Does anyone know what type of sensor this is? It reads 12.5 ohms and has two pins. I belive that white stuff is thermal compound
I would guess it is temperature sensor, not sure just guessing. Try warming it up and measure the resistance.
I would guess temp sensor also and suggest the same. Measure resistance at ambient and warm the probe part up and look for change. The 12.5 ohms is a little peculiar.
Platinum resistance element I suspect. 100 ohms is common, but 25 isn't that rare, 12.5 seems plausible
as a not-very standard value (perhaps you put several in series in some applications to measure average
Looks like an automotive temperature sensor designed to go in a well immersed in fluid (oil, water). The white stuff looks like heat conductive paste, and the connector suggests automotive.
Most Negative Temperature Coefficient (NTC) types are defined as resistance at 25°C, RTD sensors (Positive Temperature Coefficient types) are based on resistance at 0°C so base resistance of 100 ohms at 0°C is an RTD100, RTD1000 would be 1000Ω at 0°, so it isn't one of them.
Quick test is put it in the freezer (usually about -20°, or iced water at 0°, and measure resistance, then boiling water and measure again, then at least you know which way the curve goes before determining what type it is.
Likely as not it'll have a specialist curve for the intended application, where the flat part of the curve is optimised for the range of interest, so of limited use elsewhere.