Can I put 5w40 on top of 5W30?
Yes, you can top up with 5W-40 if your vehicle’s specification allows it and both oils meet the same manufacturer-approved standards. This is generally acceptable as a short-term measure, but it should not be treated as a long-term replacement for the recommended grade.
How viscosity and mixing work
Engine oil viscosity describes how the oil behaves at different temperatures. The first number, followed by the “W,” indicates cold-start flow, while the second number indicates viscosity at operating temperature. Mixing 5W-30 and 5W-40 will produce a blend whose high-temperature viscosity falls somewhere between the two. The exact result depends on the proportion of each oil and their formulations. Manufacturers specify a acceptable viscosity range for each engine, and using oil outside that range can affect protection, efficiency, and warranty coverage.
Important caveats when mixing oils
- Always verify that both oils meet the same API/ACEA specifications and any OEM approvals. Mixing different basestocks or incompatible specs can reduce performance or protection.
- Check your owner’s manual or the oil cap label for the recommended viscosity range. Some engines are designed strictly for 5W-30 or another specific grade, and deviating long-term can affect warranty and wear characteristics.
- Consider climate and driving conditions. In hot climates or under heavy-load conditions, a thicker oil like 5W-40 can offer better protection, but in cold climates, 5W-30 may be preferable for easier starts and quicker lubrication on startup.
Guidelines for topping up or changing oil
Before proceeding with a top-up or a switch, consider the following guidelines to help you decide when and how to proceed.
- Verify the vehicle’s official viscosity range and approvals in the owner’s manual or on the oil filler cap.
- Ensure both oils meet the same API/ACEA specification and any OEM approvals required for your engine.
- Use 5W-40 only as a temporary top-up if your manual allows it; plan a future oil change with the recommended grade if possible.
- Avoid blending oils from different manufacturers with incompatible additives or basestocks unless explicitly approved by the OEM.
- Monitor for any changes in oil level, color, or odor after the top-up; if you notice unusual signs, consult a technician.
In short, follow the manufacturer’s guidance and treat a 5W-40 top-up as a short-term adjustment rather than a permanent replacement for 5W-30 or the recommended grade.
Practical steps to take
If you’re considering a top-up now or planning an upcoming oil change, use these steps to proceed safely.
- Consult the owner’s manual to confirm the approved viscosity range and any OEM restrictions.
- Choose an oil that matches the approved spec and, if possible, use a 5W-40 only if explicitly permitted for your engine.
- When topping up, add a small amount first (about 0.5 liter or 1 pint) and recheck the oil level with the dipstick after running the engine briefly.
- Run the engine for a few minutes, check for leaks, and recheck the level to ensure you’re within the correct range.
- If oil appears discolored or smells burnt, or if you’ve overfilled, address the issue promptly and consider an actual oil change with the recommended grade.
- Plan a full oil change using the recommended viscosity as soon as feasible to restore optimal protection.
These steps help minimize risk and ensure you stay within the engine’s designed operating parameters while you arrange a proper oil change.
Bottom line
For most vehicles, topping up with 5W-40 when you already have 5W-30 in the engine is acceptable only if the manufacturer allows it and the oils share the same essential specifications. It’s usually best treated as a temporary measure, with a plan to return to the manufacturer-recommended viscosity at the next oil change. Always prioritize the OEM specifications and seek professional advice if you’re unsure.
Summary
Oil viscosity matters because it affects cold-start protection, lubrication efficiency, and high-temperature film strength. Mixing 5W-30 and 5W-40 is commonly possible if the oils are within the approved specification range, but it should not replace a proper oil change with the correct grade. Check the owner’s manual, ensure compatible specifications, consider climate and driving conditions, and aim to revert to the recommended viscosity at the next service. When in doubt, consult a qualified technician.
