Is Premium gas required or can you use regular gas
Typically, you can switch between premium and regular for different preferences of power, fuel mileage, price, etc. You're Lexus is strongly recommended to use premium. If premium is typically 10 cents higher per gallon and you filled up your entire 19 gallon tank you're only looking at $1.90 extra per fill up. To me, $1.90 per week or so is not worth risking performance now and reliability in the long run. Also, remember that premium burns more efficiently so you're mpg's will be slightly higher... this may come close to balancing out the $2 more you'd spend anyways.
When you put the numbers out there to show the difference to fill up, using Premium gasoline is definitely what I prefer. I believe in treating the vehicle well to extend the life of the vehicle. The less maintenance I have to endure, the happier I will be.
You do realize that Premium is a minimum of 30 cents higher than regular and 15 cents higher than mid-grade. Not sure where the 10 cents came from. Anyway, with the math it's still $5.70 more per fill up. If you are filling up twice a week then you will be spending an extra $10.40 per week which is $42-$53 per month. This may be worth it for you. Yet I find with Toyota products, toggle between mid and premium works just fine.
I am using a unleaded for 7years now on my rx350 is it ok to switch premium at this time after years using of u leaded?
Use of ethanol blended gasoline in a gasoline engine Lexus allows the use of ethanol blended gasoline where the ethanol content is up to 10%. Make sure that the ethanol blended gasoline to be used has a Research Octane Number that follows the above. This is from the owner manual, I guess it does not even said that it should use premium. It just said it can.
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