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Call or Text (352) 722-5295Coolant for the 2004.5-2007 RAM 5.9L Cummins
From 2003 through 2008 these trucks were filled at the factory with ethylene-glycol HOAT to Chrysler spec MS-9769, which looks pink to orange. Some 2003-2005 trucks came off the line with green IAT coolant instead, so a 2004.5 or 2005 truck may never have had HOAT in it. Run it 50/50 with distilled water and plan a flush every 100,000 miles or five years. A normal drain-and-fill takes about 6.5 gallons of the 7.3-gallon total. Because the 5.9L Cummins is a parent-bore block with no wet sleeves, it does not need the SCA cavitation treatment that sleeved diesels depend on.
What goes wrong
The coolant problem to avoid on these trucks is mis-service. Topping off HOAT with green IAT drags the whole system down to the shorter-life interval, about two years instead of five, and the mix can drop silicates that abrade the water pump shaft seal. The signs are gummy deposits, a restricted heater core and a weeping water pump. Pouring the 1998.5-2002 low-silicate green spec into a third-gen truck is the same mistake from the other direction, since 2003-2008 trucks call for HOAT.
Choosing a coolant
Start with what is in your radiator now. If it is HOAT and in good shape, top off with the same chemistry. If you find green coolant, or you don't know what is in the truck, MS-9769 HOAT is backward-compatible, so drain it and refill instead of mixing. Go by the specs printed on the label, not by the color in the jug. Pre-mixed coolant saves you buying distilled water; concentrate lets you set the 50/50 mix yourself.
What we carry
- Mishimoto Liquid Chill coolant in pre-mixed yellow and purple, Liquid Chill synthetic coolant in full-strength and pre-mixed form, 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 fits any engine physically; what matters is chemistry. Compare each product's listed specs against MS-9769 before you top off, and flush first if you are changing types. This page is for the 5.9L. The 2007 model year also includes 6.7L trucks built after January 1, 2007, so confirm your engine. When in doubt, verify by VIN or call the shop.
Frequently asked questions
Can I top off with whatever coolant I have on the shelf?
Not if it is a different chemistry. Mixing green IAT into HOAT cuts the interval to the shorter-life coolant, about two years, and can drop silicates that wear the water pump seal. Match what is in the truck, or do a full drain and refill.
How much coolant do I need for a flush?
The system holds about 7.3 gallons (29.5 quarts), and a normal drain-and-fill takes about 6.5 gallons. If you buy concentrate, mix it 50/50 with distilled water. Pre-mixed coolant goes straight in.
My truck has green coolant. Is that wrong?
It may be original, because some 2003-2005 trucks shipped with green IAT. The spec for 2003-2008 trucks is HOAT MS-9769, and HOAT is backward-compatible. The fix is to drain the green and refill with HOAT rather than mix the two.
Does the 5.9L need a cavitation additive?
No. The block is parent-bore with no wet sleeves, so SCA treatment for liner cavitation is not required. The Mishimoto Liquid Chill product on this page is sold as a radiator coolant additive, not an SCA.
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.