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.
This is interesting and as a mechanic for the last 28 years I am going to give your friend some back up. I could not even come close to telling you how many times I have replaced failed open thermostats. I can tell you in that time span I have replaced less than 5 failed close and specifically only remember doing exactly 1. So for them to have never seen it is very possible. I will ask a few other techs today that will give decades possibly a century or two of experience and I would bet the total will be very low.
That said, I am not going to completely discard the comments from this who say they have seen many and is very common. The reason for that is this failure could be brand (vehicle or thermostat) specific. A brand that I do not use or see in the field often. I do recall seeing something about a Chrysler product that had a know stuck closed issue. I will ask today and let you know how often others I know have seen this. Should be entertaining.
I’ve had my shop for 13 years, and I too can’t remember the last time a car came in with a stuck closed thermostat. We’ve seen many stuck open thermostats, though. Just had one last week that wouldn’t set the cat monitor due to a partially stuck open tstat.
The other thing I don’t see as often anymore is rusted out cooling systems. Mostly due to the abundance of long life HOAT coolants and the like. I’m wondering if corrosive cooling systems were the major cause of tstas sticking closed, or if modern thermostats have been designed to fail open by default similar to the old safe-t-stats, or a mix of both.