COOLING SYSTEM — 03–07 DODGE RAM 5.9L CUMMINS

Fitment: 2003–2007 Dodge/Ram 2500 & 3500 with 5.9L 24-valve common-rail Cummins. Keep ECTs stable while towing, daily driving, or sled-pulling with proven radiators, thermostats, water pumps, fan clutches, hoses, and coolant bypass solutions from CPP Diesel.

• Shop All Cooling Parts — 03–07 5.9L
• Sensors / Electrical — 03–07

Popular Upgrades & Service Parts

• Radiators
  Mishimoto Aluminum Performance Radiator (R2711-MT)
  CSF 3710 OE-Replacement Radiator
• Thermostats
  Cummins 5292744 — 190°F OEM Thermostat
  Cummins 5292742 — 180°F Thermostat (performance/towing)
  Thermostat Category (including Mopar 05086739AB)
• Water Pumps
  Cummins 5473238 Genuine Water Pump
  All Water Pumps
• Fan Clutch & Controls
  CPP 55056990AC Electronic Cooling Fan Clutch
  Fan Clutch Connector Pigtail (68052582AB)
• Hoses & Heater Lines
  Dayco 72241 Lower Radiator Hose
  Fleece Heater Core Replacement Hose & Fitting (FPE-CUMM-HCL-0324)
• Coolant Bypass & Heat Exchanger Solutions
  Fleece Coolant Bypass Kit — 2003–2005 Auto
  Fleece Coolant Bypass Kit — 2006–2007 Auto
  Fleece Coolant Bypass Kit — 2003–2007 Manual
  Heat Exchanger Bypass Plug Kit (FPE-34382)
• Sensors & Monitoring
  Coolant Temperature Sensor (M-4954905)
  Engine Parts (Thermostat, Oil Cooler, etc.)
• Block/Frost Plug Solutions
  Cummins 3928341 Thread-In Block Heater (category list)
  BD “Killer” Rear Frost Plug Plate
  CPP Common Rail Expansion Plug Kit

Why Upgrade Your 5.9L Cooling System?

• Towing & Workloads: Larger-core radiators and healthy fan control keep temps in check on long grades.
• Longevity: Fresh water pump, correct-temp thermostat, and quality hoses reduce hotspots and pressure spikes.
• Consistency: Coolant bypass kits stabilize rear-cylinder temps—great for tuned and hard-working trucks.

Frequently Asked Questions

Which thermostat temp should I choose?

Most stock trucks do well with the 190°F OEM thermostat. If you tow heavy or run performance tunes, the 180°F option can help smooth temperature swings.

Do I need a coolant bypass kit?

It’s a popular reliability mod on 5.9L trucks to equalize temps at the rear cylinders. Choose the kit matched to your model year and transmission: 03–05 Auto, 06–07 Auto, 03–07 Manual.

My fan clutch is acting up—what should I check?

The electronic fan clutches on these trucks fail with heat and age. Replace the clutch (CPP 55056990AC) and fix damaged wiring with the correct connector pigtail.

Which coolant should I run?

Use a high-quality antifreeze that meets OEM specifications for your model year and climate. Many owners use HOAT/G-05 type coolant—always verify with your owner’s manual.

What are common water pump failure signs?

Coolant weep at the pump, bearing noise, or temperature creep at idle/light load. If present, replace with a genuine Cummins pump.

Cold-weather starting tips?

A thread-in block heater helps winter starts and warm-up. See the 03–07 engine parts list for the 3928341 block heater and cord.