I took the cruiser on about a 550-600 mile trip this weekend. This morning when I checked, my coolant reservoir was almost completely empty. I opened the radiator cap and it had coolant up to the top. Temperatures during driving were right at the halfway mark and never had a dash light for low coolant. Car currently has 221k miles and timing belt/water pump were done at 188k. I have been looking at some of the coolant leak threads and tried to check common spots and haven't found a leak. What I did find is this piece on the radiator was broken. Is this just a mounting piece or can coolant actually evaporate from this hole? First picture is the driver side and second is the passenger side which is not broken. It looks like the piece itself is part of the entire radiator so doesn't seem I could just replace it. If this is not the cause of the coolant loss, I guess I can do the coolant flush I was planning on doing and continue to monitor.