Can I Top Up Semi-Synthetic Oil with Fully Synthetic Oil?

Yes, you can top up semi-synthetic oil with fully synthetic oil. Both types of oil are compatible, as they are derived from similar base oils. However, mixing the two may alter the properties of the oil, such as viscosity and performance characteristics.

Consider These Points Before Mixing Oils

(Viscosity): Ensure that the viscosity rating, such as 5W-30, of the synthetic oil you are adding matches that of the semi-synthetic oil currently in your engine.

(Brand Compatibility): It is generally advisable to use oils from the same brand or at least from reputable manufacturers to ensure compatibility even if the oil types are different.

(Performance): While topping up with synthetic oil is acceptable, keep in mind that the overall performance may not match that of using fully synthetic oil exclusively. Semi-synthetic oils may contain different additives which can affect the performance.

Long-Term Considerations

If you plan to switch to fully synthetic oil, consider doing a complete oil change instead of just topping up. This can help maintain optimal engine performance. Fully synthetic oil typically offers superior performance in extreme temperatures, better engine protection, and longer oil life. Mixing it with a synthetic blend will slightly reduce these benefits.

Bottom Line

Topping up semi-synthetic oil with fully synthetic oil is fine but, for the best results, it is better to use the same type of oil consistently. Any oil is better than no oil, but regular synthetic oil offers superior performance benefits.

Specific Example

Yes, you can mix 5W-30 semi-synthetic synthetic blend oil with 5W-30 fully synthetic oil. Both types of oil have the same viscosity rating (5W-30) and are made from base oils that are generally compatible with each other. However, the performance you’ll get will be slightly worse than the one you’ll get when using fully synthetic oil only. Full synthetic oil typically offers superior performance in extreme temperatures, better engine protection, and longer oil life. Mixing it with a synthetic blend will slightly reduce these benefits.

Additional Considerations

(Performance): Understand that when mixing synthetic oils, you won't get the full performance benefits of using fully synthetic oil exclusively. Semi-synthetic oils may contain different additives that can affect the performance.

(Practical Advice): Mixing synthetic oils may also degrade the quality of the fully synthetic oil faster. This is because the imperfect nature of hydrocarbon chains in semi-synthetic oils can cause pure synthetics to break down more quickly than they normally would. Therefore, the reverse is much worse. Do not add semi-synthetic oil to synthetic oil as it will increase the degradation rate of the full synthetic.

(Regular Maintenance): Always go back to your regular oil change interval and don't think that you could go as far as regular synthetic oil would.