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Call or Text (352) 722-5295Coolant for the 2003-2004 Ram 5.9L Cummins
The Cummins in these trucks runs a big cooling system. Published capacity ranges from about 7 gallons to 32.7 quarts (30.9 liters), so plan on roughly 7 to 8 gallons of mixed coolant for a full drain and refill. The factory spec is Mopar 5-year/100,000-mile HOAT antifreeze mixed 50/50 with distilled water, and the change interval is 100,000 miles or 5 years. Coolant is the easiest part of the cooling system to keep right, and it matters. Overheating is listed as a crack contributor on 24-valve Cummins blocks, and the coolant is what carries that heat out to the radiator.
Choosing a coolant
Start with what is in the truck now. If you know the system still has the factory-style HOAT fill and it is inside its interval, top off with a product whose label says it is compatible. If the history is unknown or the interval has passed, a full drain, flush and refill puts you back on a known baseline. Pre-mixed products are ready to pour. Anything sold as a concentrate gets mixed with distilled water to the 50/50 the factory called for. Extended-life products are rated by the maker for a certain service life, so read the label rather than assuming every coolant runs the same distance. Write down what you put in, and the next person who works on the truck will know where to start.
What we carry
Mishimoto Liquid Chill covers the most ground here: pre-mixed Liquid Chill coolant in yellow and purple, Liquid Chill synthetic coolant, a pre-mixed synthetic version and a Liquid Chill radiator coolant additive. Hot Shot's Secret sells coolant by rated life in 1-gallon jugs: a 150K-mile extended-life green, a 150,000-mile heavy-duty extended-life yellow and a 750,000-mile heavy-duty ultra-long-life red. Lucas Oil Super Coolant rounds out the shelf.
Fitment notes
Coolant is not tied to a model year the way a water pump is, and most of these products do not list one. The fit question is chemistry. These pages are for the Ram 2500 and 3500 (sold as Dodge Ram) with the 5.9L, and the factory reference is Mopar HOAT. Check the product page for compatibility before you mix anything with what is already in the truck. If you are refilling after a water pump, radiator or hose job, buy enough for the whole system rather than a top-off quantity.
Frequently asked questions
How much coolant does a 2003-2004 Ram 5.9L Cummins hold?
Sources disagree a little. One lists about 7 gallons, and another lists 32.7 quarts (30.9 liters). Plan on roughly 7 to 8 gallons of 50/50 mix for a full drain and refill.
How often should I change the coolant?
The factory interval for the Mopar 5-year/100,000-mile HOAT fill is 100,000 miles or 5 years. If you switch to a different product, follow the service life printed on its label instead.
Can a coolant additive replace a coolant change?
No. An additive goes in with coolant; it does not stand in for a change. Use the Mishimoto Liquid Chill radiator coolant additive alongside a healthy fill that is inside its interval, not as a fix for coolant that is past due.
Not sure which coolant fits your truck? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.