Won't keep water in it please help

I have an 82 Subaru GL Sedan with 137,000 miles on it it has a 1.8 liter engine, automatic transmission I put antifreeze in it and it pushes it back through the reservoir. There is no water in the oil. I have flushed system completely with prestone back flush kit and it seemed to flow good. I put antifreeze in it and it is gone in 2-3 days. No visible leaks in radiator, hoses, or heater core. It has a brand new radiator cap as well. Does anyone have any suggestions on what could cause this?

How can you tell that heater core is not a suspect. If it leaks the coolant will end up inside of the air ducts and you will not see it right away. On another hand air ducts will not hold a gallon of antifreeze.

Antifreeze cannot disappear without a trace. If this is a head gasket - the oil level should at least rise. If this is a leak in the cooling system you should see antifreeze somewhere.

Another possibility is - you have air pockets in the system. In order to get rid of them you need to park on the hill nose up and open the radiator cap (make sure it is cold!). Run engine and add coolant little by little.

Good luck,

Sam

I would say you probably have a headgasket problem.

I will try thanks