Maybe a dumb/odd question, but this am I checked my coolant level in my header tank (plastic) and it seemed ok, but then I thought about it and said, hmmm, I thought I used to see a red plastic insert right below the cap. I went to my basement and checked my old cracked tank that I replaced in the fall, and sure enough, there was the red plastic insert in the old tank. I pulled out the temperature sending tube and looked inside and sure enough, there was that insert floating inside - pulled it out with a pick and it looked like it melted and got distorted and then dropped in the tank. Ok, so after all my rambling, does this piece have any use or can I just leave it out. Oh and no my S4 did not overheat or anything, running just fine, temps around 85-90 on the gauge.