Mazda Cosmo/121 (EU)

Additional Notes

• Both the 1800 and 2000 engine variants of the Mazda Cosmo/121 CD share an identical rear differential fluid capacity of 1.2 liters, indicating no displacement-related difference in the differential housing size between these two configurations.
• The 1.2-liter figure represents a service fill capacity, which is the volume required when refilling or topping up the differential under normal maintenance conditions rather than a full overhaul drain-and-fill scenario.
• Under normal use conditions, the rear differential fluid interval for both the 1800 and 2000 CD variants follows a dual-trigger schedule, with a check required at 10,000 km or every 6 months and a full fluid change at 20,000 km or every 12 months, whichever comes first.
• The dual-trigger interval structure, combining a distance threshold with a time-based threshold, reflects the understanding that fluid degradation occurs through both mechanical use and chemical aging over time, regardless of mileage accumulated.
• An initial service change interval of 1,000 km is specified for both the 1800 and 2000 CD variants, a notably short interval compared to the standard 20,000 km change cycle under normal use conditions.
• The 1,000 km initial service interval is associated with the break-in period of the differential, during which metal particles from newly machined gear and bearing surfaces accumulate in the fluid, making early fluid replacement a standard practice for fresh or rebuilt differentials.
• The capacity figure of 1.2 liters remains consistent across both the initial service and normal use rows for each variant, confirming the housing volume does not change between service contexts.