Do I really must use premium gas?

[Andy T]

What really happens if one uses regular gas instead of premium in a car on a regular basis?
This is a topic I been coming back to over the years. I have 2010 Lexus RX 350 and 2017 ES 350. Both mention to use "premium". However, in the 2010, I use regular more often without any visible issues. Occasionally, I would also use ethanol free gas.
What makes "premium" gas premium, and why some car manuals state to use it?

[PNWTO]

https://www.reddit.com/r/askscience/comments/nfhid5/what_if_any_are_the_benefits_of_using_premium_gas/


Not a direct answer but an explanation of the “rating”. FWIW, but not Japanese, I never used premium in three different Audis and never saw any ill-effect, and I was finicky about those things.

You’ll see a lot of chatter and even some mechanics disagree.

[RevolverRob]

Short Answer is: Maybe.

Longer Answer: You'll have to evaluate if your particular vehicles have significant differences in fuel economy (the best indicator for efficiency changes), and/or are notably down on power. If not then you probably don't need premium, particularly at sea level.

Longest Answer: Understand what octane does - Increased octane allows more timing advance to happen prior to detonation (knocking) occurring. Detonation is when then air/fuel mixture is ignited not by the spark plug, but by burning vapor still present in the cylinder.

Remember what an internal combustion engine is - it's a big air pump. Octane helps resist detonation, reducing (eliminating) knocking - this let's the engine run more timing (more efficient mating between spark plug and air/fuel ratio). In a perfect world, timing is set at the point at which the cylinder is perfectly filled with the correct amount of compressed air/fuel such that the ignition causes 100% combustion. That is not only physically impossible, but also impossible given varying load conditions placed on IC engines. To compensate, variable timing has existed for more than a century. Today, it's controlled by many sophisticated sensors and much better than back in the day. But even still, extra octane can allow the engine to run more timing, producing more power and more efficiency.

It maybe counter-intuitive, but an engine makes all the power it is capable of making at maximum efficiency. That's all "tuning" really is - finding places to improve engine efficiency. So, if your engine can resist knocking and have more timing, it will be more efficient (to a degree). Because physics and real world, it's never perfect.

[BehindBlueI's]

In modern engines you can get away with running lower octane fuels because the computer will retard timing based on input from knock sensors before damage occurs. However, retarding timing costs you power and efficiency. Climing a steep incline in scorching summer heat is not the same as idling along on city streets in mid autumn. In the first scenario, you'll certainly see a difference as the heat soaked engine that's working hard will start to have knock earlier with lower octane fuel. In the second scenario, you'll very unlikely to note a difference.

I run premium in my Camaro because that's what the LS3 calls for and I don't want my car going to the low octane timing charts. I bought the HP I paid for. Same reason I ran mid-grade in my 5.7L Hemi equipped Ram. My 6.4L Hemi equipped Ram calls for 87 because the lower compression means the motor won't take advantage of the higher octane, as the 6.4 is built with a bias for longevity over outright performance.

[0ddl0t]

What really happens if one uses regular gas instead of premium in a car on a regular basis?
This is a topic I been coming back to over the years. I have 2010 Lexus RX 350 and 2017 ES 350. Both mention to use "premium". However, in the 2010, I use regular more often without any visible issues. Occasionally, I would also use ethanol free gas.
What makes "premium" gas premium, and why some car manuals state to use it?

Toyota uses the exact same block assembly (11401-09600) and head assemblies (11102-09142 & 11101-09262) in the 2010 V6 Camry as Lexus does in the 2010 ES350, but Toyota specifies 87 octane while Lexus says to use premium. Lexus does use a different ECU/PCM ( part number 89661-33E72 vs 89661-33E61) suggesting it gets a bit sportier tune allowing it to make a bit more power & torque:

The 2010 Lexus ES350 was rated at 272 hp @ 6200 rpm and 254 lb-ft @ 4700 rpm
The 2010 Camry 3.5L was rated at 268 hp @ 6,200 rpm and 248 lb-ft @ 4,700 rpm


Every Lexus manual I've seen says you can use 87 octane if nothing else is available, but to use premium normally. I imagine it won't make a difference in whether the engine makes it 100,000 miles, but it may affect whether you make it to 300,000 on original head gaskets.
Modern ECUs can detect the slightest knock and detune the engine to protect it, but only after knock has occurred. Hundreds of thousands of miles of these minute knocks can cause head bolts/studs to stretch and the head gasket to fail (more severe knocks can harm the piston & rings, but on Toyota it is usually the head gasket that fails)

[RoyGBiv]

I put premium in my 87 octane car a few months ago (skipping the why)
Got worse gas mileage and the stink from the CAT took 2 more tanks to get rid of.
Don't do that!

[TGS]

JRB more than a few things for you to dissect here

[Spartan1980]

If your car has forced induction I'd strongly recommend against using anything lower than recommended. I've seen two of my former bosses crater engines because they put regular fuel in them. Both supercharged.

One was a Ford F150 Harley Edition. That one actually got replaced under warranty but I know it was simply the dealer doing it because of who he was. We told him it would happen but he didn't believe us, he said it "ran fine". 8k later he had holes in 3 pistons.

The other one was a factory ordered big block Chevy Suburban 4X4 with a Whipple bolted on after delivery. He loaned it to his sister and forgot to tell her about the gas. That was a painful mistake.

[JohnO]

If your car has forced induction I'd strongly recommend against using anything lower than recommended. I've seen two of my former bosses crater engines because they put regular fuel in them. Both supercharged.

One was a Ford F150 Harley Edition. That one actually got replaced under warranty but I know it was simply the dealer doing it because of who he was. We told him it would happen but he didn't believe us, he said it "ran fine". 8k later he had holes in 3 pistons.

The other one was a factory ordered big block Chevy Suburban 4X4 with a Whipple bolted on after delivery. He loaned it to his sister and forgot to tell her about the gas. That was a painful mistake.

I had a buddy back in the 1980's who had a Saab 900 Turbo. He monkeyed with the wastegate and the boost ran much higher than factory spec. The car pulled HARD under boost! He sold it to a friend who knew what he was getting and liked the fact that the car had great performance. Within a couple months the new owner had a trashed engine. There was so much pre-detonation due to the increased boost that holes were burned through the pistons.

[HeavyDuty]

I put premium in my 87 octane car a few months ago (skipping the why)
Got worse gas mileage and the stink from the CAT took 2 more tanks to get rid of.
Don't do that!

I have a 2006 Miata that prefers premium. I had to put a tank of regular in it on a long drive and noticed an immediate performance hit, it came back a little as the car relearned things but it was much happier and back to normal after a few tanks of premium again. I started keeping a bottle of octane boost in the trunk after that.

[pangloss]

A car enthusiast and body shop owner once told me that "premium gasoline is life's cheapest luxury." That was a over a decade ago and the last time I complained about paying for premium.

Sent from my moto g power (2021) using Tapatalk

[JRB]

RevolverRob and BehindBlueI's deftly addressed the meat and potatoes of what's going on and 0ddl0t addressed it nicely to your Toyota situation.

If a turbo or supercharger is involved, Premium fuel is not optional, it's mandatory. If it's a higher HP performance engine, again, it's not optional, it's mandatory.

Your particular engine in the RX350 is a somewhat popular engine swap for older Toyota MR2's, and it's been noted that the Lexus ECU tends to make 5-10 more HP on a chassis dyno. These guys all run premium 100% of the time though. I'd expect knock count response in that ECU to be fairly aggressive as Toyota tunes those so Suzy Soccermom can fill it with 86 octane and merge into 75mph highway traffic when it's 110* outside, and not end up with a warranty claim for a new engine. That said, the warranty duration is carefully considered and as 0ddl0t addressed, long-term reliability can often be compromised by running lower grade fuel. The engine and everything else may survive the warranty period, but if you really want 300k+ mile service lives out of your Toyotas its best to use the gasoline spec'd and virtually every Lexus model calls for 91+ octane premium.

Premium gasoline is the most consistent and subject to the highest storage and consistency standards. On the sourcing/bulk supply side, if premium gasoline doesn't meet spec, it is usually downgraded & blended into to midgrade or regular. Regular 86 octane that doesn't meet spec is usually blended with 'good' 86 octane until it meets minimum spec. So if you're wanting the cleanest and most consistent fuel at any given gas station it's the premium gasoline pump - assuming that station's storage tanks aren't compromised somehow.

Yeah, it sucks to pay another $10-20 a tank at the pump, but the cost savings of regular disappears pretty quickly with a single shop visit.


I had a buddy back in the 1980's who had a Saab 900 Turbo. He monkeyed with the wastegate and the boost ran much higher than factory spec. The car pulled HARD under boost! He sold it to a friend who knew what he was getting and liked the fact that the car had great performance. Within a couple months the new owner had a trashed engine. There was so much pre-detonation due to the increased boost that holes were burned through the pistons.

I'd bet $100 that new buyer filled it with 86 octane, or got greedy and bumped the boost up more. The detonation threshold for a turbocharged engine is a very 'all or nothing' sort of thing, and either it'll be reliable and holding together just fine on a given tune+fuel combo, or the fuel will be insufficient in which case bad things happen VERY fast to the engine. I know this from personal experience on more than a few occasions :X


I put premium in my 87 octane car a few months ago (skipping the why)
Got worse gas mileage and the stink from the CAT took 2 more tanks to get rid of.
Don't do that!

That's strange - what's the year/make/model of that vehicle? Which engine does it have?
Engines that are truly set up for 86 octane bottom-rack chicken piss won't get any performance or MPG benefit from premium, but worse mileage and a strange smell makes me suspect bad fuel.


A car enthusiast and body shop owner once told me that "premium gasoline is life's cheapest luxury." That was a over a decade ago and the last time I complained about paying for premium.

Accurate! I'll probably be stealing that saying... :)

[Darth_Uno]

I put premium in my 5.7 Tundra now and then, for no real reason. I do get better MPG, but that's obviously offset by the cost of premium, so overall pretty much a wash.

[David S.]

Any thoughts on use of regular vs premium for daily driving a 3.5L Ecoboost F150. I drive with a very light foot and would use premium for towing. This is a truck I'd like to see go 200+k miles.

Also, thoughts on "Top Tier (https://toptiergas.com/licensed-brands/)" gasoline?

[Andy T]

Is there a benefit of using lower grade (88) Ethanol free gas vs higher grade premium gas.

[Jim Watson]

My BMW book says to use 91 octane, that 89 is safe but will adversely affect mileage and performance.
I have topped it up for a trip with 89 and no perceptible effect, but a fillup from <25% sure enough, reduced the mileage. I wasn't pushing hard enough to tell if it hurt acceleration.

I fancy it runs smoother on teetotal gasoline but the only nearby station with 91 EtOH free is suspect, I have twice had my credit card hacked after a purchase there.

My van gets better mileage on 87 EtOH Free but not enough better to pay for it.

[RoyGBiv]

That's strange - what's the year/make/model of that vehicle? Which engine does it have?
Engines that are truly set up for 86 octane bottom-rack chicken piss won't get any performance or MPG benefit from premium, but worse mileage and a strange smell makes me suspect bad fuel.

2015 Volvo S60 2.0L 4-Cyl

Actually, the sulfur stink was coming through the AC vents more than from outside....

Fuel was from Kroger... we had a bunch of points ($1/gal discount) and filled up wifes car (requires premium) and mine from the same pump. Never had a problem with their gas previously, but, there's always a first time.

[0ddl0t]

Any thoughts on use of regular vs premium for daily driving a 3.5L Ecoboost F150. I drive with a very light foot and would use premium for towing. This is a truck I'd like to see go 200+k miles.

Also, thoughts on "Top Tier (https://toptiergas.com/licensed-brands/)" gasoline?


I'd run premium in the ecoboost unless I was a bean counting businessman driving high miles at light loads (in which case I probably wouldn't be driving an F150).

I would definitely get top tier gas. You don't have to spend more for it - many cheap stations (ARCO, Costco, Valero, etc) are Top Tier

https://www.consumerreports.org/fuel-economy-efficiency/top-tier-gasoline-worth-the-extra-price-a7682471234/

[0ddl0t]

Is there a benefit of using lower grade (88) Ethanol free gas vs higher grade premium gas.

Pure gas should get about 3% better mpg than E10 and be more stable if you park for long periods of time, but it won't make more power at the same octane rating and may make less if you are comparing 88 pure gas vs 91-93 E10 (depending on whether your is tuned for higher octane car).

[whomever]

Here is what Ford says for my 2018 2.7 Ecoboost (which is of course turbocharged):

"Your vehicle is designed to operate on regular unleaded gasoline with a minimum pump (R+M)/2 octane rating of 87.

Some fuel stations, particularly those in high altitude areas, offer fuels posted as regular unleaded gasoline with an octane rating below 87. The use of these fuels could result in engine damage that will not be covered by the vehicle warranty.

For best overall vehicle and engine performance, premium fuel with an octane rating of 91 or higher is recommended. The performance gained by using premium fuel is most noticeable in hot weather as well as other conditions, for example when towing a trailer. See Towing.

Do not be concerned if the engine sometimes knocks lightly. However, if the engine knocks heavily while using fuel with the recommended octane rating, contact an authorized dealer to prevent any engine damage.

We recommend Top Tier detergent gasolines, where available to help minimize engine deposits and maintain optimal vehicle and engine performance. "

https://www.fordservicecontent.com/Ford_Content/vdirsnet/OwnerManual/Home/Content?variantid=4640&languageCode=en&countryCode=USA&Uid=G1780457&ProcUid=G1717126&userMarket=USA&div=f&vFilteringEnabled=False&buildtype=web


Some comments:
1)The <87 octane thing at higher altitudes is real. IIRC in, e.g., Great Falls MT the choices at some stations are Regular=85 octane, Mid=?88?, Premium=93, so watch for that.

2)The '87 is OK but 93 gives better performance' bit is because the vehicle has knock sensors and detunes itself as needed (elsewhere in the manual, it notices when you fill up, and the engine controls experiment after you fill up to see what they can get away with with this particular tank of gas, then runs those settings until you fill up again).

3)If you have an engine old enough that it doesn't have knock sensors, you must use the specified octane (or higher, but higher won't get you better performance), or Bad Things will happen, like holes in your pistons, etc, etc.

4)I use 87, because I don't care about performance other than MPG. It may be that you can get more MPG with higher octane, because the controls will use more boost/different timing/whatever. I have seen posts on Ford forums where people experimented and found that for their vehicle that they minimized cost by buying premium when the cost difference between 87 and 93 octane was less than XX cents per gallon. My recollection was that XX was usually less than the price difference I see at the pump, so I never did the experiment.

I might reconsider if I was going to be going 80 in hot weather or something.

[0ddl0t]

I've read the 2.7 ecoboost isn't as affected by 87 octane as the 3.5 - where it is quite noticable.
Car & Driver tested premium fuels on a handful of vehicles and it made the biggest difference on the 3.5 F150: https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/ )

97319

[JRB]

Is there a benefit of using lower grade (88) Ethanol free gas vs higher grade premium gas.

On older vehicles & small engines (like old lawnmowers) not designed for E10 or any other Ethanol-blend fuels, absolutely. A buddy of mine had an old '85 Toyota 4Runner and the difference between E10 and Ethanol-free mid-grade was astonishing; it got around 3mpg better mileage and made noticeably more power with Ethanol free fuel. The primitive EFI system in that truck simply had no way to adjust for E10. So while the octane rating was fine and no damage was done, the energy density was much reduced and the ECU couldn't adjust fuel trims accordingly. So he sought out Ethanol-free fuel as much as he could while he had it.

Modern vehicles that can run E10 without issue, or were designed for E10, will get virtually no benefit to Ethanol free, aside from it being more stable for long term static storage because the Ethanol is hygroscopic and attracts water contamination.


Any thoughts on use of regular vs premium for daily driving a 3.5L Ecoboost F150. I drive with a very light foot and would use premium for towing. This is a truck I'd like to see go 200+k miles.

Also, thoughts on "Top Tier (https://toptiergas.com/licensed-brands/)" gasoline?

Turbos = premium gas all the time, IMHO. If you want max reliability out of an Ecoboost I'd also strongly suggest quality oil changes every 5k-6k miles with good filters, and spark plugs every 20-30k miles.

Buying a vehicle with a modern high technology turbocharged engine, only to feed it the cheapest lowest-octane gas you can find, is not unlike buying a $5k custom 1911 and feeding it cheap Russian steel case ammo. Sure, it might work well enough for you -for some time even- but you're compromising performance for sure, and likely to compromise reliability.

Different "Top Tier" brands often have good additive packages that are specific to their products. Techron is absolutely good stuff, Shell's V-Power package is pretty good too.
Given price wars between stations it's usually possible to find the good stuff of the same Octane rating within a few cents of ghetto no-brand stations.


2015 Volvo S60 2.0L 4-Cyl

Actually, the sulfur stink was coming through the AC vents more than from outside....

Fuel was from Kroger... we had a bunch of points ($1/gal discount) and filled up wifes car (requires premium) and mine from the same pump. Never had a problem with their gas previously, but, there's always a first time.

Kroger, Costco, et al tend to get the cheapest bottom rack fuels to sell in bulk, and depend on blending it to meet minimum specs. But it depends on your regional fuel distribution companies and their shenanigans for the most part. Sometimes those Krogers and Costcos are filled from the same trucks that fill the storage tanks at Chevron and Shell stations, sometimes they're filled up from the stuff just barely better than what the no-name stations buy. The contracts those stations have with those specific distributors will usually dictate fuel specs and standards.

If your wife's car didn't have any issues, I'm suspecting that something might be off with your S40, and it wasn't the fuel that was bad or wrong.

Edit: Just read the TopTier page and that's for the 'Top Tier' rated detergent package in combination with not using effective octane boosters like MMT. Doesn't actually mean the fuel itself is 'Top Teir' just that the fuels they sell have additive packages with detergents that meet those program standards.

[DMCutter]

I run a 19 psi map on my hopped up WRX and even with meth injection I wouldn't think of running lower than 91 octane. I used to have a Boxster S and bitched to my mechanic about the cost of Pilot Sports. He said tires are a consumable and you have to pay to play. Same with gas. I know a gal with a Macan S who doesn't want to pay for premium and doesn't care about degraded performance...scratching my head about why she bought that car.

[DDTSGM]

Same reason I ran mid-grade in my 5.7L Hemi equipped Ram.

I also used mid-grade in my 5.7 Ram. Then one day while returning from a trip I ran low and stopped at a station that didn't have mid-grade so filled up with 87 octane. Didn't notice anything so continued using 87 octane. It's been at least an oil change now, and my mileage hasn't seemed to suffer and performance in towing my trailer or pontoon seems the same. Of course, Kansas doesn't have mountains, so there is that.

Next year we'll be trailering Route 66 from Baxter Spring KS to Needles so we'll see how it does in up and down. I'll be prepared to switch back if needed.

With my 2003 Ram's 4.7 I noted that I got a little over 2 mpg better using ETOH free while towing our enclosed cargo trailer to races. Since I was always traveling in an area where anyplace I could use my fuel points didn't sell ETOH free, it didn't make economic sense to use the better gas.

[HeavyDuty]

My 2000 Impala with 3800 got better mileage and performance with mid grade 89 - and was a lot more fun. Price per mile was almost a wash.

[BehindBlueI's]

I also used mid-grade in my 5.7 Ram. Then one day while returning from a trip I ran low and stopped at a station that didn't have mid-grade so filled up with 87 octane. Didn't notice anything so continued using 87 octane. It's been at least an oil change now, and my mileage hasn't seemed to suffer and performance in towing my trailer or pontoon seems the same. Of course, Kansas doesn't have mountains, so there is that.

Next year we'll be trailering Route 66 from Baxter Spring KS to Needles so we'll see how it does in up and down. I'll be prepared to switch back if needed.

With my 2003 Ram's 4.7 I noted that I got a little over 2 mpg better using ETOH free while towing our enclosed cargo trailer to races. Since I was always traveling in an area where anyplace I could use my fuel points didn't sell ETOH free, it didn't make economic sense to use the better gas.

Lower elevations and cold will help for sure. There's a *lengthy* thread on Ramforum where a guy drove with various grades of gasoline with real time data logging and the truck pulled timing even at 55mph. See: https://www.ramforum.com/threads/anyone-switched-to-87-octane.189630/page-35#post-2709541