I have a 1990 VW Golf Driver and topped up its coolant and oil before travel. After 1 hour driving, coolant started to come out of the system. There is also white chalky deposit on the new water pump. I don't know much about cars but but I checked for leaks and found a hole the size of a pin head in the oil tank (due to corrosion). Could this be the main prob or could it be the head gasket also. The car does not overheat and does not lose power.
Oil is black and there is no brown/white residue under oil cap or on dipstick. The hole in the oil tank leaks until a certain point, leaving just enough oil in tank.
Sounds like the gasket is ok, hole you found might be the only problem, but the white chalky deposit indicates a leak there so it is either the pump gasket not sealed properly, or possibly a leak from a loose pipe connection, is there a pipe above the pump?
I think the hole is in the sump (if that is the most lowest point of the engine), and not the oil tank. The chalky deposit around the pump seems to me that oxygen is getting in there somehow.