Coolant leak

[cameyer]

ok so here is the issue, i have a 64 k10 with a 327 from a 68 c20 and i am losing coolant out of the overflow tube like crazy. I have checked the oil and no coolant seems to be making it in there and the oil cap is clean so I dont think it would be the head gasket but i dont know what else it could be. The truck isnt overheating at runs at a normal temperature but i will fill the coolant up drive a few mile to the store mike up some groceries come back outside and find a puddle of coolant under the truck. None of the hoses are leaking and i cant see any obvious leaks other than the coolant draining from the over flow tube. anyone have any ideas?