I have 1997 Corolla CE around 120k miles (4a-fe 1.6L ; 3-speed auto transmission). My car doesn’t have tachometer. My daily commute about 20 mile one-way, including 10 miles on highway which every body drives about 70-80mph (speed limit is 75). I always drive around 70-75 mph to follow the traffic (I can’t push to pass 75mph anyway) but wondering whether I push it too hard on the engine because it has only 3 speed auto without overdrive. I always turn the air condition off the help it. So my questions are: 1) Anyone know how much the engine rev on this 1.6 4A-FE engine? And what is the rev limit? 2) Would it helps if I use 10w-30 dino or synthetic oil instead of 5w-30 (manufacturing recommend) in the summer? I lived in Tennessee which around 100’ in summer and around 30’ in winter. Thanks.