White smoke from a 6.7L Cummins usually means unburned fuel or coolant entering combustion. On a cold start it is often the grid heater; if it persists or smells sweet, look deeper.
What causes white smoke on the 6.7L Cummins
- A weak grid heater on cold starts (white smoke until warm)
- Worn or leaking injectors (unburned fuel)
- A cracked EGR cooler leaking coolant (sweet white smoke, coolant loss)
- Low compression on a cylinder
How to diagnose it
Separate cold-only white smoke (grid heater) from persistent white smoke. Sweet-smelling smoke with coolant loss points to the EGR cooler; a raw-fuel smell points to injectors. Check grid heater operation and injector data.
The fix
Cold-start white smoke: service the grid heater. Fuel-smelling smoke: test and replace worn injectors. Sweet smoke with coolant loss: replace the EGR cooler and service the cooling system.
Frequently asked questions
Is white smoke on a cold 6.7L normal?
A little on a cold start that clears as it warms can be the grid heater. Persistent or sweet-smelling white smoke needs diagnosis.
Does white smoke mean a blown head gasket?
Not necessarily - on the 6.7L a cracked EGR cooler is a more common cause of coolant-related white smoke. Confirm before pulling the head.
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