Does a food thermometer needs tevila?
Essentially you do not have to tovel it, however it would be preferable to tovel it without a bracha. The reason for this is, since it does not actually prepare the food, and it is also not used to eat the food, it doesn’t need tevila. Nevertheless there are poskim that say to tovel it without a bracha. It should be noted, that although normally when toveling an electronic device the whole device (handle etc.) should be immersed in the water, since the thermometer essentially doesn’t need tevila, you can tovel only the metal part that comes in contact with the food, and not the handle.
Chut Shani Tevilas Keilim pg. 22, Chayei Halevi 5-66 (9), Ohel Yackov (R. Y. Skoczlas) Tevils Keilim ftnt. 272 brings that this is the opinion of R’ S. Doblitsky zt”l, and Ybchl”ch R’ E Shlesinger, R S. Gross shlit”a, that it does not need tevila. This is also the opinion of Rav Y. Cahen shlit”a. On the other hand, Ohel Yackov brings in the name of R’ C. Kanievsky , R’ E. Auerach and R’ M. Deutsch shlit”a to tovel it without a bracha.