hey guys

i noticed that my top radiator hose is really really solid rock hard

first i thought it was just a simple radiator so i went to get a new one ( 0.9 bar )but it still doing it

took the car to a mechanic to get compression test and it turned to be all good
next was leak down test, it also came up good, no bubbles in the radiator

the car is not overheating or anything

its a built b18c block with darton sleeves

thanks in advance