Saboda ƙayyadaddun ƙarfin zafi na ruwa yana da girma, haɓakar zafin jiki bayan shayar da zafin silinda ba shi da yawa, don haka zafin injin ta hanyar da'irar ruwa mai sanyaya ruwa, amfani da ruwa azaman jigilar zafi mai ɗaukar zafi, sa'an nan kuma ta hanyar babban yanki na dumama zafi a cikin hanyar zubar da zafi na convection, don kiyaye yanayin aiki da ya dace na injin janareta na dizal.
Lokacin da zafin ruwa na injin janareta na dizal ya yi yawa, famfo na ruwa yana bugun ruwa akai-akai don rage zafin injin, (Tunkin ruwan yana kunshe da bututun jan ƙarfe mai zurfi. Ruwan zafin jiki yana shiga cikin tankin ruwa ta hanyar sanyaya iska da kewayawa zuwa bangon injin silinda) don kare injin, idan yanayin ruwan sanyi ya yi ƙasa sosai, wannan lokacin zai dakatar da kewayawar ruwa, don guje wa ƙarancin zafin injin dizal.
Tankin ruwa na dizal yana taka muhimmiyar rawa a jikin janareta gabaɗaya, idan aka yi amfani da tankin ruwa ba daidai ba, zai haifar da lalacewa ga injin dizal da janareta, kuma hakan zai haifar da gogewar injin dizal a lokuta masu tsanani, saboda haka, masu amfani dole ne su koyi daidai amfani da injin ɗin dizal saita tankin ruwa daidai.