1991 Ford Fairlane DAILY WATER USAGE ENGINE ALWAYS HOT

Hi there
i noticed my car keeps running hot and have been topping u the water but it has got worse and most days I have to ut in 2/4litres of water and if I go on ong journey have to top that up again so sometimes 8 litres water, I had a mechanic look at it and he changed the water pump and pipe (charged me loads) but I still have the problem I also have changed the thermostat which is keeping the needle down a bit more on the temp gage but still not working, any ideas what the problem could be? Also now if I go over 1800 revs the car starts to bunny hop a bit altho im not sure if that is a seperate problem with the gas system