good day guys and gals. just want to ask your comments because i am already using Mobil 1 synthetic engine oil on my 97 Rav and my brother suggested that if ever the oil level goes down i could use a normal engine oil instead of buying another gallon of synthetic oil, there is no available small size of syn engine oil here so he just opted for the cheaper one, mobil plus.. he said that a mechanic friend of him sggested that idea. he has been doing it for quite sometime now and as of the moment i cannot see an obvious side effect. any violent comment on that? anyone tried it before? just curious...