What can to much caffine do to your body like 8 cups of coffee a day?

Several things. Can give you indigestion and bowel issues (diarrhea). May make one anxious or jittery or hypervigilant. May disturb your sleep. May precipitate more cardiac events (skipped beats), may make one urinate more often and many other symptoms. Everything in moderaton!
Too much coffee. For most healthy adults, moderate consumption of coffee, 1-3 cups per day, would not be harmful. Regular coffee drinking may provide possible health benefits, including lower risk of type 2 diabetes, gallstones and parkinson’s disease. Caffeine contained in coffee, however, can cause insomnia, nervousness, acid reflux, tremors, palpitations, dehydration and irritability. Moderation is the key.