Hi i have a 2002 chevy 2500hd 4x4. I keep having a problem with my coolant leaking out but i cannot figure out where its coming from. I pressure tested it and didnt lose any pressure so i left it on over night in the shop and came back in the morning and still holding strong and no water under truck. I changed the cap and when i start the truck i noticed coolant comes out of the overflow tube at a slow drip sometimes bit i wouldnt think thats enough to drain my coolant out. Any ideas.
thanks

 

are you overfilling the reservoir?

 

No and today i drove to work abd 4 hrs later i went to check the water and the reservoir had so much pressure the cap blew off when i unscrewed it. I was thinking the radiator is clogged. What do you think.

 

Is it overheating?

 

No its not over heating but after i drive for a few min the thermostat starts jumping from 205 down to 160 and right back up but doesnt go over 210 and today i drained all the coolant out and put flush in it to see if maybe the radiator is clogged and i also noticed that i have water coming out if my exhaust but i have no water in the oil it looks good.

 

Some water coming out of the exhaust is normal - it's condensation of the water formed from the process of combustion. You might want to check the compression of the cylinders to see if you have a bad head gasket. Identical readings in adjacent cylinders (like 1 & 3, 2 & 4, 5 & 7) can indicate a bad head gasket. Also, your posting about there being so much pressure in the expansion tank that it blew off the cap when you started unscrewing it is also a clue for a bad head gasket.

Good Luck!