I put a rebuilt 5.4 in a 2006 F150 and it has a coolant leak. The coolant starts to drip from the 2nd bolt back on the left side valve cover. You can actually see it puddling up between the head and valve cover with a mirror. Nothing appears to be getting in the oil. The other really odd thing is that if you pressure test the cooling system the drip is really slow. If you actually start the truck the drip is much faster. Anybody ever hear of or see anything like that? The owner of the truck is going to call the re-builder Monday. By the way a 5.4 3 valve engine replacement on a 4X4 F150 is a nasty job. I hope I never have to do another one.