My truck keeps leaking coolant out the over flow from what I can tell. I bought a block tester kit from Napa and test came back negative so no blown head gasket. Test the lines with pressure tester held pressure. Changed the cap on the surge tank went away for two weeks after that but now shows that I have low coolant again. Not smoking white out the exhaust. Can't see any leaks anywhere. I don't know. Any suggestions?

 

could be the water pump mine was leaking for months before i could tell where it was comming from the LB7s usually need a water pump at around 120000 miles..

 

also check the reservoir. mine actually had a small crack on the bottom that would let it slowly leak out

 

I talked with the dealership today about my truck leaking fluid very slowly and they didn't bat an eye in telling me that it was most likely the water pump... She said to start there!

Also, i noticed mine will sometimes leak down on the ground from the suspension lift (which is coming off the engine somewhere)

 

From what I read he's pressureizing the coolant. Not leaking the coolant. First off
the block tester you bought at napa most likely does not work on diesels, it might but usualy the ones they have on hand don't.

Does the truck over heat? Do you have heat in the cab when you come to an idle?
Is the upper radiator hose pressureized after leting the truck sit over night?