Not a 318ti owner, but a 318i owner. I had the y-connector cause me some pain this week.
Long story short, I installed a defective thermostat. Which led to an overheat in the system and although I didn't blow my HG (mechanic said my compression levels were "on the money" but there could be a pinhole leak), the y-connector burst clean off.
I don't have the stomach to replace it myself so I forked over $300 in labor for my local mechanic to do it.
So, I can't endorse this PSA enough: REPLACE THESE PARTS!