The phrase "upper radiator" refers to the top portion of a cooling system in a vehicle. It is responsible for circulating coolant or water to cool down the engine. Full definition
The dash gauge indicates and upper radiator hose gets hot but radiator doesn't boil I removed lower hoses and nothing is coming from water pump (mechanics.stackexchange.com)
Beneath the two upper radiator grille crosspieces, there are four additional bars. (greencarcongress.com)