Quick answer
To add an oil additive, ensure compatibility with your oil, follow the label’s dosage, and pour it into the crankcase via the oil filler cap. For flush-style additives, run the engine briefly, then drain immediately.
Detailed answer
Different additives have different instructions. Some stay in for the entire oil interval; others need a quick drain. Read the product label carefully—especially regarding whether the engine should be warm or cool. Use a funnel if the additive is thick to prevent mess. Once added, run the engine to circulate it, then monitor any changes in noise or leaks. If you’re using a short-term additive (like a flush), remember to change the oil once its prescribed time is up.
