Short answer
Towing up long grades is the hardest work a pickup does, and it exposes any weakness in the cooling system. The common causes are simple: debris packed between the intercooler, A/C condenser and radiator; a fan clutch that is not engaging; low coolant; a sticking thermostat; or a tired water pump.
Start with the easy checks
- With the engine cold, look between the stacked coolers for bugs, dirt and leaves.
- Check the coolant level and condition (cold engine only).
- Note whether the fan roars when the engine is hot. A viscous fan that never engages is a clue.
- Know what your gauge is reading: coolant temperature and exhaust gas temperature (EGT) are different.
Likely causes, most common first
- Blocked cooling stack
- Debris between the coolers cuts airflow.
- Fan clutch
- Fan drive makers publish checks for viscous clutches that do not lock up when hot.
- Low coolant or a leak
- See the coolant loss guide.
- Thermostat or water pump
- A thermostat that does not open fully or a weak pump.
- Load, gearing and grade
- Heavy loads at low speed on long grades create the most heat.
These are common causes, not a diagnosis. The same symptom can have a different cause on your engine; codes, tests and your service information decide.
For Ram towing setups
Cooling is the engine side. If the truck also squats, sways or wanders with a load, that is suspension and front end. Dodge Off Road offers air bag systems for 3rd and 4th gen Rams and 2nd gen Rams, plus traction bars. Verify fit and your truck's ratings before you tow.
When to stop and see a diesel tech
- The gauge climbs fast or hits the red.
- Coolant loss or white smoke.
- Overheating continues after cleaning and fan checks.
Questions
Is it EGT or coolant temperature that I should watch?
Both matter, but they measure different things. Coolant temperature is the cooling system; EGT is exhaust gas temperature. Follow your owner's manual guidance for each.
What should I do if my diesel overheats while towing?
Ease off, let the engine cool under the guidance in your owner's manual, and never open a hot radiator or reservoir cap.
Related symptoms
My diesel is losing coolant with no visible leak. Why?
Troubleshoot →CoolingHow do I know if my 6.0 Power Stroke EGR cooler is failing?
Troubleshoot →Power & drivabilityWhy did my diesel lose power or go into limp mode?
Troubleshoot →Where this comes from
- Ross Airworks service bulletin: viscous fan drive diagnosis (PDF)
- Manufacturer bulletin filed with NHTSA: high/low engine coolant temperature diagnosis
- CumminsForum: Overheating while towing (owner thread)
- BD Diesel: Duramax LLY/LBZ common issues
Last reviewed 2026-10-19. General information only: confirm with your service information and a qualified diesel technician.