Faulty cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages 
Refer to 
Diagnostic Starting Point - Engine Cooling
. 
Coolant consumption may or may not cause the engine to overheat. 
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- Inspect for spark plugs saturated by coolant. Refer to 
Spark Plug Inspection
.
 
- Perform a cylinder leak down test. Refer to 
Cylinder Leakage Test
 . 
 
- Inspect the cylinder heads and engine block for damage to the coolant passages and/or a faulty head gasket. Refer to 
Coolant in Combustion Chamber
 .
 
- Repair or replace, as required.
 
 
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