2018 Kenworth W900 Fluid Type Specifications

Quick Reference

Fluid	Type/Spec	Capacity
Engine Oil	API CK-4 or FA-4 (depending on engine); Viscosity per engine manufacturer	Varies by engine model (e.g., PACCAR MX-13: ~42.0 quarts, Cummins X15: ~44.0-48.0 quarts)
Engine Coolant	PACCAR MX Extended Life Coolant (ELC) or equivalent (e.g., CAT EC-1, Cummins CES 14603); OAT, Red/Purple	Varies by cooling system configuration and engine model (typically 50-70+ quarts)
Transmission Fluid	Eaton PS-386 (for Eaton Fuller manual transmissions); Allison TES-295 or TES-389 (for Allison automatics)	Varies by transmission model (e.g., Eaton Fuller: 13.5-16.5 quarts; Allison: 29-74 quarts)
Front Differential	SAE 80W-90, API GL-5 (standard); SAE 75W-90 synthetic (for extended drain)	Varies by axle model (typically 12-25 pints)
Rear Differential	SAE 80W-90, API GL-5 (standard); SAE 75W-90 synthetic (for extended drain)	Varies by axle model (typically 15-30 pints per axle)
Power Steering Fluid	Eaton PS-164 Rev 7 or equivalent (e.g., Dexron VI, Mercon V)	Varies by system (typically 4-6 quarts)
Brake Fluid	DOT 4 Heavy Duty	Varies by system (generally 1-2 quarts)
DEF	ISO 22241 (API DEF certified)	20-25 gallons
Washer Fluid	Commercial Windshield Washer Fluid	1-1.5 gallons

Engine Oil

For a 2018 Kenworth W900, the engine oil specification is highly dependent on the specific engine installed. Kenworth W900s are commonly equipped with PACCAR MX-13 or Cummins X15 engines.

For PACCAR MX-13 engines: PACCAR recommends using oils that meet the API CK-4 or API FA-4 specification. The choice between CK-4 and FA-4 depends on the engine and its design, with FA-4 being a lower high-temperature high-shear (HTHS) viscosity oil designed for improved fuel economy in newer engines. Always verify the correct specification in your owner's manual. Viscosity grades typically recommended include SAE 10W-30 or 5W-30 for fuel economy, or 15W-40 for traditional applications, dependent on ambient temperatures.

For Cummins X15 engines: Cummins generally recommends API CK-4 specified oils. Similar to PACCAR, the preferred viscosity can vary based on operating temperatures, with 15W-40 being common, and 10W-30 or 5W-30 for colder climates or fuel economy purposes. Consult your specific engine's owner's manual for the precise Cummins Engine Oil Specification (CES) which might include codes like CES 20086 (for CK-4).

Capacity: Engine oil capacity varies significantly by engine model. For a PACCAR MX-13, expect approximately 42.0 quarts. For a Cummins X15, capacities can range from 44.0 to 48.0 quarts. Always confirm with the dipstick and manufacturer specifications during a change.

Intervals and Pitfalls: Engine oil change intervals are crucial for heavy-duty trucks and can range from 20,000 to 75,000 miles or more, depending on oil analysis, duty cycle, and the use of synthetic oils. Extended drain intervals require oil analysis to monitor oil condition and engine wear. Using the incorrect oil specification (e.g., an older API CI-4 in an engine designed for CK-4/FA-4) can lead to premature wear, reduced fuel economy, and potential warranty voidance. Never mix oils of different specifications.

Engine Coolant

Kenworth trucks equipped with PACCAR engines typically use an Extended Life Coolant (ELC), which is an Organic Acid Technology (OAT) formulation, often reddish-purple in color. This coolant is designed for long service intervals and excellent corrosion protection.

Specification: PACCAR MX Extended Life Coolant (ELC) or an equivalent meeting specifications such as CAT EC-1, Cummins CES 14603, or Detroit Diesel DFS93K217. These are generally nitrate-free, phosphate-free, and silicate-free OAT coolants.

Capacity: The cooling system capacity depends on the engine, radiator size, and auxiliary coolers, but it's substantial, typically ranging from 50 to over 70 quarts (12.5-17.5 gallons) for a W900.

Intervals and Pitfalls: ELC coolants offer extended service intervals, often up to 600,000 miles or 6 years, with proper monitoring and topping off. It's critical not to mix OAT coolants with conventional (inorganic additive technology – IAT) or hybrid OAT (HOAT) coolants, as this can lead to gel formation, reduced corrosion protection, and premature failure of cooling system components. Always drain, flush, and refill the entire system if switching coolant types. Use only distilled or deionized water for dilution if purchasing concentrate, or better yet, use pre-mixed 50/50 coolant.

Transmission Fluid

Transmission fluid specifications are entirely dependent on the transmission model installed in your W900.

Eaton Fuller Manual Transmissions: Eaton Fuller manual transmissions are very common in Kenworth W900s. Eaton specifies their proprietary Eaton PS-386 fluid for most of their modern manual transmissions. This is a synthetic or semi-synthetic heavy-duty gear lubricant designed for extended drain intervals. Some older or specific models might use an API GL-4 or GL-5 gear oil, but PS-386 is the predominant recommendation for most 2018 models.

Capacity: Eaton Fuller manual transmission capacities typically range from 13.5 to 16.5 quarts.

Allison Automatic Transmissions: If your W900 is equipped with an Allison automatic transmission, the fluid requirements will differ. Allison generally specifies Allison TES-295 for extended drain intervals, or Allison TES-389 for standard duty/drain intervals. TES-295 is a fully synthetic fluid offering superior performance and thermal stability.

Capacity: Allison automatic transmission capacities can vary widely depending on the model, from approximately 29 quarts to up to 74 quarts for some larger models with external coolers. Always consult the Allison owner's manual for exact figures.

Intervals and Pitfalls: Follow the manufacturer's recommended service intervals. For Eaton PS-386, extended drain intervals often exceed 500,000 miles depending on application and fluid analysis. Allison TES-295 also offers extended drains, often beyond 150,000 miles. Never use "universal" ATF in an Allison transmission; always use a TES-295 or TES-389 approved fluid. For Eaton transmissions, ensure the fluid meets the PS-386 specification to ensure component longevity and proper shift feel.

Differential Fluid (Front and Rear)

Kenworth W900s utilize heavy-duty drive axles requiring robust gear oils.

Specification: For both front (if applicable, typically a steer axle) and rear differentials, a heavy-duty SAE 80W-90, API GL-5 gear oil is the standard recommendation. For extended drain intervals, improved fuel economy, or severe service, a SAE 75W-90 synthetic, API GL-5 fluid is often specified. Certain heavy-duty applications or axles may recommend SAE 85W-140, consult your specific axle manufacturer's specifications (e.g., Meritor, Dana).

Capacity: Differential capacities vary by axle model. Front steer axle hubs typically hold a small amount of grease. Rear differentials can hold anywhere from 15 to 30 pints per axle. Tandem axle configurations will require fluid for both differentials.

Intervals and Pitfalls: Differential fluid intervals can range from 100,000 to 250,000 miles for conventional oils, with synthetic options often extending well beyond that. Always check for manufacturer-specific drain intervals. Ensure the fluid meets the API GL-5 rating, as GL-4 is not sufficient for hypoid gears found in differentials and will not provide adequate protection. If an axle is equipped with a limited-slip differential (LSD), a friction modifier additive may be required, though this is less common in heavy-duty truck drive axles and more prevalent in light-duty applications. Confirm with the axle manufacturer.

Power Steering Fluid

Specification: For Kenworth W900s, the power steering system often specifies Eaton PS-164 Rev 7 or an equivalent fluid. Other acceptable fluids may include automatic transmission fluids that meet Dexron VI or Mercon V specifications, which are highly stable synthetic or semi-synthetic fluids. Always consult the steering gear manufacturer's recommendations.

Capacity: Power steering system capacities vary, but typically range from 4 to 6 quarts.

Intervals and Pitfalls: Power steering fluid is often overlooked. While not as critical as engine oil or transmission fluid, it should be periodically inspected and changed. Intervals can be around 100,000 miles or when the fluid appears discolored or develops a burnt smell. Using an incorrect fluid can lead to premature wear of the power steering pump and steering gear, leading to expensive repairs. Never use conventional power steering fluid designed for light-duty vehicles unless explicitly stated by the manufacturer.

Brake Fluid

Heavy-duty trucks like the Kenworth W900 use air brakes primarily. However, the hydraulic brake system for the clutch (if manual) or certain auxiliary systems will use a hydraulic fluid.

Specification: For hydraulic clutch systems or any other hydraulic braking components, DOT 4 Heavy Duty brake fluid is the standard recommendation due to its higher wet boiling point compared to DOT 3, which is important for heavy-duty applications.

Capacity: The capacity for any hydraulic brake or clutch system is generally small, typically 1 to 2 quarts.

Intervals and Pitfalls: Brake fluid (DOT 3, 4, 5.1) is hygroscopic, meaning it absorbs moisture over time, which lowers its boiling point and can lead to corrosion. It should be flushed and replaced every 2-3 years, or according to manufacturer recommendations, to maintain braking performance and prevent seal degradation. Do NOT use DOT 5 silicone-based fluid in a system designed for DOT 3, 4, or 5.1, as they are not compatible and can cause severe system damage.

Diesel Exhaust Fluid (DEF)

For any diesel engine equipped with Selective Catalytic Reduction (SCR) to meet emissions standards, DEF is essential.

Specification: DEF must meet ISO 22241 (API DEF certified) specifications. This ensures the correct urea concentration (32.5%) and purity. Using non-compliant DEF can damage the SCR system and lead to costly repairs.

Capacity: The DEF tank on a 2018 Kenworth W900 typically holds between 20-25 gallons.

Intervals and Pitfalls: DEF is consumed continually while the engine is running. The fill interval depends on fuel consumption and engine load. Always ensure you have sufficient DEF. Store DEF in a cool, dry place out of direct sunlight. DEF has a shelf life, typically 1-2 years, so avoid purchasing in large quantities unless you have high consumption. Do NOT put DEF in the diesel fuel tank or vice-versa, as this will cause severe engine damage. The nozzle sizes are different to help prevent this.

Washer Fluid

Specification: Any good quality commercial windshield washer fluid is suitable. Many commercial fluids offer enhanced cleaning properties and freeze protection.

Capacity: Windshield washer fluid reservoir capacity is typically 1 to 1.5 gallons.

Intervals and Pitfalls: Top off as needed. In freezing climates, ensure the fluid has adequate freeze protection to prevent the reservoir and lines from freezing and rupturing.

Find a trusted shop on Repairius.