2018 Ram 2500 Coolant Capacity & Type

The 2018 Ram 2500 holds between 18.2 quarts and 29.5 quarts of coolant depending on which engine your truck is equipped with. As an ASE-certified master technician, I can tell you that keeping the cooling system in top shape on these heavy-duty trucks—especially the 6.7L Cummins—is absolutely critical to preventing expensive engine and emissions component failures.

Whether you are hauling heavy loads across the country or just performing routine driveway maintenance, using the correct coolant type and knowing your exact capacity is vital.

Quick answer

• Total cooling system capacity: 18.2 to 29.5 quarts (17.2L to 28.0L), depending on the engine.
• OEM coolant spec: Mopar 10-Year/150,000 Mile Formula OAT (Organic Additive Technology). The Mopar specification number is MS-12106. The factory color for this coolant is Purple.
• Mix ratio: 50/50 mixture of OAT concentrate and distilled water, or a pre-mixed 50/50 OAT coolant. Never use tap water, as the minerals will cause scaling inside the radiator and engine block.

Warning: Do NOT mix OAT (Purple) coolant with the older HOAT (Orange/Pink) coolant used in pre-2013 Ram trucks. Mixing them causes a sludgy gel that will clog your heater core and radiator.

Capacity by engine option

Because the 2018 Ram 2500 was offered with three very different powerplants, the cooling system capacities vary significantly. The 6.7L Cummins has a massive cooling system to handle extreme towing and EGR cooling demands.

Note: Capacities are approximate. Always buy an extra gallon of 50/50 mix to account for system variations and future top-offs.

Flush interval

Modern OAT coolants are designed to last a long time, but heavy-duty trucks often see severe duty cycles that shorten fluid life.

• Normal Duty: Flush and replace the coolant every 10 years or 150,000 miles, whichever comes first.
• Severe Duty: If you frequently tow heavy trailers, idle for extended periods, or drive in extreme heat or dusty conditions, I recommend dropping that interval to every 5 years or 100,000 miles.

How to refill & bleed

The 6.7L Cummins and the HEMI V8s require careful bleeding to prevent air pockets, which can cause localized overheating or damage to the EGR cooler on the diesel.

1. Drain the system: Make sure the engine is completely cold. Open the petcock valve at the bottom corner of the radiator and drain into a large catch pan.
2. Vacuum fill (Highly Recommended): For the 6.7L Cummins, using a vacuum coolant refill tool (like an AirLift) is strongly recommended. This tool pulls a vacuum on the entire cooling system and sucks the new coolant in, eliminating air pockets in the dual radiators and EGR cooler completely.
3. Manual fill (If no vacuum tool): Slowly pour the 50/50 Mopar MS-12106 OAT coolant into the radiator until it reaches the neck. Fill the coolant reservoir to the "COLD MAX" line.
4. Bleed the V8s: The 5.7L and 6.4L HEMI engines have a bleeder screw located on the water pump housing/thermostat housing. Open this screw slightly while filling until a steady stream of coolant comes out, then tighten it.
5. Burp the system: Leave the radiator cap off. Start the engine and turn the heater to maximum heat and low fan. Let the truck idle until it reaches operating temperature (the thermostat opens). Top off the radiator as air bubbles escape.
6. Final check: Replace the cap, test drive, let the engine cool completely, and check the reservoir level again.

Common cooling system issues

The 4th generation Ram HD trucks are generally robust, but there are a few cooling system weak points to watch out for:

• Water Pump Failures (6.7L Cummins and 6.4L HEMI): The water pumps on these engines are known to develop leaks at the weep hole or suffer from bearing failures. Listen for a squealing pulley or look for purple crust around the front of the engine block.
• Radiator End Tank Leaks: The crimped seams where the aluminum radiator core meets the plastic end tanks can separate over time due to chassis flex and thermal cycling, leading to slow leaks.
• Y-Pipe Coolant Leaks (HEMI): The plastic Y-pipes in the heater hose assembly can become brittle and crack, dumping coolant abruptly. Many owners upgrade to aftermarket metal Y-pipes.
• EGR Cooler Leaks (6.7L): If you are losing coolant in a Cummins but can't find an external leak, the EGR cooler may be leaking internally, sending coolant into the exhaust.

If you suspect a leak or need a professional coolant flush, don't ignore it—especially if you haul heavy. Find a trusted shop on Repairius.