In general, it is acceptable to top up a semi-synthetic oil with fully synthetic oil. Both types of oils are compatible with each other and typically have similar chemical compositions. However, there are a few considerations to keep in mind:
Compatibility: Most modern engine oils, whether semi-synthetic or fully synthetic, are designed to be compatible with each other. Mixing a small amount of fully synthetic oil with semi-synthetic oil during a top-up is unlikely to cause any issues.
Consistency: It's advisable to maintain consistency in the type of oil used for your engine. If you regularly use semi-synthetic oil, it's generally better to continue using it rather than frequently switching between different oil types. Consistency helps ensure that the oil properties, additives, and performance characteristics remain consistent throughout the oil change intervals.
Oil Specifications: Pay attention to the oil specifications recommended by your vehicle manufacturer. Ensure that the fully synthetic oil you're using for the top-up meets the requirements and viscosity grade specified in your vehicle's owner manual. This ensures the oil provides adequate lubrication and protection for your engine.
Mixing Ratio: When topping up with fully synthetic oil, try to keep the mixing ratio as low as possible. It is generally recommended to keep the ratio of fully synthetic oil to semi-synthetic oil below 50%. However, if you have any concerns or specific questions, it's always a good idea to consult the vehicle's manufacturer or a qualified mechanic.
Remember, regular oil changes at the recommended intervals using the correct type and grade of oil are essential for maintaining your engine's health and performance. If you have any doubts or concerns about oil compatibility or your vehicle's specific requirements, it's best to consult a professional mechanic or refer to the manufacturer's recommendations for the most accurate advice.