Filters
37 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) 722-5295Cooling system parts for the 2004.5-2007 RAM 5.9L Cummins
On the 5.9L Cummins, a belt-driven water pump moves coolant through the engine, the thermostat decides when it heads to the crossflow radiator, and a heater circuit feeds the cab. A large engine-driven fan on a viscous clutch pulls air through the radiator, intercooler and A/C condenser stack. The serpentine belt that turns the water pump runs off the harmonic damper pulley. The system holds about 7.3 gallons of coolant, factory-filled with Mopar HOAT to MS-9769 on 2003-2008 trucks. Most of the parts on this page are the smaller pieces of that loop: hoses, gaskets, sensors, housings and thermostats.
What fails and why
- Fan clutch. A viscous clutch can lose its silicone fluid, overheat its shear plates or seize. If the truck runs hot and the fan never roars, test it by hand with the engine off: light-to-moderate resistance is normal, none means fluid loss, absolute resistance means seized.
- Heater core and hoses. Topping off HOAT with green IAT can leave gummy deposits and restrict the heater core, and the silicates it drops can make the water pump weep.
- Belt alignment. A failing rubber harmonic damper throws off the alignment of the belt that drives the water pump.
- Water pump. The pump is on the 15,000-mile inspection list, so look at it whenever the truck is in for service.
Stock replacement vs. upgrade
For a straight repair, OEM-grade parts put the truck back to factory: Genuine Cummins thermostats, a Dorman thermostat housing and heater hose assemblies, Dayco radiator and heater hoses, and MAHLE gaskets and seals. If you want to go past stock, Mishimoto offers a silicone radiator hose kit alongside its replacement hose kit, plus high- and low-temperature thermostats. WCFab builds a thermostat housing and an upper coolant pipe, and Fleece Performance Engineering offers heater feed and return hose kits and coolant bypass parts. If you have no reason to change the thermostat's opening temperature, replace like for like.
What we carry
- Thermostats and housings: Genuine Cummins 180- and 190-degree thermostats, Mishimoto high- and low-temperature thermostats, Dorman and WCFab thermostat housings, MAHLE water outlet and thermostat gaskets, the Fleece M22 thermostat plug for cylinder heads, and XDP thermostat housing bolt kits.
- Hoses and pipes: Dayco upper and lower radiator hoses and molded heater hoses, Mishimoto hose kits, Dorman heater hose assemblies and heater core tube, the S&B heater core supply hose, Fleece heater hose kits and heater core replacement hose and fitting, and the WCFab upper coolant pipe.
- Coolant bypass parts: the Fleece coolant bypass service kit, replacement O-ring kit, 34.5-inch bypass hose and hose brackets.
- Water pump hardware and sensors: the XDP XTRA Cool water pump and water pump bolt kit, the MAHLE water pump seal, the XDP engine coolant temperature sensor and the Alliant Power oil/fuel/coolant temperature sensor.
- Radiators, condenser and more: Mishimoto radiator bundles and replacement radiator, the CSF A/C condenser, the BD Diesel Killer Frost Plug Plate, the Fleece upper fan idler for electric water pump setups, and the WCFab billet coolant tank cap.
Fitment notes
Year ranges matter here. The Dorman 626-321 heater core tube is listed for 2003-2005, the 626-574 center heater hose for 2006-2007, and the 626-660 L-shape heater hose for 2006-2009. The Dayco 80401 inlet hose covers 2000-2005, while the 80402 heater outlet hose is listed for 1994-2001 and 2006-2009, which skips 2004.5-2005 trucks. The CSF 10583 condenser is listed for trucks with a plastic-tank charge air cooler. It is commonly reported that 2005 trucks used plastic intercooler end tanks and 2006-2007 trucks went to metal, so look at your intercooler before ordering. Model year 2007 includes 6.7L trucks, and front-of-engine parts should be verified by engine rather than year. When in doubt, verify by VIN.
Frequently asked questions
Which thermostat should I buy?
This page has Genuine Cummins thermostats in 180- and 190-degree ratings and Mishimoto high- and low-temperature versions. Match the rating of the one you are replacing unless you have a reason to change it, and check the year range: the Cummins 190-degree part is listed for 2003-2007 5.9L and the 180-degree for 1998.5-2007 5.9L. Replace the gasket at the same time; MAHLE C31858 is listed for 2003-2007 5.9L trucks.
What causes a restricted heater core on these trucks?
One documented cause is mixed coolant. Topping off HOAT with green IAT can leave gummy deposits that restrict the heater core, and the silicates it drops can make the water pump weep. Drain the system, refill with HOAT rather than mixing, and replace tired heater hoses while you are in there.
Does the CSF condenser fit my truck?
The CSF 10583 A/C condenser is listed for 2003-2007 5.9L trucks with a plastic-tank charge air cooler. It is commonly reported that 2005 trucks used plastic intercooler end tanks while 2006-2007 trucks used metal, so check your intercooler tanks before you order.
My truck runs hot when towing. Where do I start?
Start with the fan clutch. With the engine off, spin the fan by hand: if it spins freely, the clutch has lost fluid, and that shows up as running hot towing or in traffic. If the fan never roars when the truck is hot, the clutch is the first suspect.
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.