Bought a used 2010 nissan murano with 130k miles. Had her for 2 weeks with no issues. Took her for a drive over 45 miles today and she started to overheat. It was all highway. When I noticed it overheating I slowed down considerably and she cooled a little. I tried turning off the AC and it didn't help much. Messed with the ac a couple times and it dropped the temp for a few seconds than the temp kicked back up. When I came to a complete stop the temp went back to normal and stayed normal. I checked the overflow container and the coolant was backed up and full into the container. After I shut the vehicle off the coolant slowly drained from the container. What the heck is going on? Please help.