I was facing almost the same problem,but my case was the separator of oil and radiator water turned dead which resulted flow of Engine oil in my radiator,after some time my engine started eating engine oil and spoiling it all over the parts and started producing a lot of heat which affected the pick up of the car...So what we did was we changed all Rings Pistons of Engine installed clutch plates changed the Radiator(filled it with some branded coolant I don't remember the name "Tin wala Coolant") changed radiator pipes,fan wires etc...after the running we changed the engine oil (ZIC CNG 1750/=),Oil Filter,Spark Plugs wires,Gas Tuning etc and now it's running all COOL,I don't know If this might help you but these were the things which we did...I will suggest you to not use Water as a radiator coolant you should buy a branded coolant and always fill your radiator with the coolant,it does not evaporate shortly,it takes weeks and weeks to refill depends on your mileage.
Another strange thing which I encountered was my rear break shoes were touching the drum continuously while driving which resulted a pressure or Engine which resulted in over capacity on engine making it hot and which was eating all the pick up of the car,I suggest you to service your all tyre brakes shoes too,will cost you about 800 with new break shoes. hope it helps.