In a previous life I was a Service Advisor at a Ford dealership and I saw a few problems stemming from people using regular gas in a motor designed for premium. (Mainly pinging, loss of power and starting issues.) In reference to this...my sister-law drives an '07 Range Rover Sport Supercharged and she refuses to put premium gas in the tank. She thinks premium gas is a marketing ploy set up by greedy gas companies. Let me know if any of you know of SERIOUS problems stemming from her insistence on doing this. I only know what I have seen in Fords and I know they are not tuned like the high performance Rover V-8.
I don't have an range rover... I have a 2006 MINI cooper s and i have to use premium my engine has a fit. It pings and shutters with lower grade gas. What will sux for your sister is when she has major problems with her engine latter down the road, they can possible void all repairs that might have been covered by warrenty if they find out she wasn't using premium in her vehicle. Unfortunitly she might have to learn the hard way and learn from paying an outrageous repair bill that she could have avoided. Of all people she should be listening to you since u've seen problems first hand.
She is leasing the truck...so she says she doesn't care if it damages the engine in the long term. I wonder how many people who lease really do abuse their vehicles like this. I am sure a sizable portion. I did at least tell her that if it starts to ping and stutter over a prolonged period of time that could damage internal engine components. I just wonder if a manufacturer has studied the effect low grade gas has on engine durability.
Actually she SHOULD be ok. I would imagine a car of that quality would have knock sensors built in. As long as she drives it easy and doesn't tow with it, the worst she should see is a loss of performance, from the computer making the necessary adjustments. Having said all that, the maker says premium so she should use that.