I was wondering where exactly the thermostat is located on a 99 DII? Truck overheats, I have already done a radiator flush, it doesnt leak any fluid and my last resort is the thermostat. Thank you.

 

Look at the passenger side of your radiator follow the bottom hose up to the yellow plastic thermostat. Then it branches off to the water pump and to the top hose. It's a cheap repair, but you can remove it and boil it to test it.

 

Do you know how to bled the air from the coolant system? Have you already replace the upper radiator hose that now has a bleed screw in a black plastic tee, if not do that when replacing the t/stat.