I have a small RV on a 3500 express chassis. I noticed a small coolant leak which only occurs when the engine is running. I located the leak and it appears to be coming from a tube that runs from the thermostate housing (I think) and disappears under the air intake. the tube is grey, metal and and about a quarter inch in diameter. Can anyone tell me what this is any how dificult it is to replace. The engine is a 2004b 6.0l, v8 and only has 9000 miles on it. Thanks in advance