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Call or Text (352) 722-5295Cooling system on the 2007.5-2009 Ram 6.7L Cummins
A belt-driven water pump moves coolant through the block and head, through the EGR cooler, and through the water-cooled center section of the Holset turbo. It then runs to a large down-flow radiator with plastic end tanks, with a thermostatic fan clutch pulling air across it and a pressurized degas bottle handling expansion. The system holds about 5.7 gallons of Mopar 10-year/150,000-mile antifreeze mixed 50/50 with distilled water, and the factory flush interval is 97,500 miles or 60 months. The 6.7L Cummins replaced the 5.9L in mid-2007 and brought cooled EGR with it, so this system carries more heat than the 5.9L did. That puts the radiator, the water pump and the EGR cooler at the top of the service list.
What fails and why
- Radiator tanks. The factory plastic-tank radiator can crack at the tank seam under diesel heat and pressure, usually with age and miles. Watch for a weep at the top tank seam, a level that keeps dropping, and overheating when towing.
- Water pump. Aftermarket pump builders point to the factory pump's plastic impeller and small bearing. A leak from the weep hole or a bearing growl is the visible warning. A cracked impeller can overheat the engine with no external leak at all.
- EGR cooler. The EGR cooler's coolant hoses and fittings were revised for 2009, and recall 08V641000 covered a sagging engine silencer pad that could contact the EGR cooler on 2007-2008 trucks. Internal EGR cooler leaks are a known pattern on DPF-era diesels in general, though no 6.7L-specific failure rate is documented. Coolant loss with no external leak and white, sweet-smelling exhaust are the signs.
- Head gasket. It shows up as a cooling complaint first: the bottle overfilling, bubbles, or steam, most often after an overheat or after power has been added.
Stock replacement vs. upgrade
A stock-style part is the right call when the truck is near factory power and you want it back to spec: an OEM-style radiator, a genuine or equivalent water pump, a factory-temperature thermostat, molded hoses. Upgrades make sense when the truck tows hard or when the original part's design is the weak spot. The Mishimoto MMRAD-RAM-03 is all-aluminum and TIG-welded, with a 1.3-bar cap and a magnetic drain plug, so there is no plastic tank left to crack. Mishimoto's silicone radiator hose kit is the alternative to molded replacement hoses, and Fleece sells a coolant bypass for 2007.5-2012 trucks backed by its own service kit, O-ring kit and braided hoses.
What we carry
Mishimoto covers the most ground: aluminum and replacement radiators, radiator and transmission cooler bundles, high- and low-temperature thermostats, replacement and silicone hose kits, a top heater hose upgrade and Liquid Chill coolant. Fleece Performance Engineering supplies the coolant bypass service kit, bypass hose brackets, heater feed and return hoses and an M22 thermostat plug. Dayco brings water pumps and molded radiator and heater hoses. Dorman has the coolant recovery tank, a thermostat housing and heater hose assemblies. You will also find a genuine Cummins water pump and 190-degree thermostat, an Alliant Power water pump and temperature sensor, a CSF radiator and A/C condenser, Mahle gaskets and a water pump seal, an XDP coolant temperature sensor, bolt kits and a direct-fit radiator, a Wehrli Custom Fabrication thermostat housing, upper coolant pipe and billet tank cap, a stainless heater hose connector from Pacific Performance Engineering, an S&B heater core supply hose, and extended-life coolant from Hot Shot's Secret.
Fitment notes
Most radiators, hoses and coolers for this truck are listed 2003-2009 because the 5.9L and 6.7L share the third-generation chassis. Confirm the 6.7L-specific lower hose and the EGR coolant hoses, which changed for 2009, along with the water pump inlet housing. Some parts start at 2009, like Dorman's 626-572 inlet heater hose assembly. Some are 5.9L only, like Mishimoto's MMB-RAM-002 bundle; the 6.7L version is MMB-RAM-003. The 4500 and 5500 chassis cabs ride on a different chassis where most pickup parts do not interchange. When a listing splits years, verify by VIN.
Frequently asked questions
Why is my 6.7L pushing coolant out of the bottle?
Coolant pushed into or out of the degas bottle under load, with bubbles or steam, is the classic first sign of a head gasket on this engine. Replace the bottle if it is cracked, but find out why it is overfilling before you call the job done.
Is an aluminum radiator worth it over a stock replacement?
If your factory radiator cracked at the plastic tank, an all-aluminum radiator removes that failure point. Mishimoto's MMRAD-RAM-03 is TIG-welded, direct-fit for 2003-2009 trucks and comes with a 1.3-bar cap. For a near-stock truck in light duty, an OEM-style replacement from CSF or XDP gets you back to factory spec.
How much coolant does the 2007.5-2009 6.7L Cummins hold?
About 5.7 gallons. The factory fill is Mopar 10-year/150,000-mile antifreeze mixed 50/50 with distilled water, flushed at 97,500 miles or 60 months.
Do 5.9L cooling parts fit my 6.7L?
Many do. Radiators, most hoses and coolers are listed 2003-2009 because the chassis is shared. The 6.7L-specific lower hose and EGR coolant hoses differ, and 2009 changed the water pump inlet housing, so read the engine and year range in every title before you order.
What are the signs of a failing water pump?
Coolant from the weep hole and a growling bearing are the common outside signs. An impeller failure is harder to spot because it can overheat the engine with no leak at all. Treat any unexplained overheat as a reason to check the pump.
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.