I own a '00 Lexus GS300 and it says Premium fuel only on the gas cap. Would it be harmful to use reg. unleade

it will run like crap but yes you can use it.you will here valve rattle, run on after you shut it off.piss poor gas mileage.

no it would not be harmful, but the performance would be less than amazing. personally, l cannot see the difference in the performance (i drive an 05 es330). l used to use premium but l switched because of the prices and notice no difference but the computer in your vehicle is designed to process any type of fuel, just not diesel.

no it would be ok .. but what u need to know is which one gets u the best miles it will vary between brands & types of gas even depends on where u live & how one drives.. so what u do is buy a tank at the place u find easy to shop at. fill up & mark down the miles burn out that tank mark the miles try another octane do the same mark down the miles then subtract to see which one got u down the road more & that one is the one u want. dont matter if it was high or not if u dont get better mileage then its costing u money

Yes, it is bad to use regular. That is why it says premium on gas cap.

Regular gas would make engine knocking sounds.