Brief answer: The 2008 Honda Civic Si with a 6-speed manual transmission uses Honda Manual Transmission Fluid (MTF). Use Honda MTF or an approved equivalent that explicitly meets Honda’s MTF specification. Do not use automatic transmission fluid (ATF) or engine oil in the manual gearbox.
In more detail, the Civic Si from 2008 relies on a dedicated manual transmission fluid designed for Honda’s gearbox components and friction characteristics. While Honda’s own MTF remains the safest choice, there are aftermarket fluids that claim compatibility when specifically labeled as meeting Honda’s MTF specification. Always verify the product label and consult the owner's manual or a Honda service bulletin to ensure you’re using the correct formulation for your region and transmission model.
Official specification and acceptable options
What Honda recommends
The factory specification for the Civic Si’s 6-speed manual transmission calls for Honda Manual Transmission Fluid (MTF). Honda MTF is designed to protect gears and synchronizers under typical street and performance driving, and it avoids the additives found in ATF that aren’t suitable for manual gearboxes.
Before listing options, note that your best option is to source Honda MTF from a dealership or reputable parts supplier. If you cannot obtain Honda MTF, you may use aftermarket fluids that explicitly state compatibility with Honda MTF specifications, but you should avoid fluids labeled only as ATF or engine oil for this application.
Options in practice include:
- Honda Manual Transmission Fluid (MTF) — the official fluid for the 6-speed manual Civic Si transmission.
- Aftermarket fluids that explicitly meet Honda’s MTF specification (often labeled as “MTF” or “MTF-S” on the bottle). Verify the product documentation confirms compatibility with Honda manual transmissions.
- Avoid using automatic transmission fluid (ATF) or engine oil in the manual gearbox, as they are not designed for this use and can cause shifting and wear issues.
Conclusion: Use Honda MTF if available. If you must use an aftermarket option, ensure it is explicitly listed as meeting Honda’s MTF specification and avoid ATF/engine oil in the manual transmission.
How to change the transmission fluid in a 2008 Civic Si
If you’re performing a drain-and-fill service, follow a careful process to ensure proper lubrication and level. The steps below outline a typical procedure for a manual transmission fluid change on this model.
- Warm the vehicle and safely raise the front end on jack stands to access the transmission drainage and fill plugs.
- Place a drain pan beneath the transmission, then remove the drain plug to let old fluid drain completely.
- With the drain plug out, remove the fill plug (or access port) to ensure you can refill after draining.
- Reinstall the drain plug after the fluid has fully drained, then refill with the recommended Honda MTF (or an approved equivalent) until the level reaches the fill plug hole.
- Reinstall the fill plug, clean up any spilled fluid, and lower the vehicle.
- Test drive to verify smooth shifting and recheck the fluid level if necessary after the engine has cooled.
Capacity and level tips: The manual typically holds roughly two quarts of fluid for a full drain-and-fill, but exact capacity can vary by transmission variation and year. Start with the recommended amount and top off until the fluid begins to seep out of the fill hole or reaches the indicated level on the fill plug, as described in the service manual.
Practical considerations and cautions
Always confirm the exact specification for your region and vehicle by consulting the owner’s manual or a Honda dealership. If you notice hard shifting, grinding, or delayed engagement after a fluid change, recheck that you used the correct MTF and that the transmission is at the proper operating temperature and level.
Summary
For a 2008 Honda Civic Si with a 6-speed manual transmission, the recommended fluid is Honda Manual Transmission Fluid (MTF). Use Honda MTF whenever possible; if not available, choose an aftermarket fluid that explicitly states compatibility with Honda MTF specifications, and avoid ATF or engine oil in the manual gearbox. Follow proper drain-and-fill procedures and verify the fluid level after the refill. When in doubt, consult the owner’s manual or a Honda service professional for region-specific guidance.