OK So I have a 94 323 with 177,000 Khms on itas a winter beater, I replaced a few things like disty, plugs, wires, uper rad hose, mini rad hose off the block to some other steal line, Air filter. I work at a Mazda dealership so parts are very cheap for me! As I was getting on the Hwy I was up at about 110khms I was almost home about 15 khms away from work, I looked at my temp gauge and it was creeping up to HOT fast! So I turned the heat on full and got off the gas and it went back down to normal. This is the first time it happend! and Sometimes when I am driving normal roads I notice a little steam comming from the drivers side radiator area (this beaing why I replaced the hoses thinking pin hole leak) Now why did my gauge go up but drive fine and Idle fine when I was sitting at a light? Rad leaking?

 

From experience, if your temperature goes up, check or replace your thermostat. If your temp goes above 'Hot' to 'Really Friggin hot', you'll likely need to change the water pump and head gasket as well. When the thermostat goes, it sticks closed - predisposing you to overheating.

Are you loosing coolant? Could be radiator hose, could be a hole in the radiator core, could be a crack in the plastic on the top of the radiator... Need a better description of where you think the leak is coming from.