2025 Chevrolet Silverado 3500HD — Fluid Type Specifications

Quick reference

Fluid	Type/Spec	Capacity
Engine oil — 6.6L Gas (L8T)	SAE 0W-20, GM dexos1 Gen3, API SP	~8.0 qt (7.6 L) with filter — verify in owner’s manual/OEM info
Engine oil — 6.6L Duramax Diesel (L5P)	API CK-4; typical viscosities 10W-30 or 15W-40 (5W-40 synthetic for severe cold)	~10.0 qt (9.5 L) with filter — verify in owner’s manual/OEM info
Engine coolant (both engines)	GM Dex-Cool OAT (orange), premixed 50/50 deionized water	~14–22 qt (13–21 L) depending on engine/cooling package — verify
Automatic transmission (10-speed, Allison-branded)	GM DEXRON ULV ATF	Service refill ~7–8 qt (6.6–7.6 L); dry fill ~13–15 qt (12–14 L) — verify by RPO
Transfer case (4x4)	RPO NQH Autotrac: GM Auto‑Trak II (GM P/N 19369326); RPO NP2 manual: DEXRON‑VI ATF	~1.5–2.5 qt (1.4–2.4 L) depending on case — verify RPO
Front differential (4x4)	API GL-5 75W-90 full synthetic gear oil	~1.5–2.0 qt (1.4–1.9 L) — verify axle/RPO
Rear differential (SRW/DRW)	API GL-5 75W-90 full synthetic; some severe-duty packages may allow 75W-140. G80 locker typically does NOT require friction modifier.	~3.5–5.5 qt (3.3–5.2 L) depending on axle and SRW/DRW — verify RPO/axle size
Brake fluid	DOT 3 (FMVSS No. 116); GM P/N 19299570 or equivalent	Fill to MAX line; ~1–2 qt (0.95–1.9 L) for full system flush
Power steering	GM Power Steering Fluid (GM 9985010; ACDelco P/N 19329450/88901975 or equivalent) — do not use ATF	As needed; ~1–2 qt (0.95–1.9 L) for complete exchange
Washer fluid	Conventional methanol-based washer solvent suitable for climate	Typically 1.5–2.0 gal (5.7–7.6 L); fill to neck
Diesel Exhaust Fluid (Diesel only)	DEF meeting ISO 22241	~7–10 gal (26–38 L) depending on tank/wheelbase — verify

Engine oil

• 6.6L Gas (L8T): Use SAE 0W-20 oil that is officially licensed to GM dexos1 Gen3 and meets API SP. Do not substitute non-dexos oils.
• 6.6L Duramax (L5P): Use heavy‑duty diesel engine oil that meets API CK-4. GM commonly approves 10W-30 or 15W-40 depending on ambient temps and duty cycle; 5W‑40 synthetic is often recommended for severe cold or heavy towing in cold climates. Always match viscosity to your climate and follow the door‑label/owner’s manual.
• Intervals: Follow the Oil Life Monitoring (OLM) system. Severe service (heavy towing, idling, dusty environments) shortens intervals. Always replace the oil filter at each oil change.
• Pitfalls: Do not mix gasoline dexos1 oils in the Duramax; ensure jugs carry the appropriate licensing marks. For the gas V8, using non‑dexos oil can cause timing/lifter issues and warranty concerns.

Engine coolant

• Type: GM Dex‑Cool Organic Acid Technology (OAT), orange. Use ACDelco premixed 50/50 with deionized water or concentrate mixed to 50/50.
• Interval: Typically 5 years/150,000 miles initial; thereafter at shorter intervals per the service schedule. Verify for your RPO/config.
• Pitfalls: Never mix OAT Dex‑Cool with green HOAT/IAT coolants. Cross‑mixing shortens life and can form sludge. Duramax models do not use supplemental coolant additives (SCA); do not add nitrite/molybdate SCAs.

Automatic transmission fluid (10‑speed, Allison‑branded)

• Type: GM DEXRON ULV ATF only. Do not use DEXRON‑VI, “universal” ATF, or Allison TES‑295 fluids in this unit unless explicitly allowed by GM service information for your RPO.
• Capacity: Service refill after pan drain/filter typically ~7–8 qt; dry fill ~13–15 qt. Exact capacity varies by transmission variant, cooler, and line routing—verify in OEM service data.
• Interval: Follow the maintenance schedule. Severe service (frequent towing, high ambient temps, commercial duty) may call for shorter intervals. Use OEM procedures for thermal management and fluid level checks (temperature‑based).

Transfer case (4x4)

• Fluids by RPO:
  • NQH (Autotrac, 2‑speed with Auto 4WD): GM Auto‑Trak II fluid (blue), GM P/N 19369326 (superseded from 88900402).
  • NP2 (manual/part‑time 2‑speed): DEXRON‑VI ATF.
• Capacity: ~1.5–2.5 qt depending on case. Always confirm by RPO and model year service info.
• Interval: Severe‑service towing/off‑road often 45,000–60,000 miles; otherwise per maintenance schedule.
• Pitfalls: Do not substitute generic ATF in Autotrac cases; use Auto‑Trak II only. Using the wrong fluid can cause clutch chatter and failure.

Front and rear differentials

• Type: API GL‑5 full‑synthetic gear oil; 75W‑90 is commonly specified. Some severe‑service packages or hot‑climate/towing uses may allow 75W‑140—follow the axle/RPO guidance.
• Capacities: Front IFS ~1.5–2.0 qt. Rear AAM 11.5"/12.0" typically ~3.5–5.5 qt (SRW vs DRW and axle size). Verify by RPO and axle tag.
• Limited slip note: The G80 automatic locking differential generally does NOT require friction modifier. Do not add LSD additive unless the axle label/service info specifically calls for it.
• Interval: Severe towing/hot use can require changes at ~45,000 miles; otherwise per maintenance schedule. After initial heavy towing break‑in, some axles call for an early fluid change—check the manual.

Brake fluid

• Type: DOT 3 (FMVSS No. 116). GM P/N 19299570 or equivalent.
• Interval: Replace periodically (commonly every 2–3 years) or as specified by GM. Moisture contamination raises boiling point risk for heavy towing.
• Pitfalls: Do not mix silicone DOT 5. Keep reservoir clean; wipe cap area before opening.

Power steering

• Type: GM Power Steering Fluid that meets GM 9985010 (ACDelco P/N 19329450/88901975 or equivalent). Do not use ATF.
• Service: Inspect level regularly. Exchange fluid if contaminated, after steering component replacement, or as needed.
• Pitfalls: Using ATF can swell seals and cause pump noise/failure.

Washer fluid

• Type: Conventional methanol‑based washer solvent appropriate for your climate (de‑icer in winter).
• Service: Fill to the neck. Avoid mixing brands that gel in extreme cold.

Diesel Exhaust Fluid (Duramax only)

• Type: DEF meeting ISO 22241 (32.5% urea/67.5% deionized water).
• Capacity: ~7–10 gal depending on tank and wheelbase—verify in the owner’s manual.
• Notes: Store between 23–77°F (‑5 to 25°C). Do not add water or fuel. Use clean DEF‑rated funnels/pumps only. Top off before long trips/tows; an empty DEF tank will trigger reduced‑power mode.

If your 2025 Silverado 3500HD has unique RPO codes, snow‑plow/camper packages, dual rear wheels, or upfit cooling, capacities and some fluid allowances can differ. When in doubt, verify in the owner’s manual or OEM service information for your exact VIN.

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