Quick answer
Adding an oil additive to a half-full sump is possible, but you must account for correct dosage. If the sump isn’t at normal capacity, you risk overdiluting or overconcentrating the additive’s effect.
Detailed answer
The standard instructions often assume a full oil capacity—for example, one bottle per 4–5 quarts. If your sump is only half full due to partial draining or ongoing consumption, you must scale the additive accordingly. Overly concentrated solutions can raise viscosity, cause foaming, or unbalance the existing additive package. Too diluted means minimal impact. Ideally, it’s best to add the product at an oil change with full capacity. But if you’re topping up, do some math: half capacity may need half the recommended dose. Keep records of how much oil is in there and adjust accordingly.
