This is a common question for John Deere lawn mower owners looking to use a different viscosity oil than recommended by the manufacturer. While 5W-30 oil may seem similar to 10W-30, there are some important differences to consider before using it in your John Deere mower.
Page Contents
The Short Answer
John Deere specifies 10W-30 oil for most of their lawn mowers and using a lighter viscosity oil like 5W-30 instead can potentially lead to increased wear or engine damage over time. 5W-30 flows faster when cold which can lead to premature wear during cold starts. 10W-30 is the recommended viscosity grade for most ambient temperatures and provides a balance of cold flow and high temperature protection.
How Oil Viscosity Ratings Work
Motor oil viscosity refers to its thickness and ability to flow at certain temperatures. The viscosity grade of oil is identified by two numbers such as 10W-30. The first number followed by the “W” refers to the oil’s cold temperature or winter flow rating. A lower number means the oil will flow easier when cold. The second number refers to the oil viscosity at high operating temperatures. A higher second number means the oil is thicker when hot.
10W-30 oil provides the following viscosity properties:
- Flows like an SAE 10 grade oil when cold.
- Thickens to the viscosity of an SAE 30 oil when hot.
- Provides balanced performance in most ambient temperatures.
5W-30 oil flows faster when cold but may thin out too much when hot. It provides:
- Easier flow when cold starting like a SAE 5 grade oil.
- Thickens to the viscosity of an SAE 30 oil when hot.
- Good cold start performance but may lack high temperature film thickness.
Why John Deere Specifies 10W-30
John Deere engineers have determined 10W-30 is the optimal viscosity grade recommendation for most of their lawn mower engines. Here are some of the reasons why:
- 10W-30 works well across a wide range of ambient temperatures providing balanced performance in cold weather and hot conditions.
- When cold starting, 10W-30 flows just well enough to properly lubricate and minimize wear during initial start-up.
- The 10W-30 grade thickens to SAE 30 at operating temperature, providing sufficient oil film thickness and high temperature protection.
- John Deere lawn mowers generally use splash lubrication. A 10W-30 weight oil adheres better to engine parts than lighter 5W-30 oil.
Thinner oils like 5W-30 can flow too quickly when cold allowing insufficient time for the oil to properly coat and lubricate critical engine components during cold starts. This can lead to increased wear over time.
Once fully warmed up, a 5W-30 may thin out more than ideal at high engine temperatures. This can reduce the oil’s film thickness and ability to keep engine parts properly separated and lubricated under load and at higher rpm speeds.
Potential Issues Using 5W-30 Instead of 10W-30
Using 5W-30 oil instead of the manufacturer recommended 10W-30 viscosity grade does provide some potential downsides:
- Increased wear – Thinner 5W-30 will flow faster when cold which reduces lubrication protection during cold starts. This can increase engine wear over time.
- High temperature protection – 5W-30 may thin out more at higher temperatures reducing lubrication and cooling of internal engine components.
- Reduced film thickness – The lighter 5W-30 grade won’t cling as well or provide as robust of an oil film which can increase friction and wear.
- Oil consumption – Lower viscosity oils have higher volatility meaning they burn off and evaporate easier in high heat contributing to potential oil consumption issues.
- Voiding warranty – Using non-recommended viscosity grades can technically void factory powertrain warranties if engine damage results.
Evaluating Your Specific Mower and Usage
While 10W-30 is the recommended oil for most John Deere mowers, some factors that may potentially allow using 5W-30 oil include:
- Operating in very cold climates where starting viscosity is a priority.
- An older engine with higher mileage and increased internal clearances.
- Mower usage is infrequent or under lighter loads and lower temperatures.
- 5W-30 synthetic blends which provide superior film thickness than conventional 5W-30 oils.
Owners should refer to their owner’s manual for the specific oil viscosity recommendation for their mower. If considering using 5W-30, evaluate the mower’s usage and conditions it operates under to determine if the lighter viscosity grade makes sense or could cause problems.
Oil Change Intervals
When running 5W-30 instead of 10W-30, it’s wise to reduce oil change intervals. The lighter viscosity oil will break down faster than a 10W-30 grade oil. Changing oil more frequently can help reduce the risks associated with using a 5W-30 viscosity.
Adding Oil Supplements
Certain oil supplements can enhance 5W-30 oil to improve its performance. Oil additives containing higher levels of zinc and phosphorus anti-wear additives can help compensate for the thinner oil. Additional high temperature dispersants can also improve the 5W-30’s thermal stability and ability to keep things lubricated at higher temperatures.
However, too much supplement additives can also have detrimental effects. Unless the oil supplement is specifically designed to improve a 5W-30 oil, restraint should be used to avoid creating more problems.
Switching Between Viscosity Grades
Avoid mixing different viscosity grades of oil together. It’s best to completely drain the existing motor oil before switching to a different viscosity. Mixing oils like 10W-30 and 5W-30 can negate the benefits of either viscosity grade.
Changing oil viscosity should also coincide with a fresh oil change. Introducing a new viscosity grade into old, degraded oil is not recommended.
Synthetic Oil Options
Full synthetic 5W-30 oils provide superior cold flow properties and high temperature film strength over conventional 5W-30 oils which are blended from Group II and Group III base oils. The improved performance characteristics of synthetics make them a better option if choosing to run a 5W-30 viscosity grade in a lawnmower specifying 10W-30.
Synthetic 5W-30 oils that carry resource conserving “Energy Conserving” and “Resource Conserving” designations indicate formulations engineered for fuel economy. These can provide additional protection against oil thinning at high temperatures. Look for 5W-30 synthetics that carry GM’s dexos1 GEN 2 specification for a higher quality option when considering a lighter viscosity grade.
Comparison of Different 5W-30 Oil Types
| Oil Type | Cold Flow | High Temp. Protection | Cost |
|---|---|---|---|
| Conventional 5W-30 | Good | Fair | Cheap |
| Synthetic Blend 5W-30 | Better | Good | Moderate |
| Full Synthetic 5W-30 | Excellent | Very Good | Premium |
Conclusion
While 5W-30 oil may seem like a perfectly suitable substitute for 10W-30 in a John Deere lawn mower, there are some definite trade-offs in terms of reduced cold flow protection and high temperature performance. Sticking with the manufacturer’s recommended 10W-30 viscosity grade is the safest approach for most mowing conditions and applications.
5W-30 may offer easier cold weather starting for mowers used primarily in very cold climates only. Operators should carefully consider potential increased wear, especially during short trip cold starts, before using 5W-30 in place of 10W-30 per John Deere’s specifications. If choosing to run a 5W-30 due to specific conditions, a high quality full synthetic 5W-30 along with shortened oil change intervals can help minimize the risks.