2015 Ram 3500 Coolant Capacity & Type: A Complete Guide

The 2015 Ram 3500 holds between 18.3 quarts (17.3 liters) and 31.1 quarts (29.5 liters) of coolant, depending entirely on which engine is powering your heavy-duty truck. When it comes to maintaining a workhorse like the Ram 3500, understanding your cooling system is absolutely critical to preventing catastrophic engine failure, especially when towing heavy loads up steep grades.

Quick answer

Here is the essential information you need before servicing the cooling system on your 2015 Ram 3500:

• Total cooling system capacity: 18.3 to 31.1 quarts (17.3 to 29.5 liters), depending on the engine.
• OEM coolant spec: Mopar 10-Year/150,000 Mile Formula OAT (Organic Additive Technology). It is Purple in color and meets Chrysler material standard MS-12106. Never mix this with the older orange/pink HOAT coolant used in pre-2013 Ram trucks.
• Mix ratio: 50/50 mixture of OAT concentrate and distilled water, or a pre-mixed 50/50 OAT coolant. In extreme cold climates (below -34°F), a 60/40 coolant-to-water ratio can be used, but never exceed 70% antifreeze.

Capacity by engine option

Because the 2015 Ram 3500 was offered with three distinct and massive engines, the fluid requirements vary significantly.

Note: Capacities are approximate and include the heater core and coolant recovery bottle. Vehicles equipped with auxiliary cabin heaters or dual radiators (common on high-output Cummins models) may require slightly more fluid.

Flush interval

For both the Hemi V8s and the Cummins diesel, the factory-recommended flush interval for Mopar MS-12106 OAT coolant is 150,000 miles or 10 years, whichever comes first under normal driving conditions.

However, for a 1-ton truck operating under severe duty (frequent heavy towing, excessive idling, fleet use, or extreme ambient temperatures), I highly recommend inspecting the coolant strength and condition every 50,000 miles. If you notice any discoloration, debris, or a drop in pH levels, flush the system early to protect the water pump and engine block.

How to refill & bleed

Properly bleeding the cooling system on these heavy-duty trucks, particularly the 6.7L Cummins, is vital. Air pockets can lead to localized boiling, blown head gaskets, or EGR cooler failures.

1. Drain the system: With the engine cold, open the petcock at the bottom of the radiator. Remove the radiator cap to speed up draining.
2. Refill: Close the petcock. Slowly pour the 50/50 mixed OAT coolant into the radiator until it reaches the neck. Fill the coolant recovery reservoir to the "COLD MAX" line.
3. Bleed the V8s (5.7L / 6.4L): Leave the radiator cap off. Start the engine and turn the cabin heater to maximum heat and blower speed. Let the engine idle until the thermostat opens (the upper radiator hose will get hot). Top off the radiator as air bubbles burp out. Replace the cap.
4. Bleed the 6.7L Cummins: The Cummins engine requires extra care due to the EGR cooler and complex routing. While you can burp it manually by removing the air bleed plug near the EGR cooler during the initial fill, using a vacuum cooling system filler is highly recommended. A vacuum fill tool pulls a deep vacuum on the entire system, verifying there are no leaks, and then completely fills the block, radiator, and heater core without introducing a single air bubble.
5. Final check: Drive the truck through a few hot/cold heat cycles and recheck the reservoir level in the morning when the engine is completely cold.

Common cooling system issues

As an ASE master tech, I see a few recurring cooling system issues on the 2013-2018 generation of Ram 3500s:

• Water Pump Failures (6.7L Cummins): The factory water pumps on the 6.7L are known to develop leaks at the weep hole or suffer from bearing failures around the 75k-100k mile mark. If you smell sweet coolant near the front of the engine, check the pump immediately. There was also a recall for a specific batch of water pumps that could overheat and pose a fire risk.
• Radiator Y-Pipe Leaks: The plastic coolant Y-pipes on the Hemi models often become brittle from heat cycling and crack, leading to sudden coolant loss. Upgrading to aftermarket aluminum Y-pipes is a popular and permanent fix.
• EGR Cooler Leaks (6.7L Cummins): If you are losing coolant on your diesel but cannot find an external puddle, the EGR cooler may be leaking internally. This sends coolant into the exhaust, creating white smoke out the tailpipe and risking severe engine damage.
• Wrong Coolant Mixed: Adding older MS-9769 HOAT (Orange/Pink) coolant to the factory MS-12106 OAT (Purple) coolant will create a thick sludge that clogs the heater core and radiator. Always double-check your bottle!

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