Okay here's a new problem I've never heard of: this morning on the way to work (temp in high 80s), while sitting at a red light the temp gauge in my '53 Chevy started going DOWN. Generally it'll go down the road all day long at 190 degrees no matter what the weather, and when it's close to 100 out the temp will very slowly creep up at a red light with the A/C on, but today the temp went from 180 to maybe 160 just in the half-mile from the traffic light to my workplace. I was running late or I'd have driven around longer just to see what would happen. Any idea what is up with that? My thoughts are: failing gauge, failing sending unit, or failing thermostat but I've never had a thermostat stick OPEN?? I won't really know what's up until I drive home at 5:00 today but if something is getting hinky I'd like to figure it sooner than later.
Well they do stick open, I got on in the garage that is stuck open, the spring also breaks on occaision. But there are a lot of variables here, start with the simple stuff and work your way out. For instance, you can turn the switch on and pull the wire off your sender then ground it. if it goes to hot you can rule out the temp gauge.
Make sure its not out of water! I've seen the gauge go down when a hose busts or something, the gauge wont read right if its not covered in water.
Yes, they do stick open. I had one in a daily do that - first it stuck closed, then it opened and stayed and I never noticed until a few months later when it got cold enough I wanted some heat - and had no heat. The temporary cure was some cardboard in front of the radiator; you might be able to try that and see if the temp comes up. Sometimes the temp sender can go bad, too - some Chevy engines have the thing on the left side front on the head, if the wire dangles and touches a manifold it can melt and screw it up. That's probably unlikely on your car but worth mentioning.
Well that's two things I can do before I even leave the parking lot. Thanks, guys! I'm pretty sure it's not out of water (no obvious leaks, and the upper hose was hot like normal) but it'll be easy enough to find out when I walk out to the car. If a thermostat can fail in the open position then that is my guess. That'll be pretty easy to diagnose, too. I've only had them stick closed - this is much better in my opinion! Any brand recommendations if I do end up replacing the thermostat? I've got NAPA, Autozone, and O'Reilly all within a couple miles of my house. (Last time I bought a "name brand" thermostat it turned out to be made in CHINA!)
I don't know how true what I was told is, but the last one I bought the counter person told me that they are made to stick open when they fail verus sticking shut nowadays......
Buy a cheap infrared remote temp tester or borrow one before you go too far. It could be just a failing sending unit or gauge. A thermometer in the radiator neck may give you a clue to it's accuracy.
Gauge checked out fine (thanks, porknbeaner). Plenty of coolant (thanks). Gotta be the thermostat because I drove home in 95 degree heat and it all worked just the way it was supposed to. Oddly, that includes the thermostat. I am guessing that once the car cooled down it snapped shut. But I'm still going to replace it - it's cheap insurance and I don't trust it anymore. Thanks, everyone!
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