Ray,
It seems to me that most newer cars recommend 91 octane fuel. I think it is mainly because high octane fuel increases fuel mileage slightly. But high octane fuel costs a lot more than the small increase in mileage. I think that as long as an engine does not make strange sounds with regular octane fuel it is not doing any harm to the engine. Please let me know what you think.
Clark
You are incorrect. (I am not Ray, BTW) The octane in itself does not increase MPG’s. Only if the engine is tuned to make use of the higher octane, does the MPG increase.
You are wrong there, too. Detonation or pre-ignition can exist such that you cannot hear it and there for cause some damage to the engine.
As we tell posters here that want to justify putting 87 octane fuel in cars that REQUIRE 91 or 93 octane fuel; Don’t do that, use the fuel required by the manufacturer. If it says 91 octane preferred, then the car is configured to run best on 91 but you can use 87. If the manufacturer say 91 is REQUIRED, use that or damage may occur.
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How do I know that you are someone that knows what they are talking about or just someone that has an opinion?
Ray doesn’t ever respond here as far as I know. I can vouch for Mr. Mustang as someone who does know what he is talking about. You are welcome to your ideas but you are a little off base. Most vehicles sold are designed to use regular unleaded 87 fuel . But if it requires premium then that is what should be done.
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Do you think Toyota does not know what they are talking about either?
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You don’t.
But you posted on the CarTalk Forum looking for answers, I obliged and reiterated what every owners manual says about fuel octane. I just answered your “I think” theories. If you don’t believe my answer, fine, do your own research. It might be fun.
I’d suggest reading “Internal Combustion Engines and Air Pollution” by Edward F. Obert for starters.
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I like the topic. I disagree that “Most new cars recommend 91 octane.” My estimation would be that maybe 20% of the cars sold in America come with this recommendation. Not a single top selling car model in the U.S. has that recommendation that I know of. Rogue, CR-V, RAV4, Camry, Accord, Civic, Corolla, Altima, Sentra, Model 3, that is pretty much the list of top sellers accounting for a massive part of the market. Throw in the F-150 if you like. None suggest or hint at 91 octane that I am aware of. There are premium and luxury models that do recommend the pricey stuff, and I think the reasons are 1) Bragging rights for a handful of HP 2) Fuel economy as you suggest.
That is incorrect.
That is also incorrect.
I think that you need to do a considerable amount of research on this topic, rather than relying on your assumptions.
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On page 474 of the 2017 4Runner owner’s manual, Toyota says to use 87 octane or higher (91 research octane). Note that there are two numbers. Research octane (RON) is used in Europe, while the Anti-knock index (AKI) is used in the US and Canada. There is a third index called Motor Octane Number (MON). AKI is the average of RON and MON. If you are in North America, use 87 AKI. If in Europe, use RON. Given the information in the owner’s manual, you can calculate the MON if you want to.
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@ClarkTuck , you came here asking for an opinion and unfortunately for you making a statement about mileage that is incorrect. Then you have the audacity to challenge one of our respected members when they give you solid, expert, free advice. You might want to sit back a bit and see what the other replies are and you will see that @Mustangman was right on with his answer.
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This is what the owners manual states about using 87 octane fuel;
You may occasionally notice light knocking for a short time while accelerating
or driving uphill. This is normal and there is no need for concern.
I wouldn’t be concerned with octane with modern vehicles, they all have knock sensors that are necessary to control the oxides of nitrogen that might exceed federal standards if pre-ignition were allowed to occur.
Some do, some don’t. Vehicles with normal aspiration (and some with turbos)with direct injection and/or both direct and port injection typically can be run on regular unleaded. The 2017 Toyota 4 Runner will run on regular unleaded (it has standard port fuel injection), there’s no benefit to using premium.
Only when the engine has been designed/tuned to take advantage of premium fuel. Otherwise there’s no real difference in fuel economy.
Depends. On vehicles that recommend premium, but require regular, there will be a difference in both fuel economy and power. A good example of this the Ecboost 4 cylinder Ford uses in the Mustang.When it came out it was rated for 310 HP when running on 93 octane. On 87 octane it’s output fell to around 275 HP. Which is noticeable. Fuel economy also drops, for some cars you’re still money ahead using regular, on some others, it’s a wash or a slight money-losing proposition.
You’re best off using the recommended fuel as stated by the manufacturer. You should always use at least the required fuel. Recommended and Required are not the same thing. If your owner’s manual recommends premium you can likely get away with using regular without ill-effect other than reduced power and fuel economy. If premium fuel is required then that’s what you should use. Using lesser fuel can potentially lead to problems (holes in pistons for example).
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On internet forums like this or any other there’s no way to know. Any post here could be a 13 year old kid waiting at a bus stop w/nothing to do until the bus arrives. If you need to be sure you are getting an expert’s advice, the place to obtain that is at the dealership or your local well-recommended auto repair shop. Bring your wallet. It is possible to assess what a poster has said on prior threads by clicking on their handle, so that’s one method to make your own appraisal of the merits of their comments.