Originally Posted by theonlypheonix

I don't mean to hi-jack this post but I've notice that my coolant has gone from a bright yellow in color to a brown color within the last 3K miles or so. This color change was rather sudden which is what concerns me the most. Up to this point I have been following Fords maintenance schedule closely and was considering doing the recommended 100K coolant change soon. But.....would anyone have an idea as whether this sudden color change could be an indication of head gasket failiure or just old tired coolant? I'm the original owner of the truck and it is an '05 F350 4X4 6.0L PS with babied 99,500 miles. As you can see because of the miles why I'm concerned about any potential head gasket failure. Is there a way to isolate head gasket failure vs old coolant, any type of lab test that can be done on the coolant? Other then this the engine runs great and there doesn't appear to be anything unusual with the engine oil (color ok and no loss between changes).