Premium vs. Regular: Addition to the FAQ:


#1

Hi,

I have a 2005 Acura TL. The vehicle instruction booklet states that 91 octane is “required” for my engine, but my engine is equipped with a knock sensor.

I asked my dealer a while back if using 87 will “damage” my engine, and their response was that it will not damage the engine, but it will build up carbon deposits faster. I assumed this was because 93 had more detergents than 87. So I decided to stick with 93.

But then I came across this article:
http://www.nbcactionnews.com/dpp/money/consumer/how-much-detergent-additive-does-your-gasoline-have

The article demonstrates evidence that Mobil 87 uses as many detergents as Mobil 93. So I drove on 87 for 400 miles (I got the tank as empty as possible before filling it each time). I didn’t experience any audible pinging or knocking, and my gas mileage was unchanged.

I went back to my dealer and presented the above article to them, and asked for a comment. Their response was that 87 would lead to more carbon build up, not because of fewer detergents, but the way that 87 “burns differently in the engine.”

So I recommend adding the following question to your website FAQ, along with an answer: Will 87 lead to more carbon build up, not because of fewer detergents, but the way that 87 “burns differently in the engine”?

For those individuals who respond, please have citations or mechanical/chemical explanations to backup your claims. I’d really like to get to the bottom of this. Thank you.


#2

Acura is designed by engineers. If your owners manual says that 91 octane is required then you should use 91 octane. Using 87 octane saves a little money but you are putting your engine at risk. The best knock sensor in the world cannot protect your engine from burning holes in the pistons. Keep using 87 octane and report back to us in a few weeks. Tell us all how much damage you did and what it will cost to fix it.


#3

I venture to say that both the article you mentioned and your dealer’s conversation are irrelevant to your chief concern, and they are both leading you in the wrong direction.

The manufacturer’s recommendation to use premium fuel is based on octane rating, not on quantities of detergents. The manufacturer is concerned with performance and driveability issues such as horsepower and mpg, not with carbon buildup. There ought to be sufficient detergents in every level of rated major-brand fuel to keep your fuel injectors and engine clean enough.

Your choice of fuel ought to be based strictly on octane rating. Ignore the dealer’s notions about carbon buildup and reports of detergent quantities.

In short, go back to Square 1. Don’t overthink this matter. If the engineers say that 91 octane gasoline is required, then use 91 octane gasoline.


#4

Your logic is, indeed, rusty.

What part of the word “required” don’t you understand? If you wanted a car that runs on 87 octane you should have bought a Honda, not an Acura.

This is one of the reasons I won’t buy a used “luxury” brand automobile. You can’t trust that the cheapskate previous owner(s) used the correct fuel.

Why do people buy luxury cars and then cheap out on the gas? I just don’t get it.


#5

I assume you want to switch to 87 octane to “save money”. You need to make sure it’s really saving you money - as it might be costing you more.

The knock sensor will retard the timing to account for the lower octane fuel. That retarded timing will give you decreased performance and fuel economy. How much of a decrease depends on the vehicle - some more than others.

87 octane fuel typically costs 5% less than 91 octane ($3.80 vs $4.00).
If using 87 octane (vs the required 91 octane) drops your mileage by more than 5%, then it’s costing you more to fill up with 87 octane.

If your car gets 20 mpg, 5% is only 1 mpg. It doesn’t take much timing retarding to produce a drop like that.

You may want to run some experiments to make sure it’s not costing you more to use 87 octane.


#6

“I drove on 87 for 400 miles (I got the tank as empty as possible before filling it each time). I didn’t experience any audible pinging or knocking, and >>>>my gas mileage was unchanged<<<<.”


#7

I think its perfectly reasonable to want to have the choice to switch to 87 if the only sacrifice is a few horsepower. If my engine won’t be damaged, and it won’t get any additional carbon buildup, and fuel economy remains the same (which I have confirmed), then…why not switch to 87?

The manufacturer says 91 is “required” but that the engine will run on 87. Is it wrong to ask why 91 is required, and what they mean by “required”? Does this imply engine damage or additional carbon build up, and if so, why? Is it due to detergents, or the way the fuel “burns” in the engine?

There is never anything wrong with questioning a statement to get more information, and to make your own informed decision.


#8

Just to give you the numbers, on average (both city and highway driving), my car gets 29 MPG on 93 and on 87. For both I tested several hundred miles.


#9

Rusty, I think the carbon build up is a scam. It will help the dealer sell their decabonization service. Still “required” is required if that’s the wording of your manual. Why? That’s an engineering question for Acura.

I’d say regular won’t harm your motor, IF the knock sensor is functioning and you don’t put heavy loads on the motor. If the knock sensor fails, or you experience operating conditions outside the norm where your knock sensor can’t adjust the timing enough motor damage could result. Damage if it occured would be stuff like holes in pistons that would cost multi-thousands of dollars to repair. Todays engines use materials that are light weight and in fact not as strong and durable as engines of the good ol days. That’s why one episode of overheating can warp aluminum heads. Pistons are part of this group. They are light weight and really can’t take much abuse before they are damaged.

In the end it is your choice, your car and your money.


#10

Rustylogic:
Reading your replies makes me ask “why did you post your question in the first place?”

The numerous cautious replies given to you were based both on an understanding for how the engine spark feedback systems are designed and work, as well as how they behave in real life. Not only are you discounting that input, but your replies have a righteous arrogance to them.

There is never anything wrong with questioning a statement to get more
information, and to make your own informed decision.

You didn’t listen to any of the information you received. And worse, you based your decision on a very uncontrolled experiment.

Here’s another look at it. Suppose your vehicle were newer, still under warranty, and you used 87 octane. If your knock sensor went bad resulting in engine damage, do you think Acura would repair it under warranty? They would void your warranty in a heartbeat.


#11

and my gas mileage was unchanged."

Yes, we saw that. We don’t believe it, and we certainly don’t believe this was done under scientific testing procedures. Did you drive exactly the same way, over exactly the same roads, in exactly the same weather on both 91 and 87? If not, then your gas mileage not changing isn’t surprising. Did you go by the mpg calculator in the MFD? It isn’t accurate.

The manufacturer says 91 is “required” but that the engine will run on 87.

Well, actually, I have the same car you do, so I know what the manual says. It says you can run on regular temporarily if premium is not available, but that you should not do it any longer than you have to or engine damage may result.

What you’re doing is looking for an excuse to be cheap and save $2 per fillup on a $35,000 car. You bought a premium car, and now you don’t want to spend the money such cars require. And you’re looking for validation for that excuse from us.

We’re not going to give it to you. If you run on 87, you might be fine. You might not. We don’t know because every engine is different (mine pings slightly on 91 if I get on it at sea level going up hill, and is really only happy with 93 when I can find it). If you’re unlucky enough that your gas experiment damages your engine, Acura certainly isn’t going to help you out with the engine work when they find out you cheaped out on the gas even though they told you not to.


#12

You’re wasting money if you use 93. Mix half 87 and half 93. I’ve been running 89 or 90 octane in my car for many years without an issue (it says to put in 91.)


#13

I think its perfectly reasonable to want to have the choice to switch to 87 if the only sacrifice is a few horsepower. If my engine won’t be damaged, and it won’t get any additional carbon buildup, and fuel economy remains the same (which I have confirmed), then…why not switch to 87?

Knock sensors have been known to fail. If it does fail then you run the risk of severe engine damage. You want the option of NOT running hi-octane…You have that option…buy a car that requires 87 octane.


#14

‘There is never anything wrong with questioning a statement to get more information, and to make your own informed decision.’

IF you ask the correct questions and have the expertise to understand the answer .


#15

You’re wasting money if you use 93. Mix half 87 and half 93. I’ve been running 89 or 90 octane in my car for many years without an issue (it says to put in 91.)

I use premium. The owners manual says to use premium. That’s what I use. If premium at the pump I go to today has 91, I’ll use that. If it has 93, then that’s what I get. Around here, the choices are regular 87, mid-grade 89, or 91-93 premium depending on the gas station. Assuming 10 gallons, if I played the half and half game I’d pay a total of 10 cents per gallon more. I’m not going to play cocktail mixer at the gas pump to save one dollar. If I needed to be that tight with money, I assure you I wouldn’t be driving an Acura. :wink:


#16

“Mix half 87 and half 93.”

This can save if a car is OK with 89-90 octane.
Typically mid-grade costs an extra $.10 for an additional 2 octane and premium costs $.20 for an additional 6 octane.

I did this way back when I had an '81 Accord with a modified engine (cam, weber, header etc.)


#17

My car tells me high octane is recommended, not required, but I run high octane regardless. Owner’s manual doesn’t specify using full synthetic oil, just 5w30, but I still pay extra for the full syn oil. I’d save maybe $3 a tank by switching to 87 octane and about $45 per oil change($27 vs $70), but I’m not risking a $7000 repair bill(Mazda would probably void my warranty if they found out I used 87 exclusively, or to just prove a point, who knows) to save a few bucks here and there; just isn’t worth it.

Why would I do this you ask? Surly I’m wasting my money by doing this right? 2 words: Turbo Charger.


#18

You realize, of course, that the engine has to knock first, before the sensor/ECM can retard the timing, and it will experiment by periodically advancing the timing again until it detects a knock again.

I’ve been driving company cars for years. Years ago I drove a Buick Skylark. It pinged lightly on regular unleaded so Buick told me to use premium fuel. The company that was paying for the fuel told me to use regular unleaded. That car, too, had a knock sensor, and it ran just fine until one day at about 60 thousand miles it burned a hole in one of the pistons. Apparently knock sensors don’t make engines immune from pre-ignition damage.

Your car, your choice.


#19

Hey guys, before you spend any more time on this, go back to the original question. Did you misread it? Rustylogic said he was sticking with 93 octane only because it had more DETERGENTS. He was not asking about performance, mpg, or knocking. Nor did he say anything about trying to cheap out.

So I suggest we all agree that he should stick with what he is doing: 91 or 93 octane, and then we can move on.


#20

Whether he was asking about engine damage or not, if he switches to 87, which he seems wont to do, he takes the risk of damaging his engine. As to what he’s doing, he drove on 87 for 400 miles. If he wasn’t interested in running 87, he wouldn’t have asked the question, and he wouldn’t have tried it for 400 miles. So what he’s doing is looking for someone to tell him nothing bad will happen if he switches to 87.

Now, since he thinks the only difference between 87 and 93 is a few HP, which he’s willing to sacrifice, it’s very logical to conclude that he’s interested in running 87 because it’s cheaper than premium.

And because he’s not the first, second, or 100th guy to come on here with a car that requires premium looking for someone to tell him it’s OK to run regular, our answers tend to be the same to everyone, which is “it’s 20 cents a gallon vs several thousand to replace your engine when you grenade it by doing what the owners manual told you specifically not to do. Don’t cheap out.”