Vehicle is a 1987 560 SEL with 169000 miles. New timing chain, timing chain tensioner, and top three guide rails at 167000 miles (6 months ago).

While driving home from a short 5 mile trip I noticed the coolant temperature was up close to 100 degrees, so I stopped and topped off coolant reservoir with about 20 ounces of water. Now driving at 45 mph I notice the coolant temp rise up past 120 deg (red zone) in less then a mile. I drove another ½ mile to my house and let it idle, turned heater on high, opened the hood, and went to get some water. Took me 3-5 minutes to get some water and now the engine is making a LOUD KNOCKING noise.

It’s hard to pin point the exact location of the KNOCKING sound, but I’m 95% sure it’s coming from the engine on passenger side. I removed the passenger side cam/valve cover and everything looked normal, so I pulled the spark plugs and the plug closest to the firewall is wet and doesn’t look like it‘s been firing.

Does anybody know what the KNOCKING noise might be or have any suggestions on what I should do?