Gasoline Octane Required

Will the following run on 87 octane?

2007 Acura TL 3.5L V6

2007 Lexus IS 250 3.5 L V6

2005 Cadillac STS V6

Yes, but doing so will cause long-term damage to their engines. Vehicles that specify 91-octane gasoline NEED the octane to operate correctly. Using regular gas in these vehicles will not save money in the long run, because the repairs will far outweigh any savings at the pump.

The knock sensors will mask the noise, but the damage will continue to occur.

Worst case scenario: holes in the pistons.

Worst case scenario: holes in the pistons

damaged block(top of the cylinder walls), deformed squish area of the head also sounds good.

I’m not sure I’d say “sounds good,” but, yes, those are also likely to result from insufficient octane. This is not how you save money.


I can afford the car $10k+ premium for the marque but not the extra $10/month for fuel assuming (15k miles/year & 25MPG).

Most “Premium Only” engines will run fine on regular. Four octane points is simply not enough to worry about and .22 cents a gallon is too much to pay for four octane points. If you can not detect any detonation or spark knock, no damage is being done to the engine.

Back in the Good Old Days, regular was 89 octane and most premium was 100 octane or better. That’s 11 octane points and that does make a considerable difference. The 10.5 to 1 compression “performance” engines of that period did indeed require premium fuel. Check the compression ratios of the engines you are considering and compare them to “regular fuel” engines. Most 9.6 to 1 compression engines will run on 87 octane without any problems…In many cases, the “Premium Fuel Only” label is a gift to the oil companies. A more honest label is “Premium Fuel Recommended” which means it will run fine on regular…

But as I said, damaging pre-ignition is VERY noticeable, you can’t miss it, so if you can’t detect any funny rattling sound, especially during acceleration, you need not worry about octane.

If premium fuel is only “recommended”, you should be able to get by with regular. E-10, which has a higher octane rating because of the ethanol, would be better. It might also be cheaper than straight regular. If premium is absolutely required, you should not run anything else. For the final word, check with dealers or the manufacturers.

Even if you can get by with less than premium, I have read reports that engine efficiency decreases with lower octane fuel. The result is higher fuel consumption which cancels your savings.

As others have said, if you can afford to buy the car, you can afford to buy premium fuel for it. Use regular only if you are out of gas and premium isn’t available.

Use of regular gasoline reduces performance and lowers fuel economy, but it won’t damage the engine because of the knock sensors.

The knock sensors often run in closed loop fashion with the computer and ignition: the ignition continually advances in stepwise fashion until the knock sensors detect the start of engine knocking (still below the threshold of human hearing). The ignition backs off a step, waits a moment, and then tries to advance again, repeating the cycle. In this way the ignition advance is always set just below the onset of knocking.

One could observe the mpg using premium versus regular and compare that to the difference in gasoline prices. You may find that it’s cheaper to use premium.

Check the owner’s manual. If it say it “needs” high octane, then it needs it or you may suffer engine damage, will suffer a power loss (why would you buy a powerful car and not want power?) and you may not save anything since you will also loose some mileage. (how much will vary greatly with different cars and driving habits.

If it recommends it, but indicated that regular may be used, that means the engine will recognize the lower octane and adjust, protecting the engine, but costing you power and mileage.

I believe all three have knock sensors and will retard the timing to compensate for the lower octane gas. This means you can use 87 octane occasionally when higher octane is unavailable.

However, running the engine with low octane all the time will cause it to run hotter and can have an effect on long-term reliability. Stick with the recommended octane whenever possible.


Most if not all cars produced since the 1990s use knock sensors, a device that detects sound. The knock sensor or sensors (some cars have two), are attached to the engine block can hear knock or detonation.

You can safely use 87 octane fuel if your owner’s manual says premium is recommended. If it says, premium must be used, then you must use premium. If it says premium must be used for best results, then you can use regular. You get the idea about the wording.

Google Lewis Gibbs Knock Sensor and Gottfried Schiller Car and Driver for more on this topic.

None of the above. You can use 87 octane, but because these vehicles use a V6 engine they would benefit more power if you use a mid-grade (89 octane). Here’s why:

A V6 engine has more compression than a 4 cyliner engine. If you use regular (87 octane) all the time you risk burning a lot of fuel when driving in-town city; with prolonged use, your engine could ping & rattle, causing mechanical performance & fuel economy issues even though the owner’s manual recommends that octane. Both my 1989 Toyota Camry & 2008 Toyota Highlander have a V6 engine for better power when driving. When it comes to in-town city driving I use mid-grade fuel; 100% highway driving without traffic (e.g. long distance vacations) will benefit better mileage if you use 91 octane because it burns very lean.

A V6 engine has more compression than a 4 cyliner engine.

That is a generalization that need not be always true. While I would guess most V6’s will have higher compression than most 4 cylinders it only takes that one exception for the reader to end up with a hole in his piston. Sure many cars have knock sensors, but they are not all designed to handle the amount of knock that regular may cause. In this case it is far better to follow the advice in the owner’s manual and noting the difference between must use and recommended.

It has nothing to do with the number of cylinders or how they’re configured (straight, V, horizontally opposed (boxer), or even W. It’s simply a function of the compression.

Regular detonates more readily that premium.

If your engine is high compression (many new engines use supplementary compressors to boost compression, some are sctually higher compression via the mechanical ratio in the chamber) than premium will be required because the heat created when the fuel is compressed may actually trigger ignition before the spark plug does. If you use regular in these cases it can cause engine damage. In these engines premium will be “required”. If ignition is initiated (by the heat of compressing the fuel) before the spark fires, the knock sensor system that senses the shock wave and retards the spark will not help.

If your engine is only modestly higher compression, it may be just high enough to trigger a secondary ignition after the spark plug fires when the wave front propogates in the chamber, causing pinging. Longterm pinging causes internal damage. In these cases, your engine may be able to compensate by retarding the spark a bit. It senses the shock from the wavefronts clashing (with a “knock sensor”) and retards the spark. In these engines you may be able to run lower octane without damage, but your performance and mileage will suffer. In these cases premium may be “recommended” but not “required”.

In regular compression engines, regular fuel can be used without preignition, because the heat created from the compression doesn’t get too high and the combustion is fully controlled by the spark. Preignition is not a problem.

If you want a vehicle that runs on regular, simply buy a vehicle thats designed to run on regular. There are lots of great choices.

not to raise such a question… BUT;

how can there be SO many different thoughts about this? (other than check the manual)

is this a case of “OLD” technology being replaced (or better yet, modernized) to catch up with new tech?

OR… are these “old wives tales” being debunked?

are some people just not realizing the changes in new engines, and the squeeze of power output per pound?

Excellent question Cappy. I think the reason there are so many thughts on the subject is that some folks don’t fully understand WHY some cars require premium while some only recommend premium and some run fine on regular. There’s a perception that “premium” is just a rip off, or that the only real difference is the detergents. And then there are some “old wive’s tales” floating around. Many folks also believe the only difference is in the performance of the car.

I usually try to explain the reason, but I’m sure many don’t understand what I’m saying.

Yeah, I’d agree that the new technology has complicated the matter. In the old days, days of 165 degree thermostats, lower compression ratios, rich running carbs, and no turbocharged (and now spercharged) engines except on hot rods, the regular stock cars all pretty much ran on regular. Only performance cars needed premium. But now the engines run hotter and leaner and compression boost is being used on family cars. So it’s become more of a problem.

Abd most people only choose to believe their owner’s manual if what it requires doesn’t cost money.

If you can’t afford the gasoline, you can’t afford the car. You really won’t like paying for the scheduled maintenance or the repairs because you skipped the scheduled maintenance. Pour the good gas into it.

You can use the low (87 grade) octane on these vehicles, but the fuel will burn too quickly if you use it all the time. For better power & fuel efficiency, use the mid (89 grade) octane on a V6 engine. However you may alternate between both octanes of fuel.