Saboda takamaiman ƙarfin zafi na ruwa yana da girma, ƙaruwar zafin jiki bayan shan zafin silinda ba ta da yawa, don haka zafin injin ta hanyar da'irar ruwan sanyaya, amfani da ruwa a matsayin hanyar isar da zafi, sannan ta cikin babban yankin wurin nutsewar zafi ta hanyar watsar da zafi mai convection, don kiyaye yanayin aiki mai dacewa na injin janareta dizal.
Idan zafin ruwan injin janareta dizal ya yi yawa, famfon ruwa yana tura ruwan akai-akai don rage zafin injin, (Tankin ruwa ya ƙunshi bututun jan ƙarfe mai rami. Ruwan zafi mai yawa yana shiga cikin tankin ruwa ta hanyar sanyaya iska da zagayawa zuwa bangon silinda na injin) don kare injin, idan zafin ruwan hunturu ya yi ƙasa sosai, wannan lokacin zai dakatar da zagayawa ruwa, don guje wa zafin injin janareta dizal ya yi ƙasa sosai.
Tankin ruwa na janareta dizal yana taka muhimmiyar rawa a jikin janareta gaba daya, idan aka yi amfani da tankin ruwa ba daidai ba, zai haifar da lalacewa ga injin dizal da janareta, kuma zai kuma sa a lalata injin dizal a cikin mawuyacin hali, saboda haka, masu amfani dole ne su koyi yadda ake amfani da tankin ruwa na janareta dizal daidai.
