higher temperatures, respectively.

Compared with 5W30, another popular and commonly used oil, 10W40, is more viscous.

Like a 10W40, synthetic oils have crude oil as their base but are subjected to more complex processing down to the molecular level.

Consequently, synthetic oils will give better wear control, deposit control, viscosity, and low-temperature fluidity.

If you combine all these benefits, it’s not hard to realize that it’s better to use synthetic oil rather than semi-synthetic oil.

Indeed, synthetic oil will reduce the risk of equipment failure, extending its service life by a more significant margin than a semi-synthetic oil.

What Is The Difference Between 20w 40 And 20w 50?

Regarding choosing the best engine oil suited for your car, there are a couple of things you need to consider. One of such things is engine oil grades.

Engine oils have standards that come in handy in helping us check the viscosity of a lubricant at specific temperatures.

Such information is handy in determining whether a particular engine oil will work smoothly and efficiently in a specific environment.

But these aspects of such standards can seem confusing, like using a 20w40 or 20w50 engine oil for your car.

Just that you can be sure, you need to note that the oil will flow better and more efficiently at low numbers.

Comparing 20W40 and 20W50 oils requires us to look at their operation in high temperatures since their viscosity is the same in low temperatures or at engine startup.

20W-40 is a multi-grade oil that will operate in both hotter and colder conditions. It’s both a diesel and a petrol engine oil, making it a lucrative option to choose from.

20W40 has superior performance, better thermal stability, high viscosity, anti-wear qualities, a good cleaning capacity, and high clutch friction properties.

On the other hand, 20W50 is still a muti-viscosity oil. However, it’s thicker and more viscous, outperforming its counterpart in hotter temperatures and warmer climates.

This is the only oil that will not thin out in these temperatures.

Can I Use SAE 30 Instead Of 10W30?

When it comes to comparing SAE 30 and 10W30, there are things that you need to think about.

While the two oils might seem similar, they have differences that you need to consider when deciding which between the two you want to use.

As you can see, SAE 30 has only one number, meaning it’s a mono-grade oil. But 10W30 is a multi-grade as it has two numbers.

Mono-grade oils operate best at high temperatures. If there is a significant temperature drop, the oil will thicken and hinder its effectiveness.

On the other hand, 10W30 is a blended oil with two numbers, one for hot weather and cold weather.

This is an oil that will operate in a wide range of temperatures, making it better.

So, if your engine has a rating of 10W30, it’s not advisable to use SAE30 unless you are in a hot temperature region.


High mileage engines need thicker oil to seal any leaks and improve performance.

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