Filters
10 products
Not sure it fits your truck?
Our Wildwood, FL techs will confirm the right part for your build before you buy.
Call or Text (352) 722-5295Coolant on the 1989-1993 RAM 5.9L Cummins
The factory fill on the first-gen 5.9L Cummins is a 50/50 mix of ethylene glycol and distilled water, about 24-26 quarts in all. It circulates through the block, the radiator and the engine oil cooler, which shares the same circuit. The thermostat is rated at 180°F. Cummins pairs that coolant with a supplemental coolant additive, Fleetguard DCA4, unless you run Fleetguard's fully formulated extended-life coolant instead.
What goes wrong when coolant is neglected
Diesels are prone to cavitation. When the supplemental additive is neglected, you get pitting and corrosion: contaminated coolant, pinholes and, over the long run, erosion of the cylinder walls. Service guidance for this engine rates Fleetguard's extended-life coolant well ahead of the alternatives at preventing that pitting and wall erosion. The fix is not complicated. Use the right coolant, keep it treated, and change it on schedule.
Choosing a coolant
Start with the label. Check whether the product is pre-mixed or full strength, and whether it is sold as fully formulated for heavy-duty diesels or needs a supplemental additive alongside it. Pre-mixed coolant pours straight in. Full-strength coolant gets mixed 50/50 with distilled water. Then follow the interval: first change at 52,500 miles or 36 months, then every 24,000 miles or 24 months. Write down what you filled with so every top-off matches.
What we carry
- Mishimoto Liquid Chill: pre-mixed coolant in yellow and purple, Liquid Chill synthetic coolant, pre-mixed Liquid Chill synthetic, and the Liquid Chill radiator coolant additive.
- Hot Shot's Secret gallon jugs: 150K Mile Extended Life Green, 150,000 Mile Heavy Duty Extended Life Yellow and 750,000 Mile Heavy Duty Ultra Long Life Red.
- Lucas Oil 10640 Super Coolant.
Fitment notes
Coolant isn't year-specific the way hoses and radiators are, so most of these listings aren't tied to the first-gen. What you need to match is the chemistry and the quantity: roughly six gallons of 50/50 to fill the system from empty. If you're replacing a water pump, thermostat or heater core lines, you'll be refilling anyway, so that's the time to switch products and start the interval clock over.
Frequently asked questions
How often should I change the coolant in a 1989-1993 Cummins?
The schedule calls for the first change at 52,500 miles or 36 months. After that, change it every 24,000 miles or 24 months. Keep a note of the date and mileage so the next one doesn't slip.
Do I still need DCA4 with these coolants?
Cummins calls for a supplemental additive such as Fleetguard DCA4 unless the coolant is fully formulated, with Fleetguard's extended-life coolant as the named example. Check each product's label for heavy-duty diesel formulation. If it doesn't say, call us before you fill.
How much coolant do I need for a complete refill?
The system holds 24-26 quarts, about six gallons, mixed 50/50 with distilled water. Pre-mixed products are ready to pour, so buy enough for the full volume. With a full-strength product, roughly half that volume is coolant and half is distilled water.
Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.