My 2000 Chevy 2500 6.5td started off blowing white smoke just on start ups now it does it all the time and low coolant light comes on but doesn't seem to be any leaks I can hear the gurgeling from the resovore also pulled the cap off the reservoir and its black. Oh and the temp seems good on the dash works like it should please help before I tear into it

 

From a cold engine-start the truck and then immediately check the pressure in the upper rad hose,if it gets hard/firm to being squeezed quickly you have compression getting into the cooling system.

Blown head gasket,cracked head or cracked block.