Can You Use 15w40 In A Gas Engine? (Know It Now!)

can you use rotella 15w40 in a gas engine

Diesel oils are top-rated among car owners due to their increased detergency characteristics than gasoline motor oils.

Can You Use 15w40 in a Gas Engine? 

You can run your gas engine using high viscosity diesel oil like 15w40, provided that the oil meets your engine’s viscosity requirements and other specifications. For instance, if your car’s gas engine requires 5w30 motor oil with the appropriate API SN specification, you can opt for diesel oil that meets the same viscosity and API SP requirements.

However, it’s worth noting that diesel oil isn’t needed for a regular gasoline engine. The best option would be 5w30, which will deliver the best value and performance. It is common for gas-powered vehicle owners to prefer diesel oils over gasoline motor oils.

What Is the Difference Between Diesel and Gasoline Engine Oil? 

Even though manufacturers use mineral oil to make both engine oils, the refining process is significantly different.

Using diesel engine oil results in better fuel efficiency and lowers CO2 emissions from your vehicle. This is because diesel engine oil contains more energy per liter than gasoline.

Many people assume that diesel oils are tougher and more durable than gasoline oils. They believe that diesel oils can withstand the high heat produced by powerful turbocharged engines.

Others prefer diesel oils like 15w40 because they have high viscosity to protect their engines from increased wear and tear. It’s also worth noting that it is usually much easier for some people to find high viscosity diesel oil like 15w40 than gasoline motor oil.

What Happens If I Use 15w40 Diesel Oil in a Gas Engine? 

  • If you use 15w40 in your gas-powered engine instead of 5w30, it will increase your fuel consumption. This is because the diesel oil will increase your gasoline engine’s crank load.
  • While the 15w40 oil won’t blow off, it will likely wear out your engine a lot faster than if you used gasoline motor oil with great cold start properties like 5w30.
  • Since diesel oil is much denser and thicker than gasoline oil, the former won’t flow through the moving parts as quickly as required. Therefore, the 15w40 will only end up clogging the fuel filter and the fuel injectors if it makes its way into the engine.

What If I Have to Use 15w40? How Should I Use It? 

You should only consider using 15w40 if you have a highly modified gas engine designed to produce more horsepower. This is because a heavily modified engine will likely need higher viscosity oil like 15w40 to handle the stress and power.

Additionally, 15w40 is ideally designed to operate in hotter temperatures than most gasoline motor oils.

What Is 15w40 Oil Used For? 

15w40 heavy-duty diesel engine oil is a premium fleet engine oil ideally designed to provide additional protection for over-the-road diesel trucks, farm tractors, off-highway diesel equipment, and buses that use Liquefied Natural Gas (LNG) or Compressed Natural Gas (CNG).

15w40 diesel engine oil is also used in passenger cars and light trucks fitted with diesel, gasoline engines, or turbocharged diesel engines.

How Do I Know 15w40 Is Bad For My Engine? 

Several telltale signs show that 15w40 diesel is bad for your engine and changing. They include:

The Check Engine Light Comes On

The most apparent sign that 15w40 diesel oil is bad for your engine will likely come from the car itself. The check engine light on your dashboard will illuminate if there is a problem with your 15w40 engine oil.

When the check engine light comes on, it indicates that things are so bad with the 15w40 oil that the engine is at risk of damage. This is usually due to the lack of adequate lubrication in the engine.

When the light comes on, it is best to go to your mechanic for inspection and repairs.

The Engine Is Knocking and Making Noise 

Good engine oil is supposed to provide a protective layer between engine parts. This helps avoid the brushing between metal parts and keeps your engine as quiet as possible. If the engine oil isn’t performing its function correctly, you will hear a lot of noise coming from the engine.

In some cases, the lack of lubrication will cause a knocking or rumbling noise. This indicates that your engine is wearing and tearing at a high rate, and you should change the 15w40 oil immediately before the damage intensifies.

The Oil Is Dark and Dirty 

Clean 15w40 engine oil has a slightly translucent color. The oil is supposed to keep your engine clean at all times. However, as the oil continues to be used, it will start accumulating soot and sludgy particles from the engine and turning darker by the day.

This is never an obvious sign, so you have to ensure that you check your engine oil at least once a month.

The Oil Smells Inside The Vehicle 

If you start smelling oil inside your car, it is a clear indication that 15w40 is no longer suitable for your engine, and it needs to be changed as soon as possible. If you smell exhaust fumes, it means your vehicle is overheating due to the lack of good and clean engine oil.

Exhaust Smoke 

Vehicles produce translucent exhaust smoke. However, if your vehicle produces dense exhaust smoke, it’s a sign that the 15w40 engine oil is no longer suitable for your engine, and it needs to be changed. If you don’t act fast enough, some engine parts may sustain damage with time.

Increased Fuel Consumption 

Bad engine oil can easily impact your vehicle’s performance and efficiency. If you notice that your vehicle has started consuming more fuel than usual, it’s a sign that the 15w40 oil has gone bad.

Can I Use 15w40 For Motorcycles? 

Yes. 15w40 should work fine in your motorcycle, provided that it is designed for a wet clutch system. Therefore, do not proceed to use a vehicle 15w40 engine oil on your motorcycle. You need to purchase 15w40 for motorcycles.

Why Is 15w40 Oil Preferred For Diesel Engines?

Generally, 15w40 engine oil doesn’t change so much with a temperature change. The engine oil is designed specifically for diesel engines, renowned for collecting carbon faster than gasoline engines. This is attributed to the fact that most diesel engines nowadays come with direct-injection designs.

Can I Put 15w40 Oil in a 10w30 Engine? 

Yes. However, if your vehicle’s engine is designed to use 10w30, it will deliver better performance and fuel economy if you use 10w30 engine oil over 15w40. This explains why most heavy-duty oils opt for 10w30 over the traditional 15w40.

Does 15w40 Have More Detergents? 

Yes. Diesel engine oils, including 15w40, have more detergents per volume than gasoline motor oils. Due to a blow-by in the engine, these detergents usually find their way inside the crankcase, which forces the engine oil to handle them.

If you put diesel oil with extra additives inside a gasoline engine, it will negatively affect your vehicle’s performance.

How Often Should I Change Diesel Oil? 

Experts recommend that people change diesel oil after every 5,000-7,000 miles. This is also the average recommendation for diesel oils on pickups that perform moderate towing.

However, if you don’t use your pickup to tow that often, you may be able to go longer without changing the diesel oil. On the other hand, if you tow frequently, it’s recommended that you change the diesel oil sooner than six months or 5000 miles.

Which Engine Oil Is Ideal For Diesel Engines?

Most diesel engines are usually rated between 15w40 and 5w40. The figure before ‘W’ indicates the engine oil’s thickness when it’s cold. On the other hand, the number that comes after indicates the engine oil’s thickness under average temperatures.

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