the rpoblem is the bottom bolt hole for the thermostat houseing just keeps on turning, never gets tight. tried putting it on as tight as itl go but water absolutly pisses out

i live in the middle of nowhere and the closest garage i would take the car to is 15 miles away, cant drive the car and cant repair it!!!

tried tapping the hole but it dont work, any ideas on how to fix it??
someone mentioned HELICOIL kit the other day but spoke to the guy at my local parts place and he says you cant just buy one, they come in a big kit costing £300!!!!

please help me!!!! if theres anyone who lives in the borders and could fix it ill sort em out!!!!!!!!!