2020 GMC Sierra 1500 Complete Fluid Specifications Guide

As an ASE-certified master technician, I regularly see modern trucks rolling into the bay with complex fluid requirements. Gone are the days when you could pour 10W-30 into the engine and a universal Dexron into the transmission and call it a day. The 2020 GMC Sierra 1500 (part of the T1XX generation) offers a wide array of powertrains, from the turbocharged 2.7L four-cylinder to the mighty 6.2L V8 and the highly efficient 3.0L Duramax diesel. Using the correct, factory-specified fluids is non-negotiable if you want to maintain your warranty and prevent catastrophic failure.

Here is the complete fluid specification guide for the 2020 GMC Sierra 1500.

Quick reference

Fluid	Type/Spec	Capacity
Engine Oil (4.3L V6)	5W-30 (GM dexos1™ Gen 2/Gen 3)	6.0 qt (5.7 L)
Engine Oil (2.7L I4)	5W-30 (GM dexos1™ Gen 2/Gen 3)	6.0 qt (5.7 L)
Engine Oil (5.3L V8)	0W-20 (GM dexos1™ Gen 2/Gen 3)	8.0 qt (7.6 L)
Engine Oil (6.2L V8)	0W-20 (GM dexos1™ Gen 2/Gen 3)	8.0 qt (7.6 L)
Engine Oil (3.0L Diesel)	0W-20 (GM dexosD™ / ACEA C5)	7.0 qt (6.6 L)
Engine Coolant	Dex-Cool® OAT (Orange/Pink)	11.2 – 14.5 qt (Varies by engine)
Transmission (6-Speed)	DEXRON®-VI ATF	Varies, verify in OEM service info
Transmission (8-Speed)	Mobil 1 Synthetic LV ATF HP (Blue Label)	Varies, verify in OEM service info
Transmission (10-Speed)	DEXRON® ULV	Varies, verify in OEM service info
Transfer Case (4WD)	DEXRON®-VI or Auto-Trak II (Verify RPO code)	1.6 qt (1.5 L)
Front Differential	75W-90 Synthetic Gear Oil	1.5 qt (1.4 L)
Rear Differential	75W-90 Synthetic Gear Oil	2.5 - 2.8 qt (Varies by axle size)
Brake Fluid	DOT 4 Hydraulic Brake Fluid	Fill to MAX line
Power Steering Fluid	N/A (Electric Power Steering)	N/A
Diesel Exhaust Fluid (DEF)	API Certified ISO 22241	~5.0 Gallons (Diesel only)
Windshield Washer	Standard Washer Fluid	Fill to top

Note: Capacities are approximate and include filter changes where applicable. Always verify in the owner's manual / OEM service info before filling.

Engine Oil

General Motors has strictly enforced its dexos specification for over a decade. For the gasoline engines (2.7L, 4.3L, 5.3L, and 6.2L), you must use an oil meeting the dexos1 Gen 2 or newer Gen 3 specification. The V8s require a thin 0W-20 weight for fuel economy and tight bearing clearances, while the 2.7L and 4.3L utilize 5W-30.

If you drive the 3.0L Duramax turbo-diesel, you must use dexosD 0W-20. Do not confuse this with standard dexos1 or older CJ-4/CK-4 heavy-duty diesel oils. DexosD is a light-duty diesel specification designed to protect the emissions equipment (like the DPF) while maximizing fuel economy. Interval: Follow the Oil Life Monitor (OLM), but never exceed 7,500 miles or 12 months.

Engine Coolant

Every 2020 GMC Sierra 1500 uses GM's Dex-Cool® coolant, which is an Organic Acid Technology (OAT) antifreeze. It is typically orange or a pinkish-orange color. Common Pitfall: Never mix Dex-Cool with older green Inorganic Additive Technology (IAT) coolants or universal "all-makes, all-models" fluids. Mixing OAT with other formulas can cause the coolant to gel, leading to plugged heater cores and blown head gaskets. Interval: Replace every 5 years or 150,000 miles, whichever comes first.

Transmission Fluid

The 2020 Sierra came with three different transmissions, and fluid specs are radically different:

1. 6-Speed (6L80): Uses standard DEXRON®-VI.
2. 8-Speed (8L90): This unit is notorious for torque converter shudder. GM issued a service bulletin mandating the use of Mobil 1 Synthetic LV ATF HP (distinguished by a blue label on the bottle) to cure and prevent the shudder. Do not use standard Dexron-VI.
3. 10-Speed (10L80): Co-developed with Ford, this transmission requires an ultra-low viscosity fluid: DEXRON® ULV. Interval: Severe service (towing, city driving) dictates a fluid and filter change at 45,000 miles.

Transfer Case (4WD Models)

For four-wheel-drive models, fluid requirements depend on the specific transfer case installed. Single-speed transfer cases typically use DEXRON®-VI, while the two-speed active transfer cases often require GM's Auto-Trak II fluid (which is distinctly blue). You must verify your specific RPO code (found in the glove box or door jamb) against OEM service info to avoid damaging the transfer case clutches. Interval: Check every 22,500 miles, change every 45,000 miles under severe duty.

Front and Rear Differential

Both the front and rear differentials on the 2020 Sierra require 75W-90 Synthetic Gear Oil. If your truck is equipped with the G80 automatic locking rear differential (the "Eaton Locker"), do not add limited-slip friction modifiers. The G80 locker relies on a specific friction threshold to engage the flyweights; adding a modifier will prevent the locker from locking. Interval: Inspect every oil change. Change at 45,000 miles if you frequently tow or drive in water/mud.

Brake Fluid

GM transitioned many of its half-ton trucks to DOT 4 brake fluid to support advanced trailering features and heavier payloads. DOT 4 has a higher boiling point than DOT 3, which is critical when braking down a steep grade with 10,000 pounds attached to the hitch. Common Pitfall: Brake fluid is hygroscopic (absorbs moisture). Never leave the cap off the bottle or the master cylinder. Flush the system every 3 years regardless of mileage.

Power Steering Fluid

The 2020 GMC Sierra 1500 utilizes an Electric Power Steering (EPS) rack. There is no power steering pump, no lines, and no fluid to check or top off.

Diesel Exhaust Fluid (DEF)

If you own the 3.0L Duramax, you will need to maintain your Diesel Exhaust Fluid. Use only DEF that meets the API certified ISO 22241 standard. Common Pitfall: DEF degrades over time, especially in high heat. Do not hoard DEF in a hot garage, and do not overfill the tank right before a harsh winter freeze, as the fluid is largely water and will expand when frozen.

Proper fluid maintenance is the cheapest insurance you can buy for your 2020 GMC Sierra 1500. Whether you are wrenching in your own driveway or taking it to a professional, ensuring these exact specifications are met will keep your truck hauling for years to come.

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