2022 Peterbilt 389 Fluid Specs

Quick Reference

Fluid	Type/Spec	Capacity
Engine Oil	API CK-4; SAE 15W-40 or 10W-30	10-12 gallons (PACCAR MX), ~15 gallons (Cummins X15)
Engine Coolant	Extended Life Coolant (ELC) - OAT	14-16 gallons
Transmission Fluid	Eaton PS-386 (Automated), SAE 50 (Manual)	7.5-16 pints (varies)
Rear Axle Fluid	SAE 75W-90 Synthetic Gear Lubricant	30-46 pints (total)
Power Steering Fluid	ATF Dexron III / Mercon	~3 quarts
Brake Fluid	DOT 3 / DOT 4 Hydraulic Fluid	N/A (Air Brakes)
Washer Fluid	API-certified Washer Fluid	~1 gallon
Diesel Exhaust Fluid (DEF)	API Certified (ISO 22241)	20-30 gallons

Engine Oil

For the 2022 Peterbilt 389, selecting the correct engine oil is critical for the longevity and performance of its heavy-duty diesel engine, whether it's equipped with a PACCAR MX or a Cummins X15. The required specification is API Service Category CK-4. This standard was introduced to provide enhanced protection against oil oxidation, viscosity loss due to shear, and oil aeration compared to previous categories, and is designed for the latest generation of low-emission diesel engines.

• Viscosity Grade: The most commonly recommended viscosity grade is SAE 15W-40, which offers robust performance across a wide range of operating temperatures. In colder climates, SAE 10W-30 may be used to improve cold-start performance. Always consult your owner's manual or engine manufacturer's guide for the precise viscosity recommendation based on your typical ambient temperature range.
• Capacity: Engine oil capacity varies significantly based on the engine installed. PACCAR MX-13 engines typically hold around 10-12 gallons (40-48 quarts), while the Cummins X15 can require up to 15 gallons (60 quarts). Always verify the exact capacity during an oil change by using the dipstick.
• Intervals: Oil change intervals are best determined by the truck's onboard monitoring system or the engine manufacturer's guidelines, which can range from 25,000 to 75,000 miles depending on duty cycle, fuel efficiency, and idle time.

Engine Coolant

The cooling system in a 2022 Peterbilt 389 requires a specific type of Extended Life Coolant (ELC). These are typically Nitrite-Free Organic Acid Technology (OAT) formulations. Using the wrong coolant can lead to corrosion, inhibitor dropout, and premature failure of water pumps, seals, and radiators.

• Specification: Look for a coolant that meets TMC RP-329 or ASTM D6210 standards. For PACCAR MX engines, a coolant meeting the PACCAR CS0185 specification is recommended. These are typically red or pink in color.
• Common Pitfall: Never mix ELC (OAT) coolants with conventional Inorganic Acid Technology (IAT) or Hybrid Organic Acid Technology (HOAT) coolants. Mixing can cause the chemical inhibitors to react negatively, forming a gel-like substance that clogs the cooling system. If the coolant type is unknown, a complete flush and fill is the safest course of action.
• Capacity: The cooling system capacity is substantial, typically ranging from 14 to 16 gallons.

Transmission Fluid

The correct fluid for the transmission depends entirely on whether the truck is equipped with an automated manual or a traditional manual transmission.

• Automated Manual (e.g., Eaton Endurant): These advanced transmissions require a specialized, synthetic lubricant. The primary specification is Eaton PS-386. Using a standard gear oil or ATF will damage the transmission.
• Manual Transmissions (e.g., Eaton Fuller): Traditional manual transmissions in these trucks use a high-viscosity fluid, typically a SAE 50 transmission fluid meeting Eaton PS-164 Rev 7.
• Capacity: Fluid capacity varies widely by transmission model, from as little as 7.5 pints to over 16 pints. Always check the fill plug level.

Rear Axle / Differential Fluid

Protecting the rear axles requires a high-quality, synthetic gear lubricant to handle the extreme pressures and temperatures generated under heavy loads.

• Specification: The standard specification is a SAE 75W-90 Synthetic Gear Lubricant meeting Dana SHAES 256 Rev C or Meritor O-76N.
• Capacity: Total capacity for both rear axles typically falls between 30 and 46 pints. Each axle housing has its own fill and drain plug.

Power Steering Fluid

The hydraulic power steering system requires a fluid that remains stable across a range of temperatures to provide consistent steering assist.

• Type: Most Peterbilt models specify a fluid meeting ATF Dexron III / Mercon specifications. This is a common automatic transmission fluid that also serves as a hydraulic fluid in this application.
• Note: Do not use dedicated "power steering fluid" unless it explicitly states it meets these specifications, as many generic fluids lack the required additives.

Brake System

The 2022 Peterbilt 389 is equipped with a full air brake system. It does not use hydraulic brake fluid for its primary service brakes. The system operates on compressed air stored in tanks, which is supplied by an engine-driven air compressor. Maintenance involves regularly draining the air tanks to remove moisture and monitoring the air dryer cartridge.

The only hydraulic fluid you may encounter is in the clutch system for manual transmissions, which typically uses DOT 3 or DOT 4 brake fluid in its reservoir.

Washer Fluid

Any high-quality, API-certified windshield washer fluid is acceptable. For winter use, select a fluid with an appropriate freezing point to prevent the reservoir and lines from freezing and cracking.

Diesel Exhaust Fluid (DEF)

As part of the Selective Catalytic Reduction (SCR) system, DEF is critical for emissions compliance. Using incorrect or contaminated fluid will trigger engine derates and costly repairs.

• Specification: DEF must be API Certified and meet the ISO 22241 standard. The container will carry the API certification mark.
• Common Pitfall: DEF is highly susceptible to contamination from dirt, fuel, or even tap water. Never use old or unmarked containers to store or transfer DEF. The DEF tank is exclusively for this fluid and is identified by a blue cap.
• Capacity: DEF tank sizes typically range from 20 to 30 gallons.

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