Im new to domestic cars, use to own import turbo cars. some how I fell in love with mustang after very bad car wreck, finally got a 1998 Ford Mustang GT 5 speed with 137k miles, when I bought the car I replace the radiator and recently fix all the code like 2 new 02 sensort, 180 T-stat, new plug, fix 1443 code, my car been loose alot coolant lately and never over heat before until I replace the 195 t-stat with 180 t-stat. when I ever I saw a low coolant light on, then the car idle and stumble, and sputing between 2 and 3 gears, but when I add more coolant or water, the car idle fine and smooth. the car is complete stock with that plastic intake manifold. What can I do to the car now ? i love this car and dont want let it go. thanks