The 2018 Honda Civic Si requires SAE 0W-20 full synthetic engine oil. This is the official specification for the turbocharged 1.5-liter engine, and it’s best to use a high-quality oil that meets Honda’s requirements.
Oil type and specifications
Climate considerations and service notes
Maintenance and service reminders
Summary
In short, your 2018 Civic Si should run on SAE 0W-20 full synthetic oil, preferably Honda Genuine Motor Oil 0W-20 or another high-quality synthetic that meets Honda’s specifications. Adhering to this specification helps protect the turbocharged engine and maintains performance over time.