Originally Posted by Sniper
Gonna tell you right now, it's your electric water pump.

Overheating at speed is almost always a water flow issue.


This guy gets it!^^^ Overheating at speed is almost always a coolant flow issue....overheating at idle/low speeds is almost always an airflow issue. My guess is that electric pump is flowing the same at idle and 4000 rpm. Works at idle not at 4000 rpm. Belt drive pump changes output based on rpm. Just my thoughts. Good luck!