help! radiator hose was pinched!!!

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hi there - i'm hoping to get some help with an overheating issue (i've read lots of posts but not sure if any match my issue...). i'm driving a 1993 w124 (300ce).

i replaced the thermostat about 2 months ago to fix a previous cooling issue and it worked like a charm..

now it seems like the issue is back again, so yesterday i popped the hood open and noticed that the pipe that goes from the radiator to the thermostat (circle in pic) was pinched shut, obviously from some kind of vacuum created internally!!!

after about 30 mins the vacuum went away but i also turn the car on (not the engine just to the first key stop).

appreciate to hear your ideas on what this could be!