I have a 1998 Lexus LS 400. When I bought it I was told to always use the highest premium gas available which at that time was octane of 91…
Subsequently a couple of knowledgeable oil men told me that its a waste of money…to go down a level and get gasoline with an octane rating of 89. I did and noticed not one speck of difference between the 2 octanes as far as the power of the car was concerned.
Then super premium was lowered to 89 and the next premium level down was 87…so I used 87 and had no problems.
Now super premium is back up to 91…moderate premium is 89 and regular unleaded is 87…so I started using regular unleaded.
My question is…does octane determine the quality of the gasoline alone or is there something else in the different grades of gasoline that is important? Please steer me straight on this issue. Can the use of just regular unleaded gasoline hurt my engine in any way?
Octane level has nothing to do with quality. It is a measure of the gasolines “knock” resistance. Your car will get zero benefit from it unless it was designed specifically to take advantage of it.
Look in your owners manual for what you should use. Anything higher is a waste of money.
Yeah, if you are having problems with knocking, you may be using a gasoline with too low of an octane rating. You are more likely to be having a problem that the high octane is compensating for, such as advanced timing, high intake air temperature, overboosting, or demanding excessively high power at a low RPM.
Berkut is entirely correct. Buying a higher octane than you need is a waste of money.
And I heard (sorry, no cite) that it takes more crude oil to make high-octane gasoline—therefore depleting more resources.
And also, as Berkut said in his/her second post, if your car seems to require a higher octane than the owner’s manual suggests, it’s either got problems that need to be fixed, or someone has modified it for higher performance.
By the way, my sister used to have a '91 LS400. I believe the manual said 91 would deliver the best performance, but 87 was acceptable. She used 87 for several years with no trouble.
This vehicle, like most modern autos, has a “knock sensor” that detects preignition. The car’s computer can retard the timing and avert severe engine wear should a lower octane fuel be used. This is why you have not noticed any major problems running lower octane fuel.
If an auto engine is designed to run best on a higher octane fuel, it most likely has a relatively high compression ratio. The engine will not perform at it’s best when running on low octane fuel.
The cost of premium fuel should weigh heavily in the decision to purchase a “premium vehicle”.