Help, please! Engine overheating 🥵

would you know, how long OEM coolant last if the can / jug is not opened?
I have 1 gallon sitting with for 2+ years
 
All good ideas, but I was just 2 miles from home, so not a situation on a hot day or long idle. The fan came on when I got it back home and reset the code.

I could have under-filled the radiator overflow when doing the 40k service. I don't think I have a leak (time will tell).

Sounding most likely that it's a bad temp sensor (pretty sure @Nashvegas had that issue) that is working intermittently.
 
Yep, “temperamental“ is exactly what it was. It didn’t matter what my coolant level was at the time. It would manifest itself when I got in traffic or start/stop in a small town. Open road was fine. Start it up, turn it off, start it up, turn it off, and it would sometimes start working again. It drove me nuts tracking it down. It is a little finned rectangular module right above the oil filter. Center/left if you are looking at the engine from the front. Kind of a pain to get to, but you have bled your clutch before so it should be no problem for you. I can get you the part number if you need it. But you will recognize it in a schematic. Has been working like a champ for a couple of years now.