What effect will running 87 octane in a car that recommends high octane have

My daughters both own newer vehicles that recommend using high octane gas, but the dealer has told them the ECU will adjust to run on 87 octane and they could get away with just putting in high octane when they are going to be hauling heavy loads or driving in the mountains. What effect will running 87 octane in them have on performance and mileage. One daughter has a 2006 Toyota Tacoma v6 and the other has a 2010 Acura TSX.

I use 87 in my Lexus ES300, have for 14 years, no problems, it’s ‘recommended’, not ‘required’. I notice no difference in performance or economy. I bet the same is true for the Tacoma, I’m surprised premium is ‘recommended’ for it. As for the TSX, just make sure the manual (not the dealer) says premium is ‘recommended’, not ‘required’.

92 octane is not “high”…It’s a joke. Most engines will tolerate 87 octane without any problems. If you can not detect any “spark knock” or “detonation” with your ear, no engine damage is being done. At one time, Premium Fuel was rated at 100 octane or more. High octane Av Gas was rated at 140 octane…

The 87-92 octane spread fed to consumers today just isn’t enough to worry about. It CERTAINLY isn’t worth .25-30 cents a gallon extra…

The Tacoma does not spec 91 octane, it’ll run fine on 87 octane. The TSX will run on 87 but the recommended octane is 91 or better. It will some amount of power and some amount of fuel mileage, how much it loses varies greatly from model to model. I know that vehicles with Nissan’s VQ V6s tend to lose about 12-15% in power and mileage when 87 octane is used instead of the recommended 91 octane. I’m not sure what the loss is on the TSX though.

If it were me, I would use what the owner’s manual recommends. The cost difference between filling up with premium vs. regular is miniscule in the big picture of the costs of automobile ownership.

It would seem to me that there has to be a reason why they recommend the higher octane. If I am correct the newer engines which recommend using higher octane are just like the older engines that required high octane, except the computer on newer engines dials back the timing and adjusts the air/fuel mixture when it senses engine knock, allowing it to run on regular gas. Where as the older engines didn’t have the advantage of the computer to control things and had to run high test all the time. If this is true it would seem that there has to be a loss in power at the least when the timing is backed out and the gas mileage should decrease as the computer richens the mixture to avoid knock. I also may not have a clue what i’m talking about.

When you drive a car with forced induction and has a custom dyno tune that was written with 93 octane in mind as the baseline fuel. It’s very important to use the proper fuel.

The CAR MAKER recommends, and bases warranty, on using the higher octane fuel. Who should be second guessing the car designers and engineers?
The vehicle engine computer fall-back timing tables are set for the recommended octane. If the knock sensor fails (which they can), and the built-in tables are used, knock can occur. Knock can damage an engine.

Your ear will tell you to do something LONG before any damage occurs…Few people today have ever heard pre-ignition spark knock…Myself and most other Cadillac Allante owners have found their cars run just fine on 87 octane fuel, although every one ever built was labeled “Premium Fuel Only”. Five octane points is just not that big a deal…

Engines have had knock-sensor adjusted timing for a long time. I imagine mine might get a slight hp bump if I use premium, but I haven’t noticed the difference, and the milage is unchanged. Typically the timing is adjusted, but I don’t think the mixture is changed to avoid knock. Like FoDaddy said, different engines vary greatly in their sensitivity to octane. Numerous posters talk about BMWs and their great reduction in performance with regular.

Older drivers understand knock (ping) when they hear it, realize what damage it can do to their engine, and, as a result, ease up on the acceleration. Other drivers, which are MOST drivers, have no idea that a sound might be knock (ping), and have no idea what to do to stop it (lessen the load on the engine). Some won’t even HEAR, or heed, the engine knocking because of various reasons (cell phones, radio, oblivion).

It should not damage their cars, but they are not likely to get the mileage they would with the recommended octane and they likely will not get the power they paid for when they bought their cars.

Many modern cars have sensors that dumb down the cars when they sense lower octane fuel. That will reduce power and mileage. In the old days it would only say use high octane and failure to do so would damage the engine as it will today for an engine that requires (not recommends) high octane.

The owner’s manual may say that premium is required or that it’s recommended. If it’s required, failure to use it could lead to engine damage not covered by the warranty. If it’s recommended, the engine should adjust to the lower octane by changing the timing (assuming the knock sensor never fails), but this could lead to reduced gas mileage, cancelling out any financial benefit.

Yes, that is correct…ASSUMING that everything will continue to operate, perfectly.

My wife has a 2006 Sienna with a 3.3 litre V6. The Owner’s Manual “recommends” premium for better performance. We’ve used regular since new with no driveability issues in the 3.5 years we’ve owned it.

The Premium vs. Regular debate comes up on a continual basis. Out of curiosity I started using premium in the van for a few months and compared the mpg with the previous year (regular). The short version was there was no difference in mpg or performance between premium and regular gas in the Sienna. Here is the thread on the subject. The results should be taken with a grain of salt.


Note, the Sienna is not driven hard, perhaps if the wife or I were more aggressive Premium might make a difference.

Ed B.

At one time, Premium Fuel was rated at 100 octane or more.

Yup - on a different scale . Today’s 93 octane = 98 octane in the old system .

Probably won’t harm the engine…the knock sensor will detect knocking and retard the timing. Retarding the timing will reduce performance and gas mileage…so I really don’t see any savings in using 87 octane.

Lemme get th is straight. Your daughter spent 30+ grand on an Acura, but wants to cheap out on the fuel it uses? 18.5 gallon capacity, at 30 cents more per gallon, that’s still less than $6 extra per fill up for the fuel it needs
From Acura’'s own website:

4-cyl. Premium unleaded 91octane (Recommended)
V-6 Premium unleaded 91octane (Required)
Octane - TSX (I-4)

Customers who choose to use Regular gasoline should expect reductions in power, performance and fuel economy.

Octane - RL, TL, TSX V-6, ZDX, MDX, RDX

Using gasoline with an octane lower than 91 octane may cause damage to the engine. Please consult the owner’s manual for details