Yes, more heat! It's too cold for him to digest right! Also, savs are more insectivores than rodent eaters... Just a heads up, high rodent diets can cause an early death from fatty liver..seen too many people lose their savs to that. I'd get started on some big insect colonies pronto if you want him to live a long life!
In the wild, even adult savs are insectivores!
http://savannahmonitor.org/