Engine Cooling problem
1997 Mazda Protege 4 cyl Front Wheel Drive Manual 300xxx miles

I have a problem with my 1997 mazda protege.Last summer i was driving in the highway and when i stopped in the gasoline station i smelled something. and when i moved my car an old lady told me that there's a lot coolant under my car. so i checked and i saw my coolant resrvoir. it was full and i don't remember putting that much coolant on it. so what i did is i took some water from the washroom and put it on my radiator.i also drained the reservoir to the right amount it suppose to have.so when i went on to where im suppose to go i checked it again.and i saw the coolant coming out from my reservoir. so i put another one.i asked my friend who knows a bit about cars.he said its not bad cause the oil and water is not mixing. So after a week i used it to go for a long drive (3 hours drive) i brought a lot of bottled tap water with me in case i might need them and i did. So i still reached my destination. We rented a cottage there and stayed there for 2 1/2 days so i didnt use it for 2 1/2 days. but when we're going back home after 2 hours of driving on the highway i just noticed my temperature is going up to the edge so i stopped and pulled my car on the side. and the engine is smoking. my friend who knows a bit about cars was with that time he helped to cool down the engine. we took the inside road. and the temperature will rise again. so i just figured how to drive.i have to switch the gear immediately. so i was able to reach home. then i was still able to use it for a week but driving it like that way(switching gears immediately) i brought to some mechanics.and they diagnosed it first.He also drained and flushed my radiator. he said some parts of my radiator is cold and some are not while running. it went well for a while.so i thought its ok now.and i was able to drive up to my place without shifting immediately and not overheating.but when i reached my house i saw the coolant coming out from my reservoir again.He told me to buy this powder (prestone) that seals leaks in your cooling system. but it didnt work. so i went to another mechanic. he said its only the thermostat. so he replaced it and after that its still the same. so he said it might be there's crack on my head cylinder or my head cylinder gasket is blowned. and they said its gonna cost me like 900 bucks so i said no thanks. i began to think maybe that's why the powder(prestone) didnt work.but still there's still few left powders inside the engine. and still didnt work. so i dont how am i gonna fix my car now?can you help me guys?its been in my garage for 5 months now. i jsut want to fix it and sell it.i already bought a new car.i was thinking it might be the water pump or the head cylinder gasket. because a year ago when i bought that car. there was a leak on the water pump. i replaced the water pump. the water pump that i bought has different holes for the screw so what my mechanic friend did is he improvised by drilling some holes on it so it will fit on my engine. and it did.so im thinking that it must be that. and i was also hearing sound like there's something loose somewhere there.i was thinking it might be the water pump when the idle is high. we just ignored because it's not making any problem at all. and i was still able to use it for year. and im also thinking that it might be the head cylinder gasket because my mechanic friend who replaced the water pump told me that i might need to replace the gasket after a few months because he already opened my engine so oil might leak out there or it might create air pockets..i dont know what's really the problem please help me..i tried opening it.its just hard especially its a DOHC engine.