I am going today to check out friends 05 duramax he said that coolant changed color and smels realy bad.He replaced water pump and flushed coolant a week ago and it coolant changed color to dark again.(That is what he said) He is leaning towards the head gaskets but i never seen coolant change color with head gasket problem.I am leaning towards egr cooler myself,but will have to check it out.
Please help any sugestion or opinion is apriciated at this point. Truck has 130000 and runs good and strong with no power problem