TL Rower

Hi Folks, I did an advance search and found two postings on the issue of using regular vs hi test (super/93 octane) gas.

I started a new post as neither of the two previous posts pointed out any of the MECHANICAL issues one might encounter using regular octane gas where super is "required" and quickly deviated into personal pokes about if you could afford an expensive car, why would you use cheap gas.

I put super in my car so no flaming please. I'm just used to it; coming from Audi where nothing runs on regular. I'm just looking for objective technical reasons why super is required over regular beside providing better power and fuel economy.

People on the previous posts kept referring to "cheap" gas when talking about regular but there is a clear distinction. I have to assume that a "quality" gas distributor sells quality gas whether it be regular or super and the opposite for "cheap" gas distributors, so the term "cheap" i think should be removed from the conversation.

Let's assume that we're speaking of a quality gas provider.

What is the MECHANICAL detriment using quality regular gas in our 3.7L TL's compared to using 93 octane. Not looking for performance issues but mechanical.

Thanks!

MB

dwest1023

If premium is REQUIRED then the fuel mapping in the ECU is programed for higher octane
I am sure if you use regular the ECU would detune the engine to avoid damage. I would think over time the engine might not perform as well as it could if you used the recommended fuel.

draph

I've tested my TL SH AWD over a few tanks. While no audible knocking could be heard, and I didn't notice an appreciable drop in power, the fuel economy suffered enough to the point I've decided it wasn't really achieving any savings. ...and if a knock sensor is used to retard timing, I still don't like the idea of even the smallest damage a millisecond or two of knocking may cause before the computer takes action to protect the engine.

OTOH, the 2007 BMW 335i 6MT I leased before purchasing the 2010 TL showed absolutely no decrease in power, fuel economy, nor any knocking when running on 89 mid grade. Even the owners manual said 89 was "OK". I deduced BMW's approach to premium fuel with that particular car was more a marketing effort toward maintaining the brand's "all premium all the time" image, or they had plans to take full advantage of premium octane on a variant or future upgrade of the same engine without changing fuel requirements.

mynameisjacob

Nicely formulated question Rower... hopefully this will serve as the technical answer you are seeking:

As you may already know, Octane is used as a standard of measuring the gasoline's resistance to spontaneous combustion during the compression stroke of your non-diesel 4-stroke engine. Our engine, the Honda J37A4 has a compression ratio of 11.2 to 1 which is considered a 'high compression' engine.

If you fuel your tank with low octane 87 fuel, there is a possibility (which I believe is influenced by injected fuel quantity vs. intake air mass) that SOME portion of the fuel will experience early and spontaneous combustion while the piston head is still in its upward motion. Once piston head reaches apex, the timed spark ignites the fuel air mixture, exerting downward force to crank out rotational motion.

Ideally, you want to eliminate all premature combustion so that your spark plug can ignite the greatest amount of compressed fuel air mixture at its optimal peak of stroke. This would result in an ideal 'explosion' that occurs at the midpoint of the compressed space, radiating outward like a ball, exerting maximum downward force. However, when you do have premature combustion, it is out of sync with the spark and you create a scenario of opposing explosions clashing with each other like waves. This is 'pinging' or even worse 'knocking' of your engine. This causes carbon deposits on your cylinder wall, seals, fuel injector and valve heads. Over time these deposits accumulate and actually work to aggravate premature combustion, causing somewhat of a snowball effect of worsening conditions for your engine. This is your mechanical detriment right there. This is also where you lose MPG efficiency since your pre-mature fuel burns are not ideally working to promote rotational motion.

Now I'm not a chemical engineer but I'm pretty sure high octane does not equate to the "quality" of gasoline. Octane is merely (to put it VERY simply) the proportion of octane vs. heptane in the gasoline mixture. 93 Octane has 93% octane and 7% heptane... simple as that. Now, don't start throwing terms like isotopes and molecules at me because I'll just look back at you cross eyed... but I'm pretty sure its the same as saying 3 parts whiskey and 2 parts amaretto. Unfortunately, the general public has this misunderstanding (probably the result of sly marketing by gas chains) that cheaper low octane gas means higher impurities from poor refining techniques. Kinda like Johnny Walker Red vs. Blue. I'm pretty sure this is false.

The real way different gas brands become "Top Tier" and differentiate from others is by mixing their gasoline with detergents like Techron which helps keep the fuel distribution system and combustion chambers clean. The devious thing they do however, is only offer these detergent features in their highest octane offering... thus reinforcing the notion that higher octane means less impurities and cleaner engine.

It's definitely not a simple subject but I hope I answered your question. The moral of the story is... just put premium gas (greater than 91 Octane)... promoting optimization for your engine is never a bad thing.

KeithL

Here we go again. Simple answer, read the manual. If it says recommended then you don't need to use Premium, if it says required then not using Premium will likely lead to engine issues don the road. Infiniti 3.7 motors in the manual clear say REQUIRED and state it can cause damage if not used and that regular should only be used in an emergency, then only a 1/4 tank and then under light acceleration.

HeartTLs

iTrader: (5)

mynameisjacob, making it simple with whiskey terms

ucf_bronco

iTrader: (1)

Where in the manual does it mention specific details about the mechanical detriment of using a lower octane fuel?

Maybe you need to re-read the original post.

TeamAcura

mynameisjacob broke it down nicely. Basically any engine with a compression ratio of 10 to 1 or higher is considered high and will require high octane gas for the reasons mynameisjacob stated above.

TL Rower

Thanks Mom! (Keith), As Bronco pointed out, I never asked what the manual required or recommended for gas usage. Unlike most, I DO read manuals.

Thanks Bronco for pointing that out.

Thank you Jacob most of all for spelling this all out for us all in an orderly, concise manner!

MB

KeithL

My reference to damage was in Infiniti, as to the OP question, this is an on going never ending debate on fuel. Between the manual and sticking with top tier qualified fuel providers you should never have to worry about this topic. It has been proven numerous times that putting in higher octane than required or recommended has not benefit. Putting in the minimum required octane will not damage the engine/ It may not perform optimally, but the engine will last just as long. I'm not being MOM, I am just stating this boils down to a few simple things. As for cheap gas, well that is possible, but my guess is plenty of people put Costco,Kroger or any number of other no-name fuels in their car with no issues. At the end of the day gas from refineries and is piped to distribution points where trucks take it to stations. Some brand specific additives are added. Without a very tightly controlled experiment it is hard to prove the effects of a type of gas, as honestly other things like dirty/clogged air filters, faults fuel system components, etc can have a large impact on engine damage, particularly if not resolved in a reasonable time.

Mr Marco

Car Talk

OP search next time We already have several threads on the subject. This sort of stuff simply cloggs up the forum.

Bruce_Wayne

FYI, for anyone unaware, the manual says the car is "designed" (as opposed to required or recommended) to be used with premium fuel - 91 octane or higher. It also adds that regular grade - 87 octane - can be used temporarily, but regular use could lead to engine knocking and decreased engine performance.

BEAR-AvHistory

These systems all run on knock sensors to retard the ignition when you “run out” of octane. For a knock sensor to trigger you need some knock. Knock is the flame front smacking the piston crown too early. Regular smacking of the piston crown is not very good for the piston, piston pin or rod bearings.

Excess octane wastes money while under octane will reduce mileage/power & ring the pistons bell. A side note is premium fuel in many cases has a better additive package than regular which costs more to produce. About Costco..they have a list of stations that meet Tier one specs on additives.

Its unfortunate but 99% of these threads are by people trying to justify putting lower rated fuel in their cars. Maybe it makes them feel all warm & fuzzy to have some validation

justnspace

iTrader: (1)

^we also learned today in another thread in the 4G section that there are two ways to effectively raise octane.
Adding toluene
or
mixing 100 octane with 93 to make some where in the middle.

"octane boosters" that are sold at gas stations and auto parts stores are snake oil.

KeithL

I believe that is a myth, most reputable brands will but same additives in all grades

shinyknight

Found this informative video; which show it visually (start at 2:00)


Now, for the mechanical part: as already well explained; if your fuel goes off before reaching the apex of the run, you will cause force downwards. Per se is not bad on the piston, but it is bad on the crankshaft and connecting rods.

The loss of power is due the fact that if the fuel burn and does not explode, part of it's energy is just wasted as heat, instead than converted in motion.

The main problem is on the structural integrity of the engine: you are transmitting force while part of it is at an angle (you may notice that the explosion happens mainly when the surface of the piston, connecting rods and the crankshaft are perfectly aligned..there is a mechanical reason for that, to transmit the force downward and avoid stressing the material); which is why you can cause problems on the engine. The flywheel moves a bit the crankshaft, so the energy gets transmitted from the piston down to the crankshaft (if this won't happen, your engine will just crack under the downward force).

Engines are simple conceptually, but they are very complex when you think about timing of all its parts....between valves that open and close, sparks that happens at a certain time, and crankshaft that has to keep up with the rest of the procedure, if you change any of these values, you carry over the delta until it gets noticeable (and your engine will let you know, either by moaning or by loosing power)

The fact that you loose power is irrelevant IMO, compared to the possible damage that you may cause to the engine itself. Of course 1 week on regular won't kill your car (unless you are racing on a track, or pushing the engine to the red), but it is good habit to avoid it, since nowadays the car has a computer that is set to mix and regulate the engine output based on the assumption of the fuel octane ratio....if you make a cake and put too little yeast, then of course the result will not be what you expect.

So to summarize: yes, you may damage the engine, but it is most unlikely that you will break the crankshaft or the connecting rods if you do it once in a while; altho you just throw off the whole car fuel system and engine timing, which may bring a lot of smaller but still problematic issues on the long run.

The dealer told me "if you can't afford premium, don't buy the car", when I asked him what kind of fuel it takes; which I think makes totally sense, now that I know how the whole thing works

Hope this helps

BEAR-AvHistory

You certainly have that right Thing is the additive package is the only thing that separates brand A from brand B since most fuel comes from unified refineries. Federal law requires a minimum level detergent package but Tier One fuels exceed those basic requirements. Tier One are a group of brands recommended by the high performance auto manufactures for their cars. So in the case of these cars you not only get a octane recommendation by also a series of selected brands.

Costco runs five times the EPA mandated minimum in both Premium & Regular. Many second tier stations run extra in Premium but minimum in regular. Discount stations just buy what ever they can get the cheapest.

BEAR-AvHistory

"""Now, for the mechanical part: as already well explained; if your fuel goes off before reaching the apex of the run, you will cause force downwards. Per se is not bad on the piston, but it is bad on the crankshaft and connecting rods.

The loss of power is due the fact that if the fuel burn and does not explode, part of it's energy is just wasted as heat, instead than converted in motion."""

I have some problems with both these statements.

In all engines the fuel is ignited before the piston reaches top dead center (TDC). The higher the engine performance the more "lead" the ignition takes. This lead is how far in advance of TDC the plug will fire as expressed in degrees.

Second thing is "exploding" fuel mixtures are bad news especially for high compression engines. There is a lot of chatter about octane numbers but no one ever says what it does. The higher the octane level a fuel has the slower it will burn.

This slow burn allows longer ignition leads for high output engines. Fuel exploding just creates knock which is why low octane fuel which will explode in high compression motors is a bad plan.

Quick edit. Anyone who says knock will not bother a piston has never seen a piston with a hole blown through it.

Mr Marco

jim_c

Not to be too picky but part of Jacob's "explanation" way above here is not correct. The ignition timing, i.e. when the spark plug fires in relation to the piston's position, is almost always significantly advanced. The spark plug fires before the piston gets to TDC (top dead center) when it is running properly. The engine does not "wait" for the piston to reach tdc and then fire the plug. As has been pointed out, knocking (also called detonation) results when the fuel/air mixture ignites due to compression heat and its uneven, uncontrolled nature is the problem. The act of compression causes the mixture to get very hot and a lower octane fuel is unable to resist the urge to ignite prior to the spark plug firing. Higher compression engines cause greater heating of the mixture.

mccvii

So, here's what I don't get. This conversation has been going back as long as there's been super unleaded which I guess was about the time that the EPA took the lead out of the gas. That said, I'm still confused. Every thing I hear is "if the compression ration is over 10:1, you have to use premium or else" but then there's this data:

The 2013 3.7 V6 Mustang that delivers 19/31 MPG, makes 305 @6,500, 280 @4,250 ft. lbs torque with a compression ratio of 10.5:1 and recommends Regular (87 Octane gas).

Cadillac makes the 2013 CTS with a 3.6 V6 that gets 18/27 MPG and makes 318 @ 6800 rpm, 275 @ 4900 rpm torque with a compression ratio of 11.5:1 and recommends regular (87 Octane) unleaded.

The dog of the bunch is the 2013 Chrysler 300 3.6 V6 that gets a respectable 19/31 MPG while producing 292 @ 6350 rpm, 260 @ 4800 rpm ft. lbs torque with a compression ration of 10.2:1 while recommending Regular (87 Octane) fuel.

The 2013 Acura TL with the 3.5 V6 earns a 20/29 MPG fuel rating while making 280 @ 6200 rpm, 254 @ 5000 rpm torque with a compression ration of 11.2:1 and recommends Premium (91 Octane) fuel.

The 2013 Honda Accord EX-L with a 3.5 V6 gets 21/34 MPG, makes 278 @ 6200 rpm, 252 @ 4900 rpm torque with a compression ration of 10.5:1 and recommends, you guessed it, 87 Octane, regular unleaded.

So, am I the only one confused here? How can Ford, Chrysler, and GM make a 6 cylinder engine that produces 290+ HP with compression ratios exceeding 10:1 (by quite a lot in the case of the CTS) while still maintaining similar fuel economy to the Acura? Do they know something that Acura doesn't? I could go along with that notion right up until I get to the Accord with the V6 3.5 that makes 2 HP shy of the TL but sporting a 0-60 time in the 6 second range (6.1 according to Edmunds) - about the same as the TL. Some results have the Accord holding a slight improvement over the 3.5 Acura. So, I'm confused again.

I love my Acuras. I've had 3 in the last 10 years and looking at # 4 as we speak. I've had great luck and lots of miles regardless of the fuel I've put in the tank. But, there's still that lingering belief that I'm doing something wrong and that a car that produces the kind of power that my "luxury" car offers can't possibly run on lower octane fuel and I am a cheapskate for even considering. Of course, the competition disagrees as they produce similar performing cars that don't carry the badge or the stigma for disregarding.

I hate that I find myself feeling like this is more brand differentiation and marketing than actual fact unless the Ford, GM, Chrysler, and Honda numbers are fudged.

Does this make sense to anyone? Why can't Acura, Lexus, MB, BMW, Audi, and Volvo (LOL) make a performance car with higher compression ratios that doesn't require a premium fuel recommendation (or requirement) when its clear that its not only possible but practical?

jim_c

This is an interesting discussion. If you're not into the technical basis, just ignore it. FWIW I don't really believe the part about detonation (also called knocking, pinging, preignition) causing a significant amount of carbon buildup in modern engines. It was definitely true years ago that engines would carbon up but those old carbureted inefficient beasts were totally different. The statement about loss of efficiency through heat loss is also questionable. I would think most of the losses would relate to incomplete combustion, i.e. not all the fuel becomes CO2 and H2O which is what happens in theory. The power to drive the pistons comes from the fuel and air mixture burning. The exhaust gases are very hot and importantly the no. of molecules in the exhaust is about 25% greater than in the fuel air mixture. PV=nRT.

I use a combination of octanes 89 and 91 in my 3.5L TL and have never experienced knocking or detected any lack of performance. (I realize there may be some differences happening that are subtle.) It cost me $80 in Canada for a fill and $45 in the U.S.

KEYFRAME13

I looked over those myself a month back and got it that all the luxury manufacture wants you to believe you own a premium car to make you feel special and pay more for that.
I have a lexus IS250 and also require premium and after long debated I decided to put 87. I have a month and a half since I did that and I must say not only i felt no decrese in power but my mileage increased somehow. I used to get 23mpg with premium and now with 87 i never saw it under 25.5. It's the opposite I read and many on Lexus forum experienced the same. I thought I'll just try it but I might just stick with 87.
P.s. i never heard of an engine breaking from using 87 octane, I challenge everyone to come with a proof of that.

614Banker

My understanding is that the higher grade gas is meant to primarily help preserve your catalytic converters; and some say help in performance. At least that was the case with my previous car which was a Range Rover. So I just assumed that was case with Acuras and other premium autos and never thought to question it. The prolonged use of regular gas was associated with faulty cat-converters in Range Rovers resulting in failed e-tests.

ac011

iTrader: (1)

Most peoples with lease vehicle use regular gas. I don't think there will be any damage to the car but few HP less.

C8N

I took my car to the dealer twice for noises I thought were irregular and both times, the first thing the SA asked was what octane gas I put in my car without asking any other specifics.

Even if I knew nothing about cars, just based on this experience alone, this leads me to believe that octane does have some sort of significances in the way our cars perform.

C8N

This is one of the reasons why I went with a new car rather than buying a CPO and saving some $$ as most are lease turn ins.

jim_c

Last couple posts sort of sound logical, but I'm a bit sceptical.
Would they use different cat converters on the cars that call for high test?
The reason the tech asks you about your gas purchase is because it is easiest thing to do, it deflects the problem back to you, gives him something to blame if he can't solve the problem otherwise.
And what evidence do you have to support the claim about what other people use in their leased vehicles?

Yikes

Gay-Lussac's gas law roughly tells us that the pressure of a gas and its temperature are directly related. Simply put, when you increase the pressure of a gas, the temperature increases. (This is the fundamental principle that diesel engines are built upon)

Octane rating simply means resistance to burning.

On an engine with higher compression, this means that the gasses inside the combustion chamber are subject to a lot higher pressure. If you run anything lower than 91 octane you run the risk of having the fuel ignite, simply because of the temperature caused by the amount of compression, before the piston reaches TDC. This will try to force the piston down when it is trying to move up. Needless to say this will not only result in a loss of power, but could also damage engine parts.

Guys in the 3G forum have noticed engine knock of long periods of 87 usage.

C8N

Well... it probably will not carry much weight with others but I have to say 2 out 3 people I personally know who lease, cheese out on gas

User Error

Oh my god all the answers are insane the simple and real answer as to why some car's require premium fuel is they have high compression pistons and require a stronger combustion to run efficiently and allow the piston to make a proper "stroke"...

KEYFRAME13

Modern engines have a knock sensor that when the regular gas is detected it adjusts the engine timing to avoid knocking. So most probably you won;t hurt the engine. This happend in the past with the engines that don;t have this knock sensor.
Performance wise they say you only lose half sec 0-60mph so most people won;t feel that.

jim_c

Wow, you sound like a real auto engineer! NOT! LOL! A proper stroke eh......a stronger combustion eh....

If it's that simple, tell me about the new Mazda6 which has 13:1 (yes, 13:1) compression, and requires regular gas only.
Actually, for a terrific read on this subject, please have a look at the Mazda Skyactive site. Very interesting and readable technical description of this whole topic and how they are approaching it.



Most questions have simple easy to understand wrong answers!

Mr Marco

With the current level of ethanol that is added to my gas...I notice. My SHO would stall at take-off without the proper octane loaded. Aaaaand that's the last time I lent my car out to a co-worker.

weather

Not that my post really matters but for the record, I always put "supreme" or high octane in my Acuras. I know there is an ongoing debate between the value of such gasoline vs the fact that some say its a waste of money.

For me, where I live, its about 3$ difference per tank, with an average of 3 to 4 tank a month....9-12$ a month so really, its not even worth giving it any second thoughts. I am not trying to say that people should or shouldn't, I am just saying that in MY situation, its a no brainer......and for the record....I lease my TL and own the RDX but even if I leased the RDX, supreme gas would be in anyway.

BEAR-AvHistory

10:1 = Premium fuel is a pre computer control rule of thumb that is not valid with variable valve timing & direct injection engines of today. You will not find any 10.5/11.0 compression ratio engines from the muscle car era that ran on regular.

Look up the difference between static vs dynamic compression ratio

Cygnus_X1

I'm with you on this, I figured out it cost me an extra $12 a month to use premium gas. I don't even give it a second thought and my TL is leased.

C8N

I wish more people were like you guys.

To be completely honest... if I leased, I probably would have cheesed out on gas.

jim_c

My interest is almost entirely "academic". Perhaps we have digressed from what the OP was asking, not sure. The point now - so far as I'm concerned - is : what are the engine design and engine operation variables that determine whether it will knock or ping on a particular grade of fuel. As I mentioned, The Mazda site has a very interesting discussion of factors that no one has brought up in this thread which I won't bore you with right now. I have driven plenty of cars that exhibited engine knocking or preignition in the old days but as Kevin suggests, it is pretty rare now. Modern cars are approximately a million times better than the crap we had to drive in the 60's, from a technical perspective. As a general rule though, I do believe it makes sense to follow the manufacturer's recommendation regarding fuel and some other fluids. But again, I always like to know "why?"

Franco2112

It is safe to say that the car manufacture has an octane rating to give you the best performance for that vehicle. Now to say that we all get the same stated octane at every gas station is somewhat of a quin-dry. Some vehicles will run better on Chevron and others on Shell. It is up to you to choose the best fuel for your car so. Also throw in the fact of Ethanol is added to most fuel (10%) by secondary shippers an may change the way rated octane performs on your vehicle. If more than 10% is added, Ethanol will draw water away from pure gasoline and create a water layer. You got, bad gas! I use Chevron supreme with Techron in my TL and it performs great. The day it stops performing well on that fuel, I'll search again. Hope that day never comes.