1994-1998 Dodge 5.9L Cummins Cooling Parts

Cooling parts on the 1994-1998 Ram 5.9L Cummins

On the 12-valve 5.9L Cummins, the thermostat sits in a housing that feeds an upper coolant pipe and hose to the radiator, with a lower radiator hose closing the loop to the belt-driven water pump. Molded heater hoses carry coolant to and from the cab heater. The service parts on this system are the thermostat, hoses, fan clutch, belt and freeze plugs, plus the gaskets and seals that go with them. The genuine Cummins thermostats for these years are 180-degree units.

What fails and why

• Thermostat. A documented wear item. Slow warm-up or running hot are the signs.
• Upper hose and pipe. It is roughly 30-year-old rubber on these trucks. A soft, swollen or weeping upper hose needs replacing.
• Freeze plugs. They corrode and leak at the side of the block, and high coolant-jacket pressure on a performance engine makes it worse.
• Water pump. The other documented wear item. A weep from the pump vent or coolant loss you cannot trace elsewhere means it is wearing.

Stock replacement vs. upgrade

OEM-style is the normal path on this truck: genuine Cummins 180-degree thermostats, Dayco molded hoses, MAHLE gaskets and a Dorman thermostat housing put it back the way it left the factory. If you want more, there are options here. The Mishimoto silicone radiator hose kit replaces the molded rubber. Mishimoto's high- and low-temperature thermostats let you pick a different opening point than stock. The BD Diesel Killer Frost Plug Plate addresses freeze plugs, a known leak point on this block. Fleece Performance Engineering's Performance Coolant Bypass is built specifically for the 1994-1998 engine, with its own 39.5-inch bypass hose, a replacement O-ring kit and a service kit.

What we carry

From Dayco, molded upper, lower and heater hoses. From Mishimoto, thermostats, the silicone hose kit and radiator bundles. From Fleece Performance Engineering, coolant bypass kits, hose and O-rings. From MAHLE, thermostat, thermostat housing cover and water outlet gaskets plus a water pump seal. From Cummins, genuine 180-degree thermostats. Rounding it out: a Dorman thermostat housing, the XDP Xtra Cool water pump and the BD Diesel Killer Frost Plug Plate.

Fitment notes

Read the year ranges in the titles. The Dayco upper radiator hose changed in 1996: 71715 is listed for 1994-1995 and 71866 for 1996-1998. The lower hose, 71716, covers 1994-2002. Heater hoses carry their own ranges: 86815 for 1994-2002, 80400 for 1996-2004 and the 80402 heater outlet hose for 1994-2001 plus 2006-2009. The Mishimoto silicone hose kit and radiator bundles are listed for 1994-1997 only. 1998 is a split year, with the 24-valve ISB replacing the 12-valve partway through, so check for a P7100 inline pump with a mechanical shutoff solenoid (12-valve) or a VP44 rotary pump with a wiring harness (24-valve). Verify by VIN when in doubt.

Frequently asked questions

Which upper radiator hose fits my truck?

It depends on the year. Dayco 71715 is listed for 1994-1995 trucks and 71866 for 1996-1998. If you want silicone instead, the Mishimoto kit is listed for 1994-1997. A 1998 owner should confirm the engine first, since 1998 can be a 12-valve or a 24-valve.

Should I run the stock 180-degree thermostat or a Mishimoto high- or low-temp unit?

For most trucks, the genuine Cummins 180-degree thermostat keeps the engine at its factory setting. The Mishimoto high- and low-temperature versions are for owners who want a different opening point. Whichever you choose, put a new MAHLE gasket in with it.

What should I replace during the killer dowel pin job?

With the front of the engine apart, the common recommendation is to replace the belt and the hoses at the same time. Thermostat, fan clutch and freeze plugs are the other service parts on this system, so it is a good moment to look at them too.

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.