Equivalence charts are useful and also over-trusted. They match viscosity and additive family; they do not know what is already in your sump.
Match the duty, not the label
Viscosity grade, TBN and the maker's approval list are the three things to check. A grade that matches on viscosity alone can be wrong for a high-sulphur fuel or for a cylinder oil feed rate set for something else.
Mixing is the real risk
Different additive chemistries in the same sump can drop out. Where a top-up is unavoidable, keep it small, log it, and plan a change at the next opportunity.
When to wait
For hydraulic and turbine systems with tight cleanliness specifications, waiting a day for the correct product costs less than a filter campaign later.
What to send us
- Send the current oil in use and its TBN
- State the fuel sulphur content
- Ask for the maker's approval letter
