Can I use 5W40 instead of 5W-30?
Yes, in many cars you can substitute 5W-40 for 5W-30, but only if your manufacturer approves it and the oil meets the same specifications. 5W-40 provides stronger protection at higher operating temperatures and heavy loads, but it can affect cold-start performance and fuel economy if the OEM does not authorize the change.
Understanding what the numbers mean
Both 5W-30 and 5W-40 are multi-grade oils. The first number (5W) describes cold-start viscosity, with the “W” indicating winter performance; they behave similarly at startup. The second number indicates viscosity at engine operating temperature (100°C). The higher the number, the thicker the oil remains when hot. Moving from 30 to 40 high-temperature viscosity generally increases film strength and protection in hot conditions, but can reduce flow at startup and slightly impact fuel economy.
Why this matters for your engine
The exact impact depends on your engine design. Some engines tolerate a wider oil range, especially turbocharged or high-performance units, while others require the tighter clearances and cooling characteristics of a specific viscosity. Using an oil grade not approved by the manufacturer can affect lubrication, emissions, and warranty coverage.
When 5W-40 may be acceptable or advantageous
Consider these scenarios, but only if your manual or dealer confirms compatibility. Before making any switch, verify the oil specification and approvals match or exceed what the OEM requires.
- Engine is designed for high-temperature operation or routinely experiences sustained high loads (towing, hot climates, long highway runs).
- Engine is turbocharged or has higher heat output where thicker oil can improve film strength.
- Owner’s manual lists 5W-40 as an acceptable alternative (explicitly or as an “or” grade).
- Oil approvals (such as API/ACEA certifications and OEM designations like MB 229.x, VW 502.x, BMW Longlife, etc.) meet or exceed the engine’s requirements.
In these cases, switching can be reasonable. However, if the manual specifies only 5W-30, or if no OEM approval for 5W-40 is given, sticking with the recommended grade is the safer choice.
Practical guidance by vehicle type
General guidance by typical engine scenarios can help, but always confirm with your manual or dealer before changing oil grades.
- Modern turbocharged or performance engines: Often tolerate or even require a higher high-temperature viscosity. Check the exact OEM spec.
- Naturally aspirated, non-turbo engines with tight tolerances: Usually prefer the manufacturer’s specified grade; a different grade may affect lubrication balance.
- Hot climate or heavy-duty use (tow, excursions): 5W-40 may offer beneficial protection if approved by the manufacturer.
- Cold climates or when fuel economy is a priority: 5W-30 typically provides better cold-start flow and can improve efficiency when approved by the manufacturer.
Bottom line: the best choice is the grade approved by the vehicle’s manufacturer for your specific engine and conditions.
How to switch safely if you get the green light
If you confirm that 5W-40 is an acceptable alternative, follow these steps to minimize risk and maximize performance.
- Verify the oil specification: ensure the 5W-40 meets the same API/ACEA specs and OEM approvals as the 5W-30 you’re replacing.
- Match the viscosity to the engine’s design: ensure the 40-grade is within the acceptable high-temperature range for your engine model.
- Choose a quality oil: use synthetic or synthetic-blend oils that carry the correct approvals for your vehicle.
- Change the oil and filter: perform a full oil change with a new filter to avoid contaminants and ensure proper flow.
- Monitor after the switch: check for unusual oil pressure readings, leaks, or oil consumption, and schedule a follow-up inspection if anything seems off.
Following these steps helps ensure that switching to 5W-40, when approved, delivers the intended protection without unintended side effects.
What to do if you’re unsure
If you’re uncertain about whether 5W-40 is suitable for your car, take these precautions:
- Consult the owner’s manual or the dealership for approved viscosity ranges and OEM approvals.
- Ask a trusted mechanic to review your engine’s design, age, and expected operating conditions.
- Use the same brand and grade consistency for oil changes to avoid mixing incompatible oils.
Sticking with the manufacturer’s recommended grade remains the simplest path to reliable lubrication and warranty protection.
Summary
5W-40 can be a valid substitute for 5W-30 in some engines and climates, provided the manufacturer explicitly approves the change and the oil carries the same OEM certifications. The key factors are engine design, operating conditions, and official specifications. If in doubt, follow the manufacturer’s guidance, and consider consulting a dealer or qualified mechanic before altering the recommended oil grade.
