NTC Thermister Resistance Drift?

[The3DE]

I had used a 10k ntc thermister for measure the temperature of hot water (~50-70C) for extended periods of time (~30min), leaving the thermister in the water. Now, a few months later, the thermister has a resistance of ~18k at room temperature. I checked another unused thermister from the same batch and it still had a normal resistance of 10k at room temperature. The thermister still works; when I heat it up, the resistance still drops. Is the thermister still usable? Normally it is used in a voltage divider with a 10k resistor but if I changed it to a 18k resistor, would it still work/ be accurate? Also, why would the resistance of it change?

Thanks

[Cliff Matthews]

Is this part resistant to water ingress?

[The3DE]

I'm not sure but it's an extremely cheap part from Ebay. Just a black blob with 2 leads. I tested it more and it seems to have a resistance of about 20k at 25C. There is rust on one lead though. It was delivering pretty accurate values when it was in use. I'm was using it with a micro controller (Arduino) to calculate the temperature using the Steinhart and Hart Equation, but now that somethings changed, idk if it still works with the same beta coefficient. I don't really need the part; I have extras and don't have that much use for them right now. I'm just curious about why it changed and the reliability of this type of thermistor. Also, the thermistor hasn't been in use for a couple months, just to clarify. I only used it for a few days a while back.

[Gyro]

Unless the water was distilled or de-ionized or the leads completely waterproofed, you would have had electrolysis happening between the leads (and connections?). That would have changed the apparent resistance in the water.

If water vapour made it into the thermistor package, then the same thing would have been happening internally, possibly causing a permanent change in characteristics.