Common Cummins head gasket symptoms are coolant loss with no visible leak, white exhaust smoke, a pressurized or bubbling coolant reservoir, and overheating when towing or under heavy load. A combustion leak test, which checks the coolant for exhaust gases, confirms it. The usual causes are power increases that raise cylinder pressure beyond what the factory clamping can hold, overheating, and head bolts that have stretched.
Cummins head gasket symptoms
- Coolant level dropping with no external leak.
- White smoke with a sweet smell, especially at start-up; see diesel white smoke.
- Bubbles in the coolant reservoir, or hoses rock-hard when the engine is warm.
- Overheating under load; see engine overheating.
- Coolant pushed out of the overflow after hard pulls.
- Milky oil in severe cases.
How to test for a blown head gasket
- Combustion leak test. A block tester draws air from the radiator neck through a fluid that changes color if exhaust gases are present.
- Cooling system pressure test. A pressure drop with no outside leak points inside the engine.
- Cylinder leak-down test. Air escaping into the cooling system from one cylinder shows which part of the gasket has failed.
For the general signs on any engine, see signs of a blown head gasket.
Why Cummins head gaskets fail
- More power. Fueling and boost increases raise cylinder pressure, which can lift the head and push past the gasket.
- Head bolt stretch. Under repeated high pressure, factory head bolts can stretch and lose clamping force; see head studs vs head bolts.
- Overheating. Heat can warp the head or block surface.
What the repair involves
The cylinder head comes off. The head and block deck are checked for flatness and cracks, the head is machined if needed, and a new gasket goes on with new head bolts or head studs, torqued in the sequence and steps the service manual or stud maker specifies. Check the injectors, cooling system and turbo at the same time, and find the root cause, or the new gasket can fail the same way.
Repair or replace the engine?
If overheating has also damaged the block, or the engine is worn, a replacement long block can make more sense than a head gasket job. Options include the D&J Essential Long Block for 2007.5-2012 6.7L Cummins ($7,699.99) and the D&J Essential Long Block for 2004.5-2007 5.9L Cummins ($7,699.99). Check each listing for fitment and contents. See also 6.7 Cummins problems, 5.9 Cummins problems and Cummins engines.
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