Premium vs. Regular: Addition to the FAQ:

Maintenance/Repairs
21

To Steve F. Here is the poster’s question:

“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”?”

87 and 91 - 93 do burn differently. I don’t buy the carbon build up theory the dealer is pushing. But, the difference in burning can cause engine damage, namely holes in pistons. Knock sensors reduce the incidence of damage due to pre-ignition. However knock sensors can and do fail, and some knock sensors can’t adjust timing enough for heavy load conditions.

I don’t see the replies as out of order given the question by the OP.

22

For everyone who has stated that using 87 in my vehicle will damage the engine, please re-read my post:

“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.”

My question is solely concerning carbon buildup, and why this might be. I thought it was due to detergents, but the dealer is telling me its due to how the gasoline burns differently in the engine. It’s not clear to me if this is true or not, and if it is true, some type of explanation as to how this is.

As far as MPG testing goes, it was on the same roads on my way to work, during the same time of year, using the car’s measurement. So, one would expect the measurement to be consistent, at minimum, hopefully.

23

Also, please read the CarTalk site before replying to this post, too:


Now the CarTalk guys have also posted:

Which was additional evidence to make me believe the increased carbon buildup theory may also be “booooogus”

Also see:

Given the information on this website, and my car’s good behavior using 87, I don’t see a reason not to use 87, unless the dealer is correct about carbon buildup, which is why I’m trying to answer this question.

If you don’t have a comment about carbon buildup in particular, please start a different thread, as it does not address my question.

24

An additional piece of information: the difference between 87 and 93 at my local gas stations varies from $0.40 to $0.50 per gallon. I have a 17 gallon tank, and I drive 100 miles per day, round trip.

25

For everyone who has stated that using 87 in my vehicle will damage the engine, please re-read my post:

I did.

“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.”

So we’ve established that the guy who told you this is full of crap about the carbon deposits (btw, a hint for this genius - the higher the octane, the MORE carbon deposits you’ll build up if you build them up, because it’s more resistant to burn and therefore more likely to burn incompletely). Since we know he’s full of crap about that, it’s not out of line for you to recognize that he just might be full of crap about it damaging your engine.

My question is solely concerning carbon buildup, and why this might be. I thought it was due to detergents, but the dealer is telling me its due to how the gasoline burns differently in the engine. It’s not clear to me if this is true or not, and if it is true, some type of explanation as to how this is.

As I said above, he’s full of crap. It has nothing to do with carbon deposits. Nothing. This guy, whoever he is, has no idea what he’s talking about. That’s not surprising. The service manager at my Acura dealership blithely informed me that my car both sends and receives vehicle data from Acura’s own satellite, despite the fact that in order to legally transmit to a satellite you have to have an FCC license to do so, and the required equipment, none of which any Acura has.

Were I you, I would make very sure that this guy never so much as puts air in my tires, because not only does he not know what he’s talking about, but he THINKS he knows what he’s talking about, and that makes him very dangerous.

And what we said above stands. If you do this, you risk damaging your engine. What you do with that information, is up to you.

26

Another Reginald Denny beating over premium fuel.

Shadowfox answered the carbon question, service writers don’t have answers to tough questions and rely on myth. You may experience the same carbon build-up as other cars that normaly use regular unleaded, unless there is something unusual about an Acura engine.

I have seen carbon build-up in cylinders become a problem in the early ninety’s, carbon on the piston and cylinder head reduced the cleaance to zero resulting in an annoying knock. The fix was a software update and a decarb proceedure.

During the last 22 years at new car dealers the only “holes in pistons” I’ve seen were when a car was driven 75 MPH with no coolant in the engine. 1998 Dodge Ram 5.2, 5.9L engines had a serious spark knock problem until a software update was available, I’ve never seen engine damage as a result, just angry customers.

Knock sensors work and people do put the wrong fuel in cars. I have drained diesel and E85 from about 50 fuel tanks. I believe there are many more errors with 87/93 octane.

I have another uninteresting picture for you. At the Lexus dealer they have about 60 loan cars, the fuel for these cars comes out of this pump. This pump is also used to fill new cars, used cars and customer cars during a recall visit. Most Lexus vehicles are labeled “Premium fuel Requiered”. I don’t know what is in the tank, I am only guessing.

27

The owner’s manuals are written by technical writers who get their requirements directly from the design package that comes from the design team. The design package is only finalized after computer modeling is done that includes the way heat will propogate in the cylinders and stresses will be absorbed. The design is supplemented by countless tests, including accelerated life testing with countless monitors, whereinafter engines are torn down and in depth analysis done of their parts and performance, as well as countless hours of actual track testing, again followed by teardown and analysis.

If you choose to ignore their requirement of premium fuel and run 87 octane instead, you do so at your own risk. Personally, I’m inclined to believe that the requirement is there as a result of lots of engineering and testing. I believe it’s folly to ignore it.

So, I’ll make this simple. Assume that the engineers in all their analysis and testing found some reason to require premium fuel. Or save your pennies, because you may find out the hard way why they required premium.

28

I have another uninteresting picture for you. At the Lexus dealer they have about 60 loan cars, the fuel for these cars comes out of this pump. This pump is also used to fill new cars, used cars and customer cars during a recall visit. Most Lexus vehicles are labeled “Premium fuel Requiered”. I don’t know what is in the tank, I am only guessing.

My wifes Lexus says it’s recommended to use Hi-Test…NOT REQUIRED.

29

rustylogic - you’ll note that C&C’s answers contain lots of ‘weasel words’, like ‘probably’, ‘not likely’, that kind of thing. Follow their recommendations if you like, just know that they have little more factual insight into this issue than most posters here.

For example, they say:
“We don’t believe that any modern engine that claims to require premium will be damaged by using regular unleaded judiciously. Neither do any of the sources we’ve checked with — including the American Petroleum Institute, the American Engine Rebuilders Association — even a chemist (who would rather go unnamed) at a major gasoline company.”

None of their sources include the car makers that often require premium. That’s who I’d want to hear from. And notice the word ‘judiciously’ tossed in there, as in ‘it depends’, or ‘usually’. I would espcially not use regular in a turbo car that ‘requires’ premium, something C&C fail to address.

I use regular in my Lexus (‘premium recommended’) with no ill effect. In contrast, your manual plainly states that engine damage may result with regular, right?

Just not worth the $$ to me.

30

I don’t understand why anyone would spend a lot of money on a nice car and then decide to disregard the manufacturer’s recommendations.

Especially when the manual states that damage may result if you don’t follow a recommendation.

Why not disregard the oil change intervals and other recommendations also?

It makes just as much sense.

31

91 resists detonation more than 87. The knock sensors (vibration sensors really) will dial back the timing for 87, but the potential for damage has ALREADY occurred, and this would happen EVERY time you fire up the car - kind of like gambling on whether or not your piston burns this turn of the key, but hey, it’s your car, and maybe you have the money to reload a new engine into it every few years. Anyone recommending going against the manufacturer’s requirements should be ignored, unless you actually know better than the teams of engineers that designed it.

32

“Why not disregard the oil change intervals and other recommendations also?”

Lots of people do…