I’m not a car guy. I want to be. I’m learning. I learn by making friends with mechanics and absorbing their information. I had a car a few months ago with some overheating issues. (Got it resolved. No water in my coolant at all, using straight concentrate in a brand new, empty radiator, like a dingus. 🤦🏼♂️) But before I fixed it, someone said it might have been the thermostat. I asked a mechanic friend of mine about it. (I haven’t known him long.) He told me he’s been a mechanic for right around a decade and has NEVER seen a thermostat issue cause overheating. Is he just totally out of touch? Or did I misunderstand how the cooling system of a vehicle works? Let me know.
Thermostats can fail in 2 ways.
They can fail open, which causes you to never get up to temperature. This isn’t good, but it’s not gonna risk catastrophic engine damage. Although your engine not getting up to temperature can accelerate premature wear, so it should still be fixed.
They can also fail closed. This is the one most people think of. Coolant simply can’t circulate properly and your engine overheats rather quickly. This is what causes bad head gaskets and the like if not spotted.
I’ve seen both types of failures multiple times, and had it happen to me once (failed closed in my case). It’s not implausible that he’s only seen failed opens, it’s just a bit strange.