Shop Cooling System by Category
Filters
45 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 on the 1998.5-2002 RAM 5.9L Cummins
The layout is conventional. The serpentine belt (a Gates K080810 with a 38175 tensioner) turns the water pump and a viscous fan clutch, and coolant runs through a large crossflow radiator with a recovery bottle. Automatic trucks add a transmission heat exchanger on the block. The system holds about 6 gallons (24 qt), and a normal drain and refill takes 5 to 5.5 gallons. The 5.9L Cummins block is parent-bore cast iron with no wet sleeves, so liner cavitation is not a worry and the engine needs no supplemental coolant additives (SCAs).
Up front, the radiator shares the front stack with the intercooler, transmission cooler, A/C condenser and power-steering cooler. All of them need attention as mileage and power climb, not just the radiator.
What fails and why
Most cooling trouble on this truck is age: hoses, the fan clutch and radiator tanks. The serious one is the '53' block. Blocks cast by TUPY in Brazil for 1999-2001 carry a '53' casting number and thin water-jacket walls that can crack below the freeze plugs, usually on the passenger side. Diesel Hub lists unexplained coolant loss, a wet block and overheating under load as the symptoms. On automatics the leak often hides behind the transmission heat exchanger, where it is easy to mistake for a hose or heat-exchanger leak.
Overheating is itself one of the triggers for that crack. A tired fan clutch, a plugged radiator or a low coolant level is doubly expensive here, so if the temperature climbs when you tow or pull a grade, find the cause before it becomes a block problem.
Chemistry is the quieter failure. Topping off with a different coolant family drags the whole system down to the shorter-life coolant's change interval, and in Valvoline's test an OAT coolant run in a HOAT-designed system damaged a water pump. Many owners also report power-steering fluid running very hot on these trucks, dark and burned with hose fittings too hot to touch; TDR members solved it with an add-on cooler.
Stock replacement vs. upgrade
For a truck that mostly hauls and commutes, OE-style parts are the straight answer: a direct-fit radiator, a genuine or OE-style water pump, the factory-temperature thermostat and new molded hoses restore the design the truck left the plant with. Upgrade when the front stack is being asked to do more. Upgraded radiators, transmission coolers and condensers are catalogued for 1994-2002 Cummins trucks, and a silicone hose kit replaces aged rubber in one job. If the power-steering side runs hot while towing, a cooler in the return line is the fix TDR members used.
What we carry
- Radiators: Mishimoto aluminum and replacement radiators plus a radiator essentials bundle and a radiator and transmission cooler bundle, the XDP Xtra Cool direct-fit radiator, and an OEM-style replacement from CSF, which also supplies an A/C condenser for this truck.
- Water pumps: Dayco, Cummins Genuine and Alliant Power pumps and the XDP Xtra Cool pump, plus Mahle water pump seals and XDP water pump bolt kits.
- Thermostats and housings: Cummins Genuine 180- and 190-degree thermostats, Mishimoto high- and low-temperature thermostats, a Dorman thermostat housing, an XDP housing bolt kit and the Mahle water outlet and thermostat gasket.
- Hoses: Dayco molded upper and lower radiator hoses and heater hoses, the Mishimoto silicone radiator hose kit, a Dorman heater core tube assembly and the Fleece Performance Engineering heater feed and return hose kit.
- Sensors: the Cummins Genuine ECT sensor pigtail, the XDP ECT sensor and the Alliant Power oil/fuel/coolant temperature sensor.
- Coolant and the rest: Mishimoto Liquid Chill coolants and additive, Hot Shot's Secret extended-life coolants, Lucas Oil Super Coolant, the Dorman recovery tank, Fleece coolant bypass kits and the BD Diesel Killer Frost Plug Plate.
Fitment notes
This page is for the 24-valve trucks: 1998.5 through 2002 Dodge Ram 2500 and 3500, filed under RAM in our navigation. A 2002 Ram 2500 or 3500 still belongs here even though the 2002 Ram 1500 moved to the next generation; the 2003 HD trucks are a new platform. Many parts carry wider ranges in their titles (the water pumps are listed 1989-2012), but others are narrow, so read the years on every listing. Thermostats are the classic example: the Cummins Genuine 190-degree unit is listed for 2000-2002 and the 180-degree unit for 1998.5-2007. Use the 24-quart capacity for this truck, not the 26 quarts of the 1994-1998 12-valve or the 29.5 quarts of 2003-2008 trucks. When a part is borderline, verify by VIN.
Frequently asked questions
How can I tell if my truck has a '53' block?
Look on the side of the block for '53' in the casting. These blocks were cast by TUPY in Brazil for 1999-2001 and have thin water-jacket walls. If yours has one, check the passenger side below the freeze plugs for coolant, and on automatics look behind the transmission heat exchanger.
What coolant goes in a 1998.5-2002 5.9L Cummins?
The factory fill was green low-silicate ethylene glycol meeting ASTM D-4985/GM 6038M. TDR recommends Chrysler MS-9769 HOAT as a backward-compatible replacement once the green is drained out. Pick one family and stay with it; the block needs no SCAs.
Why does my 24-valve keep losing coolant with no obvious leak?
Check the hoses and the recovery bottle first, then the block. On 1999-2001 '53' blocks, a crack below the passenger-side freeze plugs leaks coolant and is easy to miss, especially behind the transmission heat exchanger on automatics. Unexplained coolant loss and a wet block are the classic signs.
Do I need an upgraded radiator on a stock truck?
Not by default. A direct-fit replacement restores the factory design. Upgraded radiators earn their place as power and towing loads climb, because the whole front stack works harder, and since overheating can crack a '53' block, a marginal radiator should not stay in service.
Which thermostat temperature should I run?
Start with the year range on the listing. The Cummins Genuine 180-degree thermostat is listed for 1998.5-2007 and the 190-degree for 2000-2002, and Mishimoto offers high- and low-temperature thermostats listed for 1998.5-2013. If you are not sure which your truck needs, call the shop and we will check it.
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.