A friend of mine leased a Lexus RX350, and 6 months and 5k miles later, she just discovered that it requires at least 91 octane gas. Can there be any permanent damage at this point? Will using 91 for the next 2.5 years “fix” any damage? Should she use 93 for a period? Any other recommendations?
TIA!
There might have been some knocking and pinging, but probably not even that – modern cars will detect it and adjust timing automatically.
There shouldn’t be any damage.
Yep. In a modern car it will be fine.
I would recommend switching to the required octane.
My 2019 Mazda MX-5 actually says “premium recommended” rather than “required”. IIRC the manual says it will detect the lower octane fuel and adjust the timing accordingly, like @RitterSport said. The worst that will happen is that I won’t get the horsepower they advertise if I don’t use premium.
Yes and I think fifty Hail Marys will give OP’s friend enough time to pray about what she did.
Thanks everyone!
If you put regular gas in a “premium required” car, the computer will try to adjust the timing but can only do so up to a point. Under excelleration, like getting up to speed on a freeway ramp, it may start knocking and pinging. This is not good for the engine and may cause damage over time. Your car warrantee may be voided if you have an engine issue and you take it to a shop and they see that you have been using regular gas.
You can go to the auto parts store and get a bottle of octane booster and that will fix it for that tank of gas, or just run some of it out and fill back up with the proper gas.
You are not saving any money by running a lower octane fuel in a premium required car, in fact you will probably get shittier gas milage, so go back to the required fuel as soon as possible. And all the grades of fuel are of the same quality, premium is no better than regular, it is just the octane rating that matters. There is nothing else ‘premium’ about premium gas.
Higher octane is for high compression engines, usually performance cars, to prevent pre- detonation. My car wil rattle and ping if I put anything but premum it it, most cars will say so right on the gas cap or door, pretty hard to ignore.
Chances are that theknock sensors will retard the timing or whatever it does to prevent damage, and it’ll just be severely anemic as far as power output is concerned.
High octane gas tends to be a turbocharged engine thing these days; with stratified charge direct injection, even 11.5:1 engines can use 87 octane just fine.
Sometimes a car manufacturer will state a particular model or power configuration only requires regular gas when in fact it clearly requires premium. My 2023 Kia Soul has a naturally aspirated MPI 2.0 liter I-4 and both the gas cap and the owner’s manual state regular unleaded (87 octane) is fine. However, running regular fuel through it causes pinging under acceleration, so I run premium (92 octane) in it exclusively. When I looked up the compression ratio I was unsurprised it knocked: 12.5:1.
What do you consider to be “modern”? My wife drives a 2007 Civic Si that’s only supposed to get premium, but occasionally I forget to fill with premium.
Probably modern enough? Looks like Hondas have had equipment to adjust timing since the early 90s. I think it’s called an Engine Control Unit.
Eh, it depends on the car.
I used to have an old Cadillac that “recommended” 91 or better octane, but “required” 89 or better. The car’s mileage was better on the 91 octane, but the cost per mile was better on the 89 octane.
What was interesting was the Toyota Camry I had at the time. It recommended 89 octane, and its mileage actually went down on 91 octane. So “Premium” gas actually made it run worse.
I’ve never had a car that would actually ping if you put too low of an octane in it. Usually the knock sensor detects the pinging and adjust the timing to prevent it from happening.
I have an old Harley motorcycle though that will ping under hard acceleration if I accidentally put too low of an octane in it. Found that out the hard way once. I ran it down to about half a tank and filled it up with high octane and all was good.
Anything built since the 1990s will have a knock sensor and should adjust to compensate for too low octane. So, not very modern, really.
A lot of cars built before then will have knock sensors too. My mid 1980s Cadillac adjusted well to low octane fuel. Some of the cheaper cars in the 1980s didn’t have them though, or at the vey least the engines weren’t able to adjust very well to prevent pinging.
My 2006 Acura has the same octane recommendation, and I’ve mostly used regular 87 octane with no issue. When I drove it regularly, I could (barely) tell what octane my wife filled with just by drive feel. Instrumentation would show the ignition timing was retarded when running the lower octane, and more advanced with higher octane.
Oil analysis showed no concerns.
Occasionally I’d mix my own octane, filling approximately half the tank with regular, and half the tank with premium (mid-grade is a 60/40mix of regular and premium blended by the pump).
OP, if there is no knocking or pinging, there is no damage and almost any normal modern car (let’s say made within the last 30 years and not a turbosupercharged Porscherarri) will adapt to any fuel you can buy at perhaps some minimal drop in performance.
Premium here costs about 1/3 more than regular. I defy you to find a car that loses a 1/4 of its mileage by running on regular. In every car where I’ve done this experiment, I could not detect any difference in fuel economy whatsoever, and I have done it in three cars where premium was either recommended or required, and one other turbocharged car that only recommended regular. I’m sure my experiments weren’t sensitive enough to pick up a 2% drop in fuel economy, but I for sure would have noticed a 25% drop. Maybe I could feel a slight difference in performance but to be sure, I’d need a dynamometer or a drag strip.
Apparently the rare exception to the “normal modern cars can adapt to any fuel” guideline. While I fully believe you, I still find it surprising.
And if you do the math, this almost always works out to make it cheaper.
I had a 1990 (I think?) Suzuki Sidekick. When it got older and had more miles, it started pinging with regular gas, so I switched it to higher octane. It still had a carburetor. I guess it needed a tune-up or something to get it working well with the recommended regular gas again.
My thought would be what you have is not an engine that needs premium, but rather an engine that needs its knock sensor replaced or recalibrated.