Losing heat after driving 2016 Rogue

[loadandgorogue25]

Got this used Rogue a few months back. The heat works well when I first start it up, but then it fades after about 20 km on the highway. I've noticed that the top radiator hose gets hot, while the bottom one stays cold. I've already switched out the thermostats thinking they were the problem. There's no overheating happening by the way. Has anyone else experienced this?

 

[Crikey]

Well the cold lower hose kinda makes me think it's a clogged radiator or bad water pump. Maybe try to pressure test it just to be sure there's no hidden blockage messing with your flow.