Na'urar Thermostat wani nau'in na'urar sarrafa zafin jiki ne ta atomatik, wanda yawanci ke ɗauke da kayan aikin auna zafin jiki, ta hanyar faɗaɗawa ko raguwa don kunna da kashe kwararar ruwan sanyaya, wato, daidaita ruwan ta atomatik zuwa cikin na'urar radiator bisa ga zafin ruwan sanyaya, canza kewayon zagayawa na ruwan sanyaya, don daidaita ƙarfin watsa zafi na tsarin sanyaya.
Babban ma'aunin zafi na injin shine ma'aunin zafi na kakin zuma, wanda paraffin ke sarrafawa ta hanyar ƙa'idar faɗaɗa zafi da kuma matsewar sanyi don sarrafa zagayawar sanyaya. Lokacin da zafin jiki na sanyaya ya yi ƙasa da ƙimar da aka ƙayyade, paraffin mai kyau a cikin jikin na'urar auna zafin jiki yana da ƙarfi, bawul ɗin zafi na thermostat a ƙarƙashin aikin bazara don rufe tashar tsakanin injin da radiator, mai sanyaya ta cikin famfon ruwa don komawa injin, ƙaramin zagaye na injin. Lokacin da zafin jiki na mai sanyaya ya kai ƙimar da aka ƙayyade, paraffin ya fara narkewa kuma a hankali ya zama ruwa, kuma ƙarar tana ƙaruwa kuma tana danna bututun roba don sa ya ragu. A lokaci guda, bututun roba yana raguwa kuma yana tura sama akan sandar turawa. Sandar turawa tana da matsi ƙasa akan bawul don buɗe bawul ɗin. A wannan lokacin, mai sanyaya yana gudana ta cikin radiator da bawul ɗin thermostat, sannan yana kwarara zuwa injin ta cikin famfon ruwa don yawo mai yawa. Yawancin ma'aunin zafi yana cikin bututun fitar ruwa na kan silinda, wanda ke da fa'idar tsari mai sauƙi kuma mai sauƙin fitar da kumfa a cikin tsarin sanyaya; Rashin kyawunsa shine cewa thermostat yakan buɗe kuma yana rufewa lokacin aiki, yana haifar da yanayin juyawa.
Idan zafin aikin injin ya yi ƙasa (ƙasa da 70°C), na'urar auna zafin jiki tana rufe hanyar da ke kaiwa ga na'urar auna zafin jiki ta atomatik, sannan ta buɗe hanyar da ke kaiwa ga na'urar auna zafin jiki ta ruwa. Ruwan sanyaya da ke fitowa daga na'urar auna zafin jiki yana shiga famfon ruwa kai tsaye ta bututun ruwa, kuma famfon ruwa yana aika shi zuwa na'urar auna zafin jiki ta ruwa don zagayawa. Saboda ruwan sanyaya ba ya wargajewa ta na'urar auna zafin jiki ta ruwa, ana iya ƙara zafin aikin injin cikin sauri. Lokacin da zafin aikin injin ya yi yawa (sama da 80°C), na'urar auna zafin jiki tana rufe hanyar da ke kaiwa ga famfon ruwa ta atomatik, kuma tana buɗe hanyar da ke kaiwa ga na'urar auna zafin jiki. Ruwan sanyaya da ke fitowa daga na'urar auna zafin jiki ana sanyaya shi ta na'urar auna zafin jiki sannan a aika shi zuwa na'urar auna zafin jiki ta na'urar auna zafin jiki, wanda ke inganta ƙarfin sanyaya kuma yana hana injin yin zafi sosai. Ana kiran wannan hanyar zagayawa da babban zagayawa. Lokacin da zafin aikin injin yake tsakanin 70°C da 80°C, manyan da ƙananan zagayawa suna wanzuwa a lokaci guda, wato, wani ɓangare na ruwan sanyaya don babban zagayawa, da kuma wani ɓangaren ruwan sanyaya don ƙaramin zagayawa.
Aikin na'urar auna zafin jiki ta mota shine rufe motar kafin zafin jiki bai kai ga yanayin zafin da aka saba ba. A wannan lokacin, ana mayar da ruwan sanyaya na injin zuwa injin ta hanyar famfon ruwa, kuma ana gudanar da ƙaramin zagayawar da ke cikin injin don sa injin ya yi zafi da sauri. Idan zafin ya wuce na yau da kullun, za a iya buɗe ruwan sanyaya ta cikin madaurin radiator na tanki don yaɗawa sosai, don haka zai yi zafi da sauri.
