I have 2001 Nissan Xterra SE 3.3L V6. A few weeks ago my car started to overheat while going through the grapevine (mountain pass in SoCal). After filling it up with coolant, I took it to the shop. They couldn’t figure out what exactly was the problem. It passed the block test and such. They said the top hose was swelling up as if something was blocking it. They also said my car was going through about a gallon of coolant. They replaced the water pump, thermostat, and the top hose. they also replaced the timing belt.
After driving the car for an hour, it started to overheat again. This time, I took it to the Nissan dealership. They said the timing belt was off by 2 teeth and they think that’s why it overheated, so they fixed that problem. They also did a cooling system test and found no leaks.
I got the car back and it still overheats. After the turn off the car, I see coolant being bubbling back into the reservoir almost to the top.
Also, my radiator was replaced about a year ago.