I was just wondering about this issue this morning. Your info is good to know.. I've been driving an HS Hybrid for 5 years and having a conventional engine is going to take some getting used to gas mileage/cost wise. If it needs premium so be it, but I'll try the regular.We have a goofy kind of summer fuel here in California.Very volatile. Thanks for posting this.

 

I believe that the key is whether the engine knocks. If it doesn't knock, the engine ECU is doing its job keeping the timing and mixtures in check. So if it doesn't knock or create any error codes, running it on regular should be just fine. I've talked to my Lexus service adviser about this and oil type just to make sure. He said that premium is a suggestion (not a requirement/recommendation) and that regular oil is just fine (versus synthetic). Obviously, synthetic is a better performing oil but if it really doesn't make any difference in the life or performance of the engine for regular (versus racing) use, then his opinion was that there was no need to spend the extra money on the synthetic. So I use regular gas and oil but change out the oil religiously at a maximum of 3k miles. (Sometimes I do use the Firestone blended oil when they have an oil change on sale for $20.)

 

That all sounds reasonable enough. Thanks.