1989-1993 Dodge 5.9L Cummins Radiators

The radiator on the 1989-1993 RAM 5.9L Cummins

The radiator on a first-gen 5.9L Cummins sits in a stack. From mid-1991 an air-to-air intercooler shares the same airflow. On automatic trucks, the factory air-to-oil transmission cooler sits in front of the radiator, fed from a heat exchanger on the passenger side. Behind the radiator, a viscous fan clutch on a bearing-mounted hub pulls air through all of it, speeding up as the air off the radiator gets hotter. The system holds about 24-26 quarts of 50/50 coolant, with a 180°F thermostat controlling flow.

Before you replace the radiator

Overheating doesn't always mean the radiator. On these trucks, check two things first. A viscous fan clutch that has lost its fluid spins with very little resistance by hand and won't pull air at low speed, so the engine runs hot in traffic or when towing slowly. A thermostat stuck closed also overheats the engine. If both check out and the radiator itself is the problem, replace it.

Stock replacement vs. upgrade

The Mishimoto MMRAD-RAM-89 is the upgrade route documented for these trucks. It's an all-aluminum, two-row radiator with a 2.2-inch core, a 1.3 bar cap and a magnetic drain plug, listed as a direct fit for 1991-1993 D and W trucks with the 5.9L Cummins.

What we carry

The Mishimoto MMRAD-RAM-89 Aluminum Performance Radiator, listed for 1991.5-1993 Cummins trucks. A new radiator means a coolant refill, so it's also a good time to reset the coolant clock: the first change is due at 52,500 miles or 36 months, then every 24,000 miles or 24 months.

Fitment notes

Mishimoto lists this radiator for 1991-1993, and our listing reads 1991.5-1993, the intercooled trucks. Vendors don't always mark the mid-1991 change the same way, so go by what's in front of your radiator, not by the year in the title. Owners of 1989-1990 trucks should verify fitment with us before ordering. On automatics you'll be working around the factory transmission cooler mounted ahead of the radiator. The fins are easy to damage, so handle the new core carefully.

Frequently asked questions

Will the Mishimoto radiator fit a 1989 or 1990 Dodge Ram Cummins?

Mishimoto lists it for 1991-1993, and our listing covers the 1991.5-1993 intercooled trucks. Fitment on the earlier non-intercooled trucks isn't confirmed, so call the shop before you order for a 1989-1990.

What are the specs on the Mishimoto MMRAD-RAM-89?

It's an all-aluminum radiator with a two-row, 2.2-inch core. It's specified with a 1.3 bar radiator cap and has a magnetic drain plug.

Should I pull the radiator for the killer dowel pin job?

It's optional, but recommended. The KDP tab job on 12-valve engines puts you at the front gear housing, and the fan and shroud have to come out together. The radiator fins are easily damaged, so pulling the radiator protects it, and it's a natural time to replace an old one.

My truck overheats towing at low speed. Is it the radiator?

Check the fan clutch first. A viscous clutch that has lost its fluid won't pull air at low speed and spins with little resistance by hand. A thermostat stuck closed is another cause. Replace the radiator once those are ruled out.

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.