Hello , i picked up a 2002 Altima from a friend of mine . All seemed well but i noticed a couple days after i got it that the upper radiator hose would go almost flat after i turn the car off and it would sit for about 10 mins or so . I made sure the overflow tube was clear and replaced the radiator cap and bled the air out --- which fixed that issue .

Now , after fixing that , i been watching the car alittle better and noticed the lower radiator hose stays quite cold and the upper hose is hot . The heat seems to work fine and it doesnt appear to be overheating . Ive not driven the car very far out of concern of the lower hose being much much cooler then the upper . After reading i see there are 2 thermostats , If one is the issue , would it be the lower one since the lower hose is staying cool ?

Welcome to Nico!

I would certainly start at that other thermostat. Is it at the lower hose on the block? I'm not familiar with this platform, but it should be cooler at the lower hose if your radiator is working. While you've got the coolant out, remove your radiator and backflush it with a garden hose to clean that out a bit.

Good luck.