Peterbilt Model 389 · fluids
Fluids & Fill AmountsHow much oil, coolant, DEF and gear oil this truck takes, and what specification to buy.
Set the year first
Then read the How much column as a refill quantity, not a dry fill. Fill to the dipstick or sight glass and treat the number as a starting point — a drain never gets everything out.
Fill amounts for Peterbilt Model 389
| Fluid | How much | What to buy | Years | Source |
|---|---|---|---|---|
| Engine oil - Cummins X15, stamped steel pan (oil change)Change it: 25,000-60,000 mi by duty cycle | 43.5 qt (41.1 L) | API CK-4, Cummins CES 20086, 15W-40 | 2017–2023 | Verified |
| Engine oil - Cummins X15, aluminum pan (oil change)Change it: As above | 45.4 qt (43.0 L) wedge / 41.6 qt (39.4 L) rear center sump | As above | 2017–2023 | Verified |
| Engine oil - Cummins X15 (EPA 2024, pan and filter)Change it: 25,000-75,000 mi by mpg band | 9.6 gal (36.3 L) low to 11.6 gal (43.8 L) max | API CK-4, CES 20086 | 2024–2025 | Verified |
| Engine coolant - engine only (X15)Change it: Flush per OEM | 7.0 gal (26.5 L / 28 qt) | Fully formulated coolant meeting CES 14603 | 2024–2025 | Verified |
| Engine oil - PACCAR MX-13 (if fitted)Change it: 30,000-75,000 mi by duty | 42 U.S. qt (40.0 L) | API CK-4 / FA-4 | 2017–2025 | Verified |
| Diesel exhaust fluid (DEF) tankChange it: Fill at every fuel stop | Order-specific | ISO 22241 DEF | 2010–2025 | Unconfirmed |
| Fuel tankChange it: - | Order-specific | ULSD, 15 ppm max | 2007–2025 | Unconfirmed |
Sources: Cummins Quick Reference Guide 5410641 (X15 EPA 2017); Cummins Quick Reference Guide 6553662 (X15 EPA 2024); PACCAR MX-13 Operators Manual Y53-1100-1F1
Two ways to wreck an engine in five minutes
Overfilling an oil pan aerates the oil and can damage bearings. Running a cooling system low can crack a liner or a head before the gauge even moves. Fill slowly, then check the dipstick or sight glass twice.