it would seem that the thermostat is stuck in the open position, allowing the coolant to circulate through the rad,instead of keeping it confinded to the block/head when cold,as
suspected above.
if you haven't changed one of these thermostats before you will be suprised by the look of it
as it isn't anything like a"normal" one.
i would suggest you try a search, as it needs to be "located" correctly,and be very careful
when tightening the housing (plastic),i believe,and is easily cracked apparently.
i haven't done one myself,i'm only going on what the forum members have shared in the past, which shows the value of the "search" facility.
regards,
stewy.