6.7 Cummins Cooling System Modifications: Complete Guide
Posted by Hunter on Apr 07, 2026
6.7 Cummins Cooling System Modifications: Complete Guide
The 6.7L Cummins is a strong, capable engine — but its cooling system has well-documented weak points that affect both high-mileage trucks and performance builds. The stock system is adequate for a bone-stock truck driven conservatively, but it was not designed with compound turbos, aggressive tunes, or 200,000-plus-mile commercial use in mind.
This guide covers the 6.7 Cummins cooling system from the ground up — how it works, where it fails, what modifications are worth making for different use cases, and what Diesel Power Source® components address the most common failure points directly.
How the 6.7 Cummins Cooling System Works
The 6.7L Cummins uses a pressurized liquid cooling system with a coolant pump driven off the front of the engine. Coolant circulates through passages in the block and head, absorbing heat from combustion, before passing through the radiator where that heat is transferred to ambient air. A thermostat controls coolant flow to maintain operating temperature — on the 6.7L this is typically around 190 to 200 degrees Fahrenheit under normal conditions.
Beyond the basic engine cooling circuit, the 6.7L uses coolant in two additional systems that create their own failure points. The turbocharger is water-cooled — coolant lines run to and from the turbo bearing housing to prevent heat soak after shutdown. The EGR system on emissions-equipped trucks also uses a coolant-fed EGR cooler to reduce the temperature of recirculated exhaust gas before it re-enters the intake.
These additional circuits — particularly the EGR cooler and its associated plastic coolant components — are where most 6.7L cooling problems originate.
Common 6.7 Cummins Cooling System Problems
Plastic Coolant Riser Pipe Failure
The most notorious cooling system failure on the 6.7L Cummins — particularly on 2013–2018 trucks — is the plastic coolant riser pipe at the top rear of the engine. This OEM plastic component is exposed to extreme heat cycling and is prone to cracking, which results in coolant loss, overheating, and white smoke from the exhaust. It is a known failure point that has affected a significant number of 4th gen trucks. On modified trucks where engine bay temperatures run higher than stock, the failure rate increases.
EGR Cooler Failure
The EGR cooler on emissions-equipped 6.7L trucks circulates coolant through a heat exchanger that cools recirculated exhaust gas. Over time and high heat cycles, the internal tubes in the EGR cooler can crack or fail, allowing exhaust gas to enter the coolant system or coolant to enter the intake. Symptoms include white smoke from the exhaust, unexplained coolant loss, and in severe cases, coolant contamination of the oil. EGR cooler failures are more common on trucks used for heavy towing and on high-mileage examples.
Coolant Line Degradation
The rubber and plastic coolant lines throughout the 6.7L system — including those serving the turbo and EGR system — degrade over time from heat cycling and age. Lines that are original on trucks over 150,000 miles are worth inspecting carefully, particularly at connection points where cracking initiates. A failed coolant line to the turbo is especially problematic because it can cause heat soak in the turbo bearing housing after shutdown, accelerating bearing wear.
Coolant System Pressure Loss on Modified Trucks
On trucks running compound turbos, aggressive tunes, or other performance modifications, under-hood temperatures run higher than stock. This additional heat accelerates degradation of plastic coolant components and can cause coolant loss through the path of least resistance — typically the plastic riser pipe or aging hose connections. Modified trucks benefit significantly from proactive coolant system upgrades before failures occur.
6.7 Cummins Cooling System Modifications Worth Making
Coolant Riser Pipe Delete and Reroute (2013–2018)
For 2013–2018 Ram 2500 and 3500 trucks that have had the EGR system deleted, the Diesel Power Source® 6.7 Cummins Coolant Reroute Kit eliminates the failure-prone plastic riser pipe entirely and replaces it with steel braided and silicone hose, machined fittings, and a new aluminum coolant tank. This kit addresses the single most common cooling failure point on the late 4th gen 6.7L while also cleaning up the engine bay after EGR removal.
The kit includes a complete coolant tank assembly, new aluminum coolant tank, high-pressure safety cap, tank level sensor, steel braided reroute hose, silicone coolant hoses, and all fittings and hardware. It also relocates the coolant tank to clear space for compound turbo kits and 3rd gen swap installations — making it a practical requirement for many performance builds on 2013–2018 trucks.
It is important to note this kit is designed for trucks that have already had the EGR system deleted. It is not compatible with the stock EGR configuration, and Diesel Power Source® does not provide EGR delete components.
Turbo Coolant Line Replacement
The turbo coolant lines on the 6.7L serve the critical function of circulating coolant through the turbo bearing housing to prevent heat soak after shutdown. On high-mileage trucks and on trucks where the turbo has been upgraded, inspecting and replacing these lines is a worthwhile maintenance step. Upgraded lines with better fittings and more durable hose material reduce the risk of a coolant loss event at the turbo — which can cause significant bearing damage if the turbo is shut down hot without coolant circulation.
Coolant System Flush and Maintenance
The 6.7L Cummins uses OAT (Organic Acid Technology) coolant that has a service life of approximately 150,000 miles or 5 years. On trucks approaching or past this interval, a system flush and fresh coolant significantly reduces the risk of corrosion-related failures in the cooling passages and EGR cooler. This is particularly important on trucks used for heavy towing where the cooling system operates near its capacity regularly.
EGR Cooler Inspection on High-Mileage Trucks
On emissions-equipped 6.7L trucks with over 150,000 miles, an EGR cooler inspection is a worthwhile preventive measure. Early-stage EGR cooler failure can be caught through a combustion gas test of the coolant — a relatively inexpensive procedure that detects exhaust contamination before it becomes a more serious problem. Addressing the EGR cooler proactively is significantly less expensive than dealing with a coolant system contamination event.
Thermostat Replacement on High-Mileage Engines
The thermostat on the 6.7L is a wear item that is often overlooked at high mileage. A thermostat that is sticking open causes the engine to run below optimal temperature, affecting fuel economy and combustion efficiency. One that is sticking closed or slow to open causes overheating, particularly under load. On trucks past 150,000 miles, replacing the thermostat with a quality OEM-spec unit is inexpensive insurance against temperature management problems.
Cooling System Modifications for Performance Builds
For 6.7L Cummins trucks running compound turbos, aggressive tunes, or both, the stock cooling system components are not adequate for the long term. The increased under-hood temperatures and higher sustained loads demand more durable components in the cooling circuit.
The priority order for a performance-built 6.7L is as follows. First, replace the plastic coolant riser pipe with the steel and aluminum reroute kit if the EGR has been deleted — this is the highest-failure-risk component and should be addressed before any other cooling modification. Second, replace the turbo coolant lines with upgraded lines that can handle higher under-hood temperatures without degradation. Third, ensure the cooling system is filled with fresh coolant at the correct concentration — a neglected coolant system on a performance-built truck is a reliability problem waiting to happen.
These modifications address the actual failure points in the 6.7L cooling system rather than adding cooling capacity that the stock system already has in adequate supply for most applications. The 6.7L does not typically need a larger radiator or high-flow water pump for street and towing use — it needs its weak stock components replaced with more durable alternatives.
Cooling Modifications by Generation
Not all 6.7L cooling system recommendations apply equally across all model years. Here is a generation-specific breakdown of the most relevant modifications.
2007.5–2012 (4th gen early): The plastic coolant riser failure is less prevalent on earlier 4th gen trucks, but turbo coolant line inspection is still worthwhile at high mileage. EGR cooler inspection becomes relevant past 150,000 miles.
2013–2018 (4th gen late): The plastic riser pipe failure is most common on this generation. The coolant reroute kit is the highest-priority modification for deleted trucks in this range. Turbo coolant lines and EGR cooler inspection apply here as well.
2019–present (5th gen): Coolant system design was updated for the 5th gen. The specific plastic riser failure is not the same issue on these trucks. Standard maintenance — coolant flush intervals, turbo coolant line inspection, and thermostat replacement at high mileage — applies.
