Hi, My name is ***** ***** for the delay.
I will do my best to assist you.
from the way you explain the problem,to me it sounds as if you do maybe have a blown head gasket,it would seem the compression from an cylinder is blowing into the coolant chamber,thus equilizing the pressure and stopping the coolant from moving.
if the pressure gets above the rating of the radiator cap[maybe 12lbs] then it blows the coolant out then overheats.
even if no fan was working it shouldnt overheat out on the road sense it would be getting plenty of air.
try bleeding the system this way,it may have an air pocket,if it still pushes back though the cap after this,i would think it is the head gasket
1-remove the radiator/reservoir cap when the engine is cold
2-start the engine and let idle
3-turn the heater on max
4-keep coolant on hand and add it as needed
5-spme coolant may gush out with the air
6-keep doing this until the engine is at operating tempeture and the heater is hot
7-after the coolant settles down and the engine is warm,,install the cap
This may take as long as 20-30 minutes