1998.5-2002 Dodge 5.9L Cummins Cooling Parts

Cooling system parts on the 1998.5-2002 RAM 5.9L Cummins

The factory system on the 5.9L Cummins is straightforward. A Gates K080810 serpentine belt and 38175 tensioner drive the water pump and a viscous fan clutch, coolant moves through a crossflow radiator with a recovery bottle, and a thermostat decides when coolant heads to the radiator. The standard replacement list for these trucks is short: belts, water pumps, fan clutches, thermostats and radiator hoses. Up front, the radiator shares space with the intercooler, transmission cooler, A/C condenser and power-steering cooler, and the whole stack needs attention as mileage and power climb.

What fails and why

Hoses, the fan clutch and the radiator tanks are the age items on this generation. When one lets go, the risk is bigger than a roadside stop: overheating is one of the listed triggers for cracking the 1999-2001 '53' block, whose thin water-jacket walls can split below the freeze plugs on the passenger side. That crack can masquerade as a hose or heat-exchanger leak. If you keep replacing passenger-side hoses for a leak that comes back, look at the block, and on automatics look behind the transmission heat exchanger.

Chemistry is the other enemy of these parts. Mixing coolant families shortens the change interval for the whole system, and corrosion and water pump cavitation damage are the price of getting it wrong.

Stock replacement vs. upgrade

OE-style parts put the truck back to factory spec: Cummins Genuine thermostats, Dayco molded hoses and a Dorman thermostat housing go in where the originals came out. Upgrades make sense when you are already in there. The Mishimoto silicone hose kit replaces aged radiator hoses as a set, the XDP Xtra Cool water pump is an alternative to a stock-style pump, and the Mishimoto radiator and transmission cooler bundle handles two front-stack coolers in one job for trucks working harder than stock.

What we carry

• Thermostats and housings: Cummins Genuine 180- and 190-degree thermostats, Mishimoto high- and low-temperature thermostats, thermostat housings from Dorman and Wehrli Custom Fabrication, the Mahle water outlet and thermostat gasket, and the XDP thermostat housing bolt kit.
• Hoses: Dayco molded upper and lower radiator hoses and heater hoses, the Mishimoto silicone radiator hose kit, the Dorman heater hose assembly (heater core tube) and the Fleece Performance Engineering heater feed and return hose kit.
• Water pump hardware: the XDP Xtra Cool water pump, the XDP water pump bolt kit and the Mahle water pump seal.
• Sensors: the Cummins Genuine ECT sensor pigtail, the XDP ECT sensor and the Alliant Power oil/fuel/coolant temperature sensor.
• Front-stack coolers: the Mishimoto radiator and transmission cooler bundle and the CSF 10623 A/C condenser.
• Bypass and block parts: the Fleece coolant bypass service kit, replacement bypass O-ring kit and 34.5-inch Common Rail/VP44 bypass hose, plus the BD Diesel Killer Frost Plug Plate.

Fitment notes

Year ranges vary widely here, so read the fitment line on every listing. Some parts are specific to this generation, like the Cummins Genuine ECT sensor pigtail, the Dayco upper radiator hose and the Fleece heater feed and return hose kit, all listed for 1998.5-2002. Others run much wider, like the XDP ECT sensor (1998.5-2021). A few start later than 1998.5: the Cummins Genuine 190-degree thermostat is listed for 2000-2002, the Dorman heater core tube for 1999-2002 and the Dorman thermostat housing for 2000-2007, so an early truck needs a careful check. A 2002 Ram 2500 or 3500 still belongs here. Verify by VIN when a part is borderline.

Frequently asked questions

Which thermostat should I buy for my 24-valve?

Start with the year range. The Cummins Genuine 180-degree thermostat is listed for 1998.5-2007 and the 190-degree for 2000-2002, while Mishimoto's high- and low-temperature thermostats are listed for 1998.5-2013. Replace the Mahle water outlet and thermostat gasket at the same time.

Are silicone hoses worth it over molded rubber?

Both do the job. Dayco molded hoses are the OE-style route, one hose at a time, while the Mishimoto silicone kit replaces the radiator hoses as a set. Hoses on these trucks are age items, so on a high-mileage truck replacing them together makes sense.

I keep finding coolant on the passenger side. Is it a hose?

Maybe, but check the block before you buy another hose. On 1999-2001 trucks with a '53' block, cracks below the passenger-side freeze plugs leak coolant and can pass for a hose or heat-exchanger leak. On automatics, look behind the transmission heat exchanger.

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.