I recently bought an 06 Jetta TDI and I'm having some overheating issues I can't wrap my head around. I found the last owners receipt from a garage that replaced the egr cooler and still had issues when they returned the car. I checked the thermostat and water pump and both appear to function as normal. I did a few coolant flushes since there was an empty bottle of bars leak in the trunk and green coolant. Car will run normal temps till I get to a hill and then rocket to 250°. Pull over and check but the rad is ice cold and both hoses are hot. Reservoir appeared empty after I cracked it it filled to the top and then settle back down to the minimum mark. I pulled the radiator and tested it with the garden hoes and flows just fine. I bought a junk thermostat and took the guts out of it so flow wide open, this brings normal operating temperature down to 170 degrees but still pulls up to the to 230 to 240 on the same Hill. Fresh oil and air filter change. Does anyone have an idea where to start looking next.