you are using mobil 1 and that is the very best oil you can use, i believe. BUT it is also aboutt he most expensive so now you have a trade off.
I believe in changing the oil, often, 2000-3000 miles interval. All major oils have to meet the SAE specs (SG, SH, SI, whatever-letter-it-is-up-to this week). So its my belief that it doesnt matter so much WHAt brand you use, its much more important how often you change it. I use mostly havoline and penzoil, sometimes castrol. The engine seems not to like quaker state or valvoline (tick tick tick sound) so i dont use those much.
There is dirt and water in the oil and the longer you leave it in the worse it gets, of course. The filter can only do so much cleaning of the oil, this $3 can of paper is not going to perform any oil cleaning miracles so the only sure way to keep the engine in good shape is change the oil.
Mobil 1 is the very best out there - a dino oil has additives that begin to wear out in just a few hundred miles. And after a few thousand they are pretty much gone. With mobil 1 the additives last much longer, but even this oil can do nothing about dirt and water in the oil. My suggested interval to you, your Mobil 1 = change oil and filter at 5,000 miles. If you go back to dino (and i have gone back and forth from dino to synthetic and back again, many times, on many cars, and have never noticed any ill effects) - 2,000 to 3,000 miles.
BTW i have a 2002 Camry with 90,000 and an 1988 nissan pickup with 300,000 miles that runs like new and passes smog. I change their oil often, of course.
Most name brand oils will suffice for 5000 miles be it dino or synthetic. The 3000 miles thing is is from the oil companies trying to milk more of your money. Do you think that Toyota engineers would suggest 5000 mile or 7500 mile oil change intervals without doing some research?
they do it for sales reasons, what if you know nothing about cars and are shopping for a car or maybe even a fleet of cars, and toyota is the only one that says change the oil at 3,000? If youre a fleet manager all you see is $$$ out the window.
Moreover if you read the fine print on many if not most automakers owners manuals - they usually state "For severe service driving conditions, change the oil at 3,000 miles". So big deal, who drives severe service anyway? Ans: EVERYONE!
Toyota makes a fine product, about the best or we wouldnt have bought one. But their goals are different from ours! Their goal: Sell cars, stay in business. OUR GOAL: Make this bucket last for a gazillion miles so i dont have to spend another $15 or 20 grand anytime soon!