Faulty cylinder head gaskets and/or cracking or other damage to the cylinder heads and engine block cooling system passages. 
Coolant consumption may or may not cause the engine to overheat. 
 | 
|     •  | Perform a pressure test to the cooling system. Refer to 
Loss of Coolant 
 in Engine Cooling. |  
  
|     •  | Perform a cylinder leak down test. |  
  
|     •  | Inspect the cylinder heads and engine block for damage to the
 coolant passages and/or a faulty head gasket. |  
  
|     •  | Repair or replace as required. |  
  
 |