Cheap math on supposed longevity benefits of premium vs. regular

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If your engine doesn't need high octane or have a preignition issue, I doubt using high test will yield any benefits.

You're right to a certain point. If your engine cannot alter its timing to make the most of the increased octane, then you won't see additional power. However, most premium fuels have increased levels of detergents that should keep things cleaner.
 
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You're right to a certain point. If your engine cannot alter its timing to make the most of the increased octane, then you won't see additional power. However, most premium fuels have increased levels of detergents that should keep things cleaner.

Nope. The additive content is no different between regular and premium of the same brand/station. It all gets blended at the same ratio going in the storage tanks per that brand's spec.

The only difference is the auto-ignition point of the end gases. That's it, nothing else.
 
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That was not true and I highly doubt it has changed .

There was a detailed testing years ago proving beyond any doubt that Exxon, Shell and BP all had much higher additives in their 93 vs 87....

The following is just from my memory of what that testing showed.... And that has been 3+ years since I have looked up that testing.

Aka Exxon regular 87 had like 18 ppm additive content per 100 mL.

And Exxon Supreme 93 was near 31 ppm additive content per 100 mL

Shell regular 87 was near 20 ppm additive content per 100 mL.

Shell Premium 93 had 34 ppm additive content per 100mL.

And the hoopty Doo gasoline like Speedway, Pilot etc was like 8- 10 ppm per 100 mL for their regular 87.

There was a darn table of both regular vs premium of the same brands tested....

I can't find it but it has been posted on here before. And it was quite clear the additive content was most certainly much higher with 93 vs 97.


Has that changed ?

Maybe.

But I kind of doubt it.
 
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Nope. The additive content is no different between regular and premium of the same brand/station. It all gets blended at the same ratio going in the storage tanks per that brand's spec.

The only difference is the auto-ignition point of the end gases. That's it, nothing else.

Maybe the US is different to the UK then. In the UK, all garages who sell a premium fuel advertise increased detergency levels among other things.
 
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Most gas stations sell very little premium. It's more likely to be contaminated or stale.
Bingo.

It may also include more ethanol. It won't exceed 10%, but refiners are allocated how much ethanol they must use in gallons per year, not in percentages - which is why the pump says it may have "up to 10% ethanol". Ethanol is an octane booster. Cheapest way to boost your octane is add the 10% to the premium, use up your leftover allotment to the regular, whatever that end up at.
Ehh. Not entirely sure this is accurate. In suburban areas (Chicagoland at least) a fair amount of premium is used. Less than regular, but I wouldn't say it's "very little". Regarding ethanol percentage, when I step over the border into WI most of the stations I frequent post that their premium doesn't contain any ethanol. Perhaps WI is an oddity, but that's what I'm currently seeing.
 
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when I step over the border into WI most of the stations I frequent post that their premium doesn't contain any ethanol. Perhaps WI is an oddity, but that's what I'm currently seeing.

Over the border in WI there isn't an oxygenated gas requirement like there is in suburban Chicagoland, which by the way has had mandatory emissions testing since the mid 1980s. So they can sell ethanol free gas.

(Areas that have mandatory emissions tests usually also have an oxygenated gas mandate).

It's the same reason why the nearest gas station that sells ethanol free is 20 miles from where I live.
 
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Ehh. Not entirely sure this is accurate. In suburban areas (Chicagoland at least) a fair amount of premium is used. Less than regular, but I wouldn't say it's "very little". Regarding ethanol percentage, when I step over the border into WI most of the stations I frequent post that their premium doesn't contain any ethanol. Perhaps WI is an oddity, but that's what I'm currently seeing.
I said it may include more. Around here if you want ethanol free you pay a buck a gallon more and its still listed as 87.

Refiners are told they need to use a certain amount of ethanol. This year it was 15 billion something or others - gallons, barrels, can't remember. There was a big hub bub about it because the EPA retroactively lowered the required amount for 2020 and 2021, because the refiners couldn't use enough because they didn't sell enough gas, so if the EPA had not the refiners would have been fined. The green crowd was not happy.
 
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I think it used to be that way in the US prior to Top Tier coming on the scene. Higher detergent content is for the Top Tier fuels and is the same across all grades. That's per reps at Sunoco and Chevron when I inquired a couple years ago. My uncle, who's worked at the Chevron refinery on the gulf coast for 42 years, stated the same that regular and premium get the same detergent content. Maybe Shell and others do things differently?

If I'm wrong about this, I would like to know, so I'm going to do some digging this morning.
 

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I think it used to be that way in the US prior to Top Tier coming on the scene. Higher detergent content is for the Top Tier fuels and is the same across all grades. That's per reps at Sunoco and Chevron when I inquired a couple years ago. My uncle, who's worked at the Chevron refinery on the gulf coast for 42 years, stated the same that regular and premium get the same detergent content. Maybe Shell and others do things differently?

If I'm wrong about this, I would like to know, so I'm going to do some digging this morning.
AFAIK, Top Tier is mainly a performance spec, not so much additive content spec. I don't think they care about detergent content so much as detergency and deposit control.

Also, like oil specs, it's a minimum standard, which leaves plenty of room for one grade to outperform another. They all have to be at or above the minimum, but they can theoretically exceed it by different margins.
 
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Premium being more refined makes no sense. There's nothing of the sort. Nor is there any difference in "purity" which makes no sense either. The octane rating, which is actually an anti-knock index in the US, is nothing more than a measure of the fuel's resistance to auto-ignition of the end gases. That's it. It doesn't represent purity, refinement, or other quality parameters. It doesn't change the burn rate, laminar flame speed, vaporization, air/fuel homogenization, air/fuel ratio, engine temp, piston/chamber deposits, etc... None of that.

Gasoline is a cocktail of many different feedstocks blended in different ratios to achieve a target octane rating or other property. Premium will tend to have more aromatic content as aromatics usually have a higher octane rating. Increasing that concentration 5-10% and adjusting some lower octane (but still high BP) alkenes, alkenes, and olefins to balance out the formula gives the higher final octane rating.

Those feedstocks change almost every batch as well. Pump gas is made with the cheapest stocks they can get at the time and batches can vary wildly to meet a price point.

Sadly, what's written in magazine articles and even Sunoco's "tech" page isn't written by engineers or blenders. It's written by marketing desk jockeys, phrasing stuff passed to them in their own over simplified interpretation of a very complex subject. They get stuff wrong more often than right when it comes to fuels. (and lubes)
I found this on the EIA website.
4EC61994-4420-46F6-927B-FD899AEF225A.jpg
 
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I used to work with a guy that burned Premium in his Toyota truck with the 22R 4 cylinder engine . He said it was to make his truck last longer . Whatever that meant . He gave the truck to his teenage son who trashed it in less than two years .
 

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Nope. The additive content is no different between regular and premium of the same brand/station. It all gets blended at the same ratio going in the storage tanks per that brand's spec.

The only difference is the auto-ignition point of the end gases. That's it, nothing else.
IIRC, both Petro-Canada and Shell claim their premium fuels do have higher levels of additives.
 
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Was chatting with a shop owner who prefers premium gas even in cars that don't require it. This is not only because of knock resistance and fuel economy, but also because it has a lower level of impurities. Taking that for granted, and given the value of cleanliness in an engine, this makes some sense in the abstract. Though, whether this would make premium worth the money is another matter.

This all got me thinking. I can't assess the point about cleanliness, but I can do some back-of-the-envelope math to see if there's any chance a longevity benefit could pan out, regardless of how regular and premium differ.

If the only reason you clicked was to get mad at what you thought the answer would be, I'll save you the trouble: For engines that don't require premium, the most likely answer is no. At least, not according to what I found.


Caveats before you read further:

1. Nothing below says anything definitive whatsoever. This model is not another "index" or any of that junk. It's a crude thought experiment with some simple math. In some cases it might – might – yield inferences good enough for making practical decisions, which is all I wanted from it. In other cases it might yield some entertainingly weird results. Please, please don't pretend there's anything more to it than that.

2. This does not apply to engines that require premium gas.


The way I approached it was basically to compare per-mile costs of fuel and engine rebuilds for regular and premium gas. The math had several steps, but it's all basic:


1. [price per gallon of fuel] ÷ [mpg with that fuel] = [per-mile cost of that fuel]

For regular gas, I just filled in current numbers. For premium, I used the current price and generously assumed an mpg increase.


2. [cost of engine rebuild] ÷ [engine rebuild interval] = [per-mile cost of engine rebuild]

For regular gas, I made assumptions based on people's typical experiences. For premium, I kept the same number for engine rebuild cost but left the rebuild interval as an unknown.


3. [per-mile cost of regular] + [per-mile cost of engine rebuild w/ regular] = [per-mile cost of premium] + [per-mile cost of engine rebuild w/ premium]


4. Because each of the terms above is a fraction, the equation can be rearranged to isolate the unknown – i.e., the engine rebuild interval with premium:

View attachment 118061

Plugging in numbers on the left side of that equation and solving it should yield the minimum rebuild interval necessary to break even with premium gas. The engine would have to last at least that long for premium gas to be worth the money over regular.


I made a spreadsheet with all of this and threw in some numbers to play around. Here are some example outcomes:

View attachment 118016
Here, the model suggests the engine would have to last >2x as long on premium than on regular for the fuel price to be worth it. Not a chance in heck of that happening.

More:
View attachment 118052
View attachment 118053
Even more ludicrous numbers. I'm sure most of us are on the same page about this but the numbers really drive the point home IMO.

View attachment 118055
See that negative sign here? That means the model suggests premium gas wouldn't be worth using in that scenario even if it made the engine last literally forever. In other words, given these numbers, it'd be cheaper to run regular and rebuild the engine when it dies than to run premium and have the engine be immortal.


I also tried plugging in numbers like what I've seen at sketchy no-name stations vs. Top Tier stations around here:
View attachment 118057
Awkward. 😬

Not actually worried by that last one. The model doesn't properly account for the elevated risk of a truly bad batch of gas from a sketchy station, which IMO is enough of a reason to write off sketchy gas and render the comparison moot.

Something else this doesn't account for: the fact that, the longer the engine runs, the higher the probability that it'll encounter a bad batch of gas or some other catastrophic event that'll cut its life short. That makes those long rebuild interval estimates even more hideously unlikely.

So, again, nothing definitive, but... seems safe to say any supposed benefits of premium gas in a car that doesn't require it are sketchy at best.

What do y'all think?
While you make a sensible argument, I have a different perspective. So, gas in SoCal runs around $5.50/gal, which is my Costco price. The difference between 91 and 89 is around .15 cents, or 2.7%. So worst case it will cost me an extra $1.60 or so to fill up, good for 450-500 miles. I believe that the octane boost allows higher operating efficiency. And considering other operating costs, air/oil filters, oil changes etc etc, this is lost in the wash, worst case, best case I will easily get 2.7% better gas mileage. And since I have a Kia and everybody knows it will grenade at any moment, well .......
 
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While you make a sensible argument, I have a different perspective. So, gas in SoCal runs around $5.50/gal, which is my Costco price. The difference between 91 and 89 is around .15 cents, or 2.7%. So worst case it will cost me an extra $1.60 or so to fill up, good for 450-500 miles. I believe that the octane boost allows higher operating efficiency. And considering other operating costs, air/oil filters, oil changes etc etc, this is lost in the wash, worst case, best case I will easily get 2.7% better gas mileage. And since I have a Kia and everybody knows it will grenade at any moment, well .......
Yeah, if our premium was only 3-4-5% that regular, I would probably run it in the Outback atleast. It runs at low rpms a lot and probably on the edge of knocking most of the time.
Typically stations here totally overcharge for 91 vs 87 though, so for the 15-20% in price increase I only run premium in stuff that needs it.
 
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Canada, eh?
Most gas stations sell very little premium. It's more likely to be contaminated or stale.
Depends where you live and the median (average) income of those who fill at those stations.
A fuel station in a predominantly affluent neighborhood will sell comparable amounts of premium and regular.
 
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