2021 Peterbilt 389: Complete Fluid Specifications
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Quick Reference
| Fluid | Type/Spec | Capacity (approximate) |
|---|---|---|
| Engine Oil | API CK-4 / FA-4 ( Cummins CES 20086 / 20092, PACCAR PS-222) | 40-48 quarts (depending on engine) |
| Engine Coolant | OAT (Organic Acid Technology) - Red/Purple Extended Life Coolant (e.g., TMC RP 329, Cummins CES 14603) | 60-80 quarts (varies by system configuration) |
| Transmission Fluid (Manual) | Eaton PS-164 Rev 7 / PS-386 | 13.5-16.5 quarts (varies by model) |
| Transmission Fluid (Automatic) | Allison TES 668 / TES 295 | 40-70 quarts (varies by model) |
| Front Differential | Meritor O-76N (SAE 80W-90 / 85W-140) | 16-20 quarts (varies by axle) |
| Rear Differential | Meritor O-76N (SAE 80W-90 / 85W-140) | 16-20 quarts (varies by axle) |
| Brake Fluid | DOT 4 (Air Brake Systems) | N/A (system dependent) |
| Power Steering Fluid | Eaton PS-164 Rev 7 or equivalent (e.g., Shell Spirax S4 CX, Mobil DTE 10 Excel 46) | 3-5 quarts |
| Washer Fluid | Commercial Grade Windshield Washer Solvent | 1-2 gallons |
| DEF (Diesel Exhaust Fluid) | ISO 22241 (API DEF Certified) | 15-30 gallons (varies by tank size) |
Engine Oil
For the 2021 Peterbilt 389, the engine oil specification is crucial for longevity and performance, especially given the heavy-duty nature of these trucks. Most Peterbilt 389s from this era are equipped with either Cummins or PACCAR engines. Both manufacturers typically recommend high-quality API CK-4 or FA-4 oils.
- API CK-4: This is a robust oil designed for diesel engines, offering excellent wear protection, oxidation stability, and shear stability. It is backward compatible with most older engines where CJ-4, CI-4 Plus, CI-4, and CH-4 oils are recommended.
- API FA-4: This is a newer category of oil designed for modern diesel engines to provide improved fuel economy. It is very important to note that FA-4 oils are not backward compatible with all older engines and should only be used if specifically recommended by the engine manufacturer. Using FA-4 in an engine not designed for it can lead to premature wear.
Manufacturer-Specific Specs:
- Cummins Engines: Look for Cummins CES 20086 (for CK-4) or CES 20092 (for FA-4). Always verify the correct specification in your engine
More specs for the 2021 Peterbilt 389
Oil Capacity & Filter
Capacity, weight, filter PN, drain plug torque, change interval.
Coolant Capacity & Type
Total system capacity, OEM coolant spec, flush interval, bleed tips.
Transmission Fluid & Service
Trans model, fluid spec, capacity, filter PN, service interval.
Torque Specifications
Lug nuts, drain plug, caliper, axle nut, plug, key fasteners.
Brake Pad & Rotor Specs
Pad PNs, rotor size, min thickness, caliper torque.
Tire Size & Pressure
OEM size, cold psi, bolt pattern, wheel size, TPMS.
Battery Size & Group
Group size, CCA, AGM/flooded, dimensions, reset note.
A/C Refrigerant & Oil
R-134a or R-1234yf, charge oz, PAG oil spec.
Bulb Sizes (Headlight, Tail, Fog)
Headlight, fog, tail, turn, reverse, interior.
Factory Maintenance Schedule
Service intervals by mileage, severe-duty notes, known issues.
Towing Capacity & Payload
Max tow, payload, GVWR/GCWR, hitch class by trim.
Fuse Box Diagram & Amperage
Fuse box locations, layout, amps, and what each fuse controls.
Serpentine Belt Routing & Length
Belt routing, length, rib count, OEM + aftermarket PNs.
Wheel Alignment Specifications
Camber, caster, toe ranges (front & rear), adjustability notes.
Paint Color Codes
All factory colors with paint codes, sticker location, touch-up tips.
Wiper Blade Sizes
Driver/passenger/rear blade size, attachment, OEM + cross-refs.
Spark Plug Type & Gap
Plug PN, gap, torque, interval by engine.
Transmission & Axle Gear Ratios
Trans gear ratios, axle ratios, RPO codes, tow vs MPG impact.
Key Fob Programming
DIY programming steps, FCC ID, fob PN, battery, transponder.
Same spec — other model years
Maintenance & repair guides
2021 Peterbilt 389 Maintenance Schedule →
Available maintenance guidance; confirm the manufacturer schedule.
Repair planning references →
Plan the scope of work; detailed procedures need configuration-matched evidence.
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Values can vary by engine, trim and build date; check your VIN-specific service information. Updated 2026-06-26.