Is 15W40 Oil As Good As 30W In Diesel Tractor Engines?-15W40 vs. 30W Oil

Is 15W40 Oil As Good As 30W In Diesel Tractor Engines?

Is 15W40 Oil As Good As 30W In Diesel Tractor Engines?-15W40 vs. 30W Oil

Is 15W40 Oil As Good As 30W In Diesel Tractor Engines?(Short Answer)

If the engine of your diesel tractor is only used in areas where temperatures do not drop below freezing, then 30W oil could be a good choice. If, however, your tractor operates under fluctuating temperatures, 15W40 oil is suggested. 

The benefit of 15W40 oil is its ability to be more efficient during cold start-ups and provide better protection for engines. The only disadvantage using 15W40 oil is in extreme cold temperatures. 

In most situations 15W40 oil can be as effective as 30W oil on diesel tractor engines, providing flexibility and lubrication that is effective across temperatures of all kinds.

Also read: Kubota 10W30 Oil, Synthetic or Dino?

 Choosing The Right Oil for Your Diesel Tractor:

Key Factors:

  1. Climate:

Freezing Temperatures:

  • Below the temperature of -18°C: Strongly consider 15w40. The lower viscosity (15w) allows for faster cold starts as well as better fluid flow even in cold conditions.
Tractor engine oil Below the temperature of -18°C
Source: Bard

2.-18°C to 0°C:

  • 30w is possible when used just occasionally at these temperatures.
  • 15W40 is still a better security.
  • Warm Climates (rarely below 0°C):
  • 30w may be adequate. But, it can provide benefits such as:
  • Decreased degradation of oil when temperatures are high.
  • potential improvements to fuel efficiency for certain engines.

3.Your Tractor’s Manual:

Prioritize the recommended viscosity of oil. It considers your engine’s specifications and operating conditions. If you don’t pay attention, it may harm the engine.

4. Engine Age and Wear:

  • Older engines (designed to use straight-weight oil)
  • Talk to a professional prior to applying 15w40. Looser tolerances might cause leaks in oil.
  • Engines that are newer: Designed for multi-grade oils such as 15w40.

Also read: What Kind of Engine Oil Did Old Tractor Use?

General Tips:

  • If the temperature drops frequently to below -18°C , Choose 15w40.
  • If temperatures aren’t often below 0°C , and your manual advises 30W: 30w is likely to be sufficient.
  • To get a wider range of temperature or better performance, think about 15w40, even in hot climates.
  • Always refer to your user instructions and talk to your mechanic in case you’re not sure.
viscosity grade of tractor engine oil
Source: Green Tractor Talk

Also read: Why Is There Oil On Engine Near Firewall Tractor?

Compatibility With Older Engines:

Engine Age and Design:

  • Pre-1970s Engines: These primarily used straight-weight oil like 30w. The switch to 15w40 could cause leaks in the oil ( potential leak increase 5-15%) due to the looser tolerances. Get the advice of a mechanic prior to making the switch.
  • 1970s-1990s Engines: Often designed for multiple-grade oils, such as 15w40. The switch from 30w to 15w40 is usually secure.
  • Post-2000 engines: Designed for modern multi-grade oils that meet API standards. Follow manufacturer’s recommendations.

Also read: Can I Burn Tractor Hydraulic Oil In My Diesel Engine?

2. Mileage and Wear:

  • Low Mileage (less than 50k miles): 15w40 might work, but you must take into consideration the recommendations of the manufacturer first.
  • Moderate Mileage (50,000-100,000 miles): 15w40 or an oil designed to be high-mileage specifically for older vehicles could be suitable. Ask a mechanic to help you make the right option.
  • High Mileage (more than 100,000 miles): Stick to the manufacturer’s recommendations or choose oil that is specifically made to be used on older vehicles that could have leaks.
Tractor Engines oil of High Mileage (more than 100,000 miles) of tractor
Source: Machinery Lubrication

3. Climate:

  • Warmer Climates: 15w40 could be too much while 30w might be enough.
  • Moderate Climates 15w40 is a better option for protection throughout the year.
  • Cold climates: 15w40 is generally suggested for colder starts as well as lubrication.

Also read: Can Diesel Engine Oil Be Used in a Gas Engine Tractor?

SAE 30 vs. 15W40

1. Operating Temperature:

  • SAE 30: Viscosity range at operating temperature: 100°C (212°F): 9.3 cSt (minimum), 12.5 cSt (maximum). Suitable for temperatures above -18°C (0°F).
  • 15W40: Viscosity range at operating temperature: 100°C (212°F): 15.6 cSt (minimum), 21.9 cSt (maximum). Suitable for wider temperature ranges, including colder environments.

2. Cold Cranking Viscosity:

  • SAE 30: Cold cranking viscosity at -18°C (0°F): 3,500cP (maximum).
  • 15W40: Cold cranking viscosity at -15°C (5°F): 3,500cP (maximum). 15W indicates better cold-start performance.

3. Shear Stability:

  • SAE 30: May thin out more at high operating temperatures compared to 15W40.
  • 15W40: Contains additives to resist thinning at high temperatures, providing better viscosity stability.

4. Engine Age and Wear:

  • Older engines: Designed for straighter-weight oils like SAE 30. Switching to 15W40 might lead to increased oil leaks due to looser tolerances. Consult your manual or mechanic.
  • Newer engines: Designed for multi-grade oils like 15W40, benefiting from its wider viscosity range and better protection.

What Is The Difference Between 15W 40 and 10W-30 diesel?

15W-40 as well as 10W-30 are multi-grade oils that are commonly found in diesel engines. Here are some major differences between them:

What Is The Difference Between 15W 40 and 10W-30 diesel?
Source: Car fuel advisor

1. Viscosity:

  • 15W-40:
    • Winter (W) rating: 15. The rating indicates the oil’s ability to pump when temperatures are cold. The lower numbers will flow more efficiently during colder temperatures, allowing more rapid cold start.
    • High-temperature viscosity: 40. The oil’s thickness is measured when it’s heated. The higher numbers provide greater resistance to wear and tear in high temperatures of operation.
  • 10W-30:
    • Winter (W) rating: 10. Better cold-flow performance when in comparison to 15W-40.
    • High-temperature viscosity: 30. A lower viscosity than 40. This means less friction, and possibly increased fuel efficiency.

2. Key Differences in Numbers:

  • Cold flow 10W-30 is slightly more efficient when operating at lower temperatures as compared to 15W-40 (5degC in comparison to. 12°C as the pump point).
  • High-temperature protection 15W-40 is a more thick oil film when heated to extreme temperatures (40 instead of. 30 viscosity ratings) and could offer more wear-resistant.

Choosing The Right Oil:

The choice of the best oil is based upon a number of variables:

  • Climate:
    • Colder conditions: 10W-30 might be adequate if temperatures don’t dip below -12°C .
    • Variable climates 15W-40 provides greater protection against temperature, able to handle cool summers and cold winters.
  • Wear and tear on the engine:
    • Engines older than HTML0: They could benefit from more oil, like 15W-40, because of the possibility of looser tolerances.
    • Modern engines designed for use with multigrade oil, such as 10W-30 and 15W-40, based on the manufacturer’s specifications.
  • Synthetic: Conventional Synthetics provide superior performance, but they are also more costly.
  • API Standards Check that the fuel is in compliance with the API standards for the diesel engine you are using.

What Oil Should I Use In My Diesel Tractor?

The process of selecting the correct engine oil may be a bit difficult particularly with the numerous brands and grades available. Let’s take it all down to help you to choose the right lubricant to suit your needs:

For Heavy Duty Diesel Engines:

  • John Deere Plus50 II (SAE 15W-40): This all-rounder offers excellent protection to both the older and more modern diesel engines. It offers prolonged time between drains (up at 500 hours! ) When paired to John Deere filters and fights corrosion, wear and the buildup of sludge. Consider it the reliable option to choose.
  • John Deere Plus50 II (SAE 10W-30): Offers similar features as the 15W-40 however shines more in cooler temperatures. If temperatures are freezing it will allow for faster starting of the engine.
  • John Deere PLUS 50 II (SAE 1W-40 Synthetic): The ultimate performance oil, this synthetic is the best at extreme temperatures ranging from -40°F up to 122°. It provides excellent control over sludge and soot which makes it suitable in harsh conditions.
  • John Deere 10W-30 break-in: This factory-filled oil was made specifically to be used on newly built or rebuilt engines. Use it during the initial 100 hours to guarantee the proper breaking-in.

Regarding Heavy Duty Gas and Light Duty Diesel Engines:

  • John Deere TorqGard (SAE 5W-30): This high-performance oil performs well in beginning at low temperatures for diesel and gasoline engines. Select this oil if you work under cold conditions.
  • John Deere’s Torq-Gard (SAE 30): This straight-weight oil shines best in extreme temperatures, high-performance applications especially for old gasoline engines. It is a superior choice for wear deposits, oxidation, and protection.

For Gas Engines:

  • John Deere TurfGard (SAE 10W-30): This versatile oil can be used with a range of tools for gardening and lawn such as mowers, tillers and generators. It offers reliable protection to your yard’s daily activities outdoors.

What Weight of Diesel Motor Oil: SAE 10W30 or 15W40?

If you are you are comparing SAE 10W30 and the 15W40 diesel motor oil the decision is based on a variety of aspects, such as viscosity and the design of the engine. This is a brief overview:

Ease of Pumping and Shearing:

  • SAE 10W30: Lower viscosity makes it easier to pump and less prone to shearing, which can contribute to improved fuel economy and power, particularly in engines designed for this viscosity grade.
  • SAE 15W40: While still suitable for heavy-duty applications, the higher viscosity of SAE 15W40 oil may result in slightly more resistance to pumping and shearing compared to SAE 10W30.
  • Engine Age:
    • Newer Engines (post-2000): Designed for multi-grade oils like 10W30 and benefit from their wider viscosity range and potential fuel economy improvements.
    • Older Engines (pre-2000): Designed for straighter-weight oils like 15W40. Using 10W30 might lead to leaks due to looser tolerances. Consult a mechanic before switching.

Operating Climate:

  • Temperature Range:
    • Warm Climate (above 25°C): Both oils might be suitable, but consult your manual. Consider 10W30 for potential fuel economy benefits.
    • Temperate Climate (0°C to 25°C): 10W30 offers better cold starts and wider protection.
    • Cold Climate (below 0°C): 5W30 or lower might be necessary for easier cold starts.


  • Lower viscosity (e.g., 10W30) flows easier at low temperatures, potentially aiding cold starts and improving fuel economy by 1-2% in some cases.
  • Higher viscosity (e.g., 15W40) provides thicker oil film at high temperatures, offering better wear protection, especially in older engines.

15w40 vs. 10w30 Engine Oil: The Key Differences


  • 15w40: Higher viscosity, thicker at operating temperatures, offering better wear protection, especially in older engines or hot climates (up to 40°C).
  • 10w30: Lower viscosity, thinner at operating temperatures, allowing easier cold starts and potentially improving fuel economy (up to 2%).

Operating Temperature:

  • 15w40: Suitable for a wider range of temperatures (-18°C to 40°C), ideal for extreme climates or engines that run hot.
  • 10w30: Primarily recommended for warmer climates (above 0°C), might struggle with cold starts in freezing conditions.

Engine Age:

  • 15w40: Often preferred for older engines (pre-2000) designed for straighter-weight oils due to potential leaks with thinner oils in worn tolerances.
  • 10w30: Generally suitable for newer engines (post-2000) designed for multi-grade oils and their wider viscosity range.

Additional Factors:

  • API Service Category: Ensure the chosen oil meets the API service category specified in your manual (e.g., CJ-4 for modern diesels).
  • Synthetic vs. Conventional: Synthetic oils offer superior performance and protection but are typically more expensive.

Is Using 15W40 Oil Suitable For an Old Tractor?

Yes, using 15W40 oil in an old tractor can be suitable, especially if it meets or exceeds the warranty requirements of most manufacturers of diesel and gasoline engines. This oil is specifically formulated for older engines and higher sulfur fuels, making it a reliable choice for maintaining the performance and longevity of your tractor.

Additionally, many users have reported using 15W40 oil in various equipment, including tractors and pickups, without encountering any issues over extended periods, demonstrating its effectiveness and reliability.


While 15w40 oil offers wider temperature protection and higher viscosity for wear control, it isn’t necessarily “as good” as 30w for ALL diesel tractor engines. The best choice depends on your specific tractor’s manual recommendation, engine age and wear, operating climate, and API service category. Always prioritize the manufacturer’s advice and consult a mechanic for expert guidance based on your unique situation. Remember, using the wrong oil can harm your engine, so personalized advice is crucial for optimal performance and longevity.

Video Guide:

Frequently Asked Questions:

What are the advantages of using 15W40 oil over 30W in diesel tractor engines?

15W40 oil typically provides better cold start performance and flows more easily at low temperatures, offering improved engine protection during startup. It may also offer enhanced fuel efficiency and power output in certain conditions.

In what situations would 30W oil be preferable over 15W40 for diesel tractor engines?

30W oil may be preferred in applications where engines are subjected to consistently high temperatures, heavy loads, or prolonged operation. It offers robust protection against wear and heat-induced breakdown under extreme conditions.

Can I mix 15W40 and 30W oil in my diesel tractor engine?

While it’s generally not recommended to mix different viscosity grades of oil, in an emergency situation, it’s better to top up with the same viscosity grade currently in use. However, for routine maintenance, it’s best to stick to one viscosity grade recommended by the manufacturer.

How do I know which viscosity grade is best for my diesel tractor engine?

Refer to your tractor’s manual or consult with a qualified mechanic to determine the recommended viscosity grade for your specific engine model. Factors such as climate, operating conditions, and manufacturer recommendations should be considered when selecting the appropriate oil viscosity.

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