I thought the engine was 5 years or 100,000 miles? Unless the truck was bought late in 99, your out of warranty.

 

It is the engine warranty. You can crawl under the passenger side to see the crack. With the hood open generally you can see the freeze plug that is for a different location of a turbo drain and it will collect coolant in it that can be seen from above.

Best way would be to have a garage pressure test the system and while under pressure, crawl under and look for a leak in that area.