5w40 vs 15w40 oil: What Should You Choose?

Engine oil ensures smooth running, longer engine lifespan, and reduced fuel consumption in both gasoline and diesel engines. Plenty of engine oil options out there in the market left you no choice but to confuse. Your motor engine needs oil just like you need water to live. Choosing the right oil for the engine of your vehicle is the best bargain for longevity and reliability. Here we will discuss the two most favored lubricant products in the market: 5w40 vs 15w40.

Are you wondering which engine oil to choose that would best fit your vehicle? No worries at all, you’ll get a clear insight about these two engine oils by the end of this article. 

5w40 is a synthetic oil while 15w40 motor oil is available in both mineral/conventional and semi-synthetic forms.  Both have multi-grade characteristics protecting at the start-up as well as at the operating temperatures. 

The conventional oils are made multigrade by adding sufficient amounts of these two additives – pour point depressants (PPD), and viscosity index improvers (VII). The difference is that the base oil of synthetic engine oil already has multigrade properties and has no or very small amount of PPDs and VIIs in it. Both these oils contain a few more additives like anti-wear, dispersants, anti-foam, detergents, rust inhibitors, and corrosion inhibitors.

Why is the weight of oil important?

The Society of Automotive Engineers (SAE) has designed a coding system based on the viscosities of the engine oils. They used ‘w’ to name these multi-grade engine oils which refers to ‘winter’ (not weight). In the case of 5w40 oil, the figure that appears before ‘w’ refers to the viscosity or weight of oil at low temperatures (tested at -30oC or -22oF) and the number after ‘w’ refers to the viscosity or weight of oil at high temperature (tested at 40oC or 104oF). Thus, we can say that an SAE 40 weight oil acts like a 5-weight oil in the winter. 

5w40 has a wider range of temperature applications. This engine oil can be used in the temperature range of -30oC and +40oC (-22oF to 104oF). The 15w40 motor oil has a temperature range of -20oC to +40oC (-4oF to 104oF). 

Both these engine oils are multi-weight oils having the ability to adjust their weights at varying temperature degrees. They maintain a specific range of viscosities i.e., a relatively low viscosity (not too thick) to flow at a cold start and a relatively high viscosity (not too thin) to protect the engine at the high operating temperatures. So, we can say that 5w40 works better in colder climate conditions and 15w40 does a better job in a warmer environment.

Pros of 5w40

  • More flowability so can get to the moving parts of the engine rapidly.
  • Has a sufficient number of detergents to avoid deposit build-up.
  • Improve engine performance by providing quick acceleration.
  • Protect the engine from wear and tear for long.
  • Enhance engine power to provide a good cold start.
  • Save fuel economy.
  • Synthetic oils can retain their viscosity grade much better than a conventional motor oil at the end of the oil change interval.
  • Less frequent oil change intervals i.e., up to 9000 miles or 15000 kilometers.
  • Fairly wide operating temperature range of use.
  • Has good heat resistance at extreme operating temperatures.
  • Can be used all year but is preferred in winters.
  • Produce lower hydrocarbon emissions than conventional oils.

Cons of 5w40

  • Synthetic oils having high production costs are more expensive than 15w40.
  • Used preferably in new car engines within the warranty period.
  • Cannot be used in more worn-out engines.
  • Can expose leaks due to high cleaning strength.
  • Some manufacturers don’t recommend using 5w40.
  • Has occasional supply shortages in the market.

Pros of 15w40

  • Protect the engine within the first few minutes at the starting point.
  • Better at reducing engine wear at high operating temperatures.
  • Promotes the cleaning of sludge.
  • Prevents the corrosion of parts.
  • Provides better protection in engines having more than 60,000 miles.
  • Improves oil pressure in older engines.
  • Save fuel economy in the worn-out engines in the market.
  • Can be used all year round but is preferred in summers.
  • Production cost is less than synthetic oils so less expensive than 5w40.

Cons of 15w40 

  • Conventional oil needs to change more often typically not exceeding 3000 miles or 5000 kilometers.
  • Additives have started to break down near the end of oil change intervals.
  • Unable to maintain its viscosity grade properties in extreme operating temperatures.
  • Cannot be used in cold areas as oil loses its characteristics below -20oC.
  • Have high HC and CO2 emissions.
  • Some manufacturers don’t agree to use 15w40 in their engines.

5w40 vs 15w40 – Difference in Viscosity

Viscosity is the fluid’s resistance to flow; thus, it has an indirect relationship to the flowability of engine oils meaning that the low viscosity oils have high flowability (thin oil) and high viscosity oils have less flowability (sticky and thick oil). The viscosity also depends upon the temperature i.e., if the temperature rises, the oil viscosity will drop.

5w40 vs 15w40 viscosity

Good engine oil has the ability to maintain a specific viscosity range at cold and hot temperatures. 5w40 and 15w40 have different viscosity grades at cold temperatures (-30oC and -20oC) but have the same viscosity grades at higher operating temperatures (40oC). 5w40 oil has a winter viscosity grade of 5 which means it is less viscous than 15-grade oil (15w40) at very low temperatures.

5w40 vs 15w40 – Difference in Price

The price of motor oils depends upon the production cost. Since the production cost of synthetic 5w40 oil is more than the 15w40 motor oil, it is expensive. The economic status also depends on the availability and consumption levels. 5w40 oil users experience an occasional shortage of this oil in the market. 15w40 motor oil being available all the time and also widely used in various engines is way cheaper than 5w40.   

5w40 (1 quart)

$14.34 – Quicksilver 4-Stroke ATV engine oil

$14.94 – Pennzoil Platinum Euro motor oil

$15.30 – Schaeffer manufacturing co. SynShield OTR Plus diesel engine oil

$19.29 – Red Line motor oil

$19.41 – Motul Gen2 motor oil

$20.55 – Liqui Moly Top Tec 4100 motor oil

$21.99 – Mobil 1 Advanced Formula M motor oil

$23.97 – Motul NISMO competition engine motor oil

$24.47 – Castrol Edge A3-B4 Advanced motor oil

$25.00 – Shell Rotella T6 Diesel engine oil

15w40 (1 quart)

$8.75 – Brad Penn Penn-Grade 1 semi-synthetic motor oil

$9.49 – Green Forest Heavy-duty Diesel engine oil

$9.95 – MPT Ten-K diesel motor oil

$11.30 – STAR BRITE Pro Star Heavy-duty motor oil

$12.75 – Kohler diesel engine motor oil

$15.78 – Ultra1Plus Synthetic motor oil

$16.50 – Cummins Onan motor oil

$16.86 – Shell Rotella T4 Triple protection conventional motor oil

$17.10 – Mobil 1 Diesel engine oil

$18.99 – Pennzoil/Quaker state motor oil

5w40 vs 15w40 – Difference in Fuel Economy

Fuel economy is a measure of the rate of fuel consumption by motor engines. A low-viscosity oil flows faster through the engine due to reduced resistance and drag in the moving parts of the engine. 

Less energy is required by the pump to push the oil for sufficient lubrication providing exceptional wear protection. Such motor oils increase the fuel economy and help to run like a new vehicle.

5w40 oil is thinner as compared to 15w40 oil at very low temperatures. So, it saves more fuel economy in colder climatic conditions. 

5w40 vs 15w40 – Difference in Applications 

15w40 motor oil has a larger application range than 5w40. It is widely used in the engines of various models of trucks and is easily accessible all the time due to its cheap price. 

Most of the trucks running out on the roads have a worn-out engine and 15w40 provides better protection to such older vehicles.

What you should choose?

First of all, you need to check your car manual for recommended engine oil options. Try to use those engine oils mentioned by your vehicle manufacturer. Another very important point to consider is the condition of your vehicle’s engine. The condition depends upon the mileage years and driving dynamics of the driver. Now, consult any experienced mechanic in the tuning shop who will help you to choose the correct oil for your vehicle.

Some points to consider before purchasing oil are as follows:

  • Consider the purpose of use (motor oil or gear oil)
  • Rely on its viscosity (5w40 or 15w40 etc.)
  • Check if the oil meets API and ACEA specifications
  • See whether it has the OEM approvals and their respective codes

The decisive factor in this situation is the climatic conditions of your area. Because if you live in colder areas where the temperature is low, you should go for 5w40. Otherwise, 15w40 can be used in normal climatic conditions effectively. 

Can I use 15w40 instead of 5w40?

Most of the new vehicles use 5w40 oil but one can shift to 15w40 as the engine gets older. It improves oil pressure in the older engine thus saving fuel economy.

If you have a normal ambient atmosphere, you can shift from 5w40 to 15w40 as it can maintain sufficient viscosity grade and provide better protection to the engine at the start-up. 

Another advantage of shifting from 5w40 to 15w40 is the low cost. 15w40 oil, being a cheaper motor oil, proves to be a cost-effective choice.

Final words on 5w40 vs 15w40

5w40 and 15w40 motor oils can be used with complete success in a variety of gasoline and diesel engines for heavy-duty diesel trucks, farm tractors, gasoline passenger cars, off-highway diesel vehicles, light-duty gasoline trucks, turbo-charged diesel engines, etc. 

The choice will depend on the weather condition of your area. 5w40 motor oil will flow more easily to start your engine in low-temperature areas. It has a wide range of use in terms of temperature but is preferred in the winter season. 15w40 motor oil is best suited for worn-out engines. Besides being cheaper, it improves oil pressure and saves fuel economy in older vehicles.