I have 95,000 miles, 4cyl, 2.0 L. The car was overheating so I added 50/50 engine coolant. I used half of the container. 5 days later, it started to overheat again so I added the other half. Now 5 days later, which is now, it started to overheat again. The engine fan comes on, there does not appear to by any leak. I added it to the overflow tank. Should I be adding the coolant directly to the radiator? Could there be anything else be wrong?