2018 Ram 2500 Fluid Type Specifications: The Complete Reference

The 2018 Ram 2500 is a heavy-duty powerhouse, available with a 5.7L HEMI V8, a 6.4L HEMI V8, or the legendary 6.7L Cummins Turbo Diesel. Because this truck is designed to tow, haul, and work hard, maintaining the exact factory fluid specifications is absolutely critical. Using the wrong coolant, transmission fluid, or oil weight can lead to catastrophic component failure, expensive repairs, and voided warranties.

As an ASE-certified master technician, I always stress the importance of following the OEM (Original Equipment Manufacturer) specifications. Below is your complete, comprehensive fluid guide for the 2018 Ram 2500.

Quick reference

Fluid	Type/Spec	Capacity (Approximate)
Engine Oil (5.7L V8)	5W-20 API SN, Mopar MS-6395	7.0 Quarts (with filter)
Engine Oil (6.4L V8)	0W-40 Synthetic, Mopar MS-12633	7.0 Quarts (with filter)
Engine Oil (6.7L Cummins)	10W-30 or 5W-40 Synthetic, API CK-4, MS-10902	12.0 Quarts (with filter)
Engine Coolant	Mopar 10-Year/150k OAT (Purple), MS-90032	18.3 qts (5.7L), 16.6 qts (6.4L), 29.5 qts (6.7L)
Automatic Transmission (66RFE / 68RFE)	Mopar ATF+4, MS-9602	5.5 - 6.5 Quarts (Service Drain & Fill)
Automatic Transmission (AS69RC Aisin)	Mopar ASRC, MS-9224	7.2 Quarts (Service Drain & Fill)
Manual Transmission (G56)	Mopar ATF+4, MS-9602	5.5 Quarts
Transfer Case (BorgWarner)	Mopar Transfer Case Fluid (BW44-44) or ATF+4	Approx. 2.0 Quarts (Verify in owner's manual)
Front Differential (AAM)	75W-90 Synthetic GL-5	Approx. 2.5 - 2.8 Quarts
Rear Differential (AAM)	75W-90 or 75W-140 Synthetic GL-5	Approx. 4.0 - 4.2 Quarts
Brake Fluid	DOT 3 (MS-3111)	Fill to MAX line
Power Steering	Mopar Power Steering Fluid +4 (MS-9602)	Fill to MAX line
Washer Fluid	Standard All-Season Windshield Washer Fluid	Up to 1 Gallon
DEF (6.7L Cummins only)	API Certified DEF, ISO 22241	5.5 Gallons

Note: Capacities are approximate. Always fill to the proper dipstick mark, fill plug hole, or reservoir line.

Engine Oil Specifications

The engine oil requirements for the 2018 Ram 2500 vary drastically depending on the engine under the hood.

• 5.7L HEMI V8: Requires 5W-20 engine oil that meets Mopar MS-6395 standards and API SN or higher. The Multi-Displacement System (MDS) relies on this exact viscosity to activate and deactivate cylinders properly.
• 6.4L HEMI V8: This higher-output engine requires a fully synthetic 0W-40 oil meeting Mopar MS-12633. Ram specifically recommends Pennzoil Ultra Platinum. Never use a thicker oil, as the Variable Valve Timing (VVT) and MDS systems are highly sensitive to oil pressure and flow.
• 6.7L Cummins Diesel: For ambient temperatures above 0°F, you can use 10W-30. However, for extreme cold or heavy towing, a fully synthetic 5W-40 meeting API CK-4 (and Cummins CES 20086 / Mopar MS-10902) is highly recommended.

Technician Pitfall: Do not skip oil filter changes, and always use a premium filter (like a Fleetguard or Mopar). For the Cummins, failing to keep up with CK-4 oil changes can lead to soot build-up, turbo bearing wear, and premature DPF (Diesel Particulate Filter) clogging.

Engine Coolant (Antifreeze)

For 2013 and newer Ram trucks, FCA switched to OAT (Organic Additive Technology) coolant. The specific spec is Mopar MS-90032, and it is distinctly purple in color.

Technician Pitfall: Never, under any circumstances, mix OAT (purple) with HOAT (Hybrid OAT, orange/pink, used in 2012 and older Rams) or standard green ethylene glycol. Mixing OAT and HOAT creates a gel-like sludge that will rapidly clog your heater core, radiator, and engine block coolant passages. If you are ever in doubt about what is in your truck, perform a complete chemical flush.

Transmission Fluid

Your transmission fluid spec depends entirely on the transmission your truck is equipped with:

• 66RFE (Gas) and 68RFE (Diesel): These Chrysler-built transmissions require Mopar ATF+4 (MS-9602). Never use universal "multi-vehicle" ATF in these units. The clutch friction materials are specifically engineered for the friction modifiers in ATF+4.
• AS69RC (Aisin 6-speed): Available on high-output Cummins models, this commercial-grade transmission requires Mopar ASRC (AS68RC) fluid (MS-9224). Do not put ATF+4 in the Aisin transmission.
• G56 Manual Transmission: Interestingly, the manual transmission uses ATF+4, not standard heavy gear oil.

Transfer Case Fluid

Ram 2500s equipped with 4WD use BorgWarner transfer cases. Depending on whether you have an electronic shift or manual shift transfer case, it will either take standard ATF+4 or a specific Mopar BorgWarner Transfer Case Fluid (MS-10216). Always consult your owner's manual or local dealer using your VIN to confirm which case you have, as putting ATF+4 into a case designed for the specific BW fluid can cause premature chain wear.

Differential Gear Oil (Front & Rear)

The 2018 Ram 2500 uses American Axle Manufacturing (AAM) solid axles front and rear.

• Front: 75W-90 Synthetic GL-5 gear oil.
• Rear: Depending on the engine and towing package (10.5-inch or 11.5/11.8-inch ring gear), it will take either 75W-90 or 75W-140 Synthetic GL-5. 140-weight is typically recommended for heavy towing.

Technician Pitfall: A massive misconception with the AAM axles is the need for a limited-slip friction modifier. The Ram 2500 AAM axles use a helical-gear limited-slip differential (Anti-Spin), which does not utilize clutch packs. Therefore, no friction modifier additive is required.

Brake Fluid

The factory specification for the hydraulic brake system is DOT 3 (MS-3111). DOT 4 can be used as an upgrade due to its higher boiling point, which is excellent for heavy towing down steep grades. However, remember that DOT 4 absorbs moisture faster than DOT 3, meaning you will need to flush the brake fluid more frequently (every 2 years). Never use DOT 5, as it is silicone-based and will destroy the ABS module.

Power Steering Fluid

Heavy-duty Rams still use hydraulic power steering (often hydro-boost systems that also assist the brakes on diesel models). Use Mopar Power Steering Fluid +4, which is essentially ATF+4 (MS-9602).

Diesel Exhaust Fluid (DEF)

If you drive the 6.7L Cummins, your truck is equipped with an SCR (Selective Catalytic Reduction) system requiring DEF. You must use DEF that is certified to ISO 22241 standards (API certified).

Technician Pitfall: DEF degrades when exposed to heat and sunlight. If you don't drive your truck often, buy DEF from high-turnover stores (like truck stops) rather than auto parts stores where it might have been sitting on a shelf for a year. Bad DEF will trigger a countdown on your dash and eventually limit your truck to 5 MPH.

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