A lot of plastics melt around 350-550 degrees, so I’d be removing it, pronto.  Also, the last thing you need is something accumulating debris INSIDE the engine — a plugged rad is annoying, but kinda’ functional whereas a plugged engine is disastrous.  I’d remove it and not think twice.  My guess is same as yours — preventing foreign object intrusion for shipping or such.  Though most I’ve seen use a solid orange cap with lip for that purpose…

Based on what you are describing, you are looking into the top water fitting where the hose connects ? Looking down into this there is generally a thermostat in this housing..  If possible take a digital picture and either post it of forward it to us and we will do our best to steer you in the right direction.

Thanks GV @ Apex

978-479-7974

apexkart@comcast.net