I need help with a coolant overflow to the overflow chamber in the reservoir without the vehicle overheating. The hoses are new, I replaced the cap, the water pump is new and the thermostat looks new (its about a year and a half old). First I thought the thermostat was reversed yet I checked and its ok yet after 5 minutes with the engine running the overflow chamber slowly starts to accumulate coolant. I have no idea what can be causing this issue. Has anyone had this issue and how to solve it please? Remember, there is no overheating; the temperature gauge stays slightly under the middle.