I was reading an article about how to slightly increase your gas mileage. One thing that it said was to make sure you use the proper oil for your engine. The '90 Celica I have is recommended to use 5W-30 oil but since I have had it, I have always filled it with 10W-30. I remember having other vehicles in the past where 5W-30 was recommended but 10W-30 was used.
Should I be using 5W-30 and not 10W-30? If I switched to the "correct" oil, is it possible that I would notice some slight improvement?
Thanks!