87 Octane "or Higher"

[CupidinChicago]

My Hybrid Friends- I just bought a 2014 Toyota Avalon Hybrid and the manual says the car can run on 87 octaine or higher. I find it comical how the engineers do not elaborate on this statement? If I use a higher octaine what will happen? Will I get better mileage, cleaner engine, better acceleration?

[FROSTYBALLS]

Here in the UK, we have a different octane rating (RON) to the US (Anti Knock Index or Pump Octane Number). The two aren't directly comparable, but the US octane numbers are generally 4-5 lower than those in the UK.

Unleaded petrol in the UK has to be a minimum octane of 95 RON, and super unleaded (the higher octane choice) has to be a minimum of 97 RON - supposedly equivalent to 90-91 and 92-93 in the US. Shell and Tesco (one of our supermarkets) currently offer 99 RON octane fuels, and BP a 98 RON (BP did offer a 102 RON).

In the UK the higher octane (super unleaded) fuels are sold as having better detergents (thus a cleaner engine) than unleaded, and are also sold on the premise of better mpg/better responsiveness. Also the branded petrol (Shell, BP, Esso, Texaco, etc) supposedly have better detergents and additives than supermarket branded petrols.

Moved to the Hybrid/Toyota Prius club (with a link left in Toyota Family).

[Cyker]

It's just the usual benefits of having higher octane I guess, but TBH the hybrids don't worry as much about the fuel as the leccy motor provides the lion's share of the torque.

From what I've read from HSD owners here the octane doesn't really affect the performance or efficiency of the car significantly, but that's going from 95 RON to 99 RON...

[Joseph D]

... Will I get better mileage, cleaner engine, better acceleration?

I can't speak to the cleaner engine, because that depends on the detergent packages of the different grades. Although they push the higher octane fuels as having "better" cleaning power, there are still detergents in the lower octane fuel. In some states, detergents are mandatory. All this hoo-haa is purely marketing hype. And from some of the rubbish (sometimes quite passionate) I've read in opinion pieces around the place, I'd say the PR people have quite some success.

I can speak to "better millage?"; "better acceleration?" In a word No. I did some testing of this personally and found that higher RON/PON ratings did not provide any advantage for either, and, in the case of fuel economy found that higher RON fuel did not provide any better FE and on two tanks actually worse - not by a big amount, but worse none the less. Science also supports these observations.

Technically, using a higher rated fuel will not harm your car, using a lower rated fuel WILL. Do not two this. Lower octane WILL damage your IC engine.

If you wish to verify my conclusions for yourself, you must record all your fuel ups meticulously as relying on your memory will catch you out. I know this as I was forming the impression that using the higher RON fuels was improving my fuel economy - UNTIL i reviewed my Fuelly records. This showed quite categorically that I was mistaken.

So, in a nutshell, save your money and use the fuel as recommended in your owner's manual 87PON in the US and 95RON in the UK.

FYI, the "or higher" is there for the case where you find that the recommended fuel is not available and you HAVE to fill up now. Then you have the choice of higher or lower. In this case, the only choice is use higher as it will not damage your ICE.

I hope this helps.

[Sagitar]

There is no benefit in running higher Octane fuel unless you are running an engine with a higher compression ratio.

There is no extra energy in higher Octane fuel. Octane is a rating of how well the fuel resists ignition due to compression. If you run low Octane fuel in a high compression engine the fuel will ignite prematurely and cause damage. A high Octane fuel lets an engine designer use a higher compression ratio and that is all. The amount of energy in the fuel is pretty much the same and may actually be slightly lower in high Octane fuel. The extra engine power comes from the higher compression ratio, not from the specific energy of the fuel. Using higher Octane rated fuel in a lower compression ratio engine may well increase fuel consumption.

The Octane rating specified by the manufacturer is the rating required for the engine to run without pre-ignition. Anything higher is just a waste of money. The "or higher" note in the manufacturers spec is simply telling you that if the specific rating is not available, it will do no harm (apart from the pain in the pocket) to put in fuel with a higher rating.

[Cyker]

Well some cars can change the ignition timing if they sense you've put higher octane fuel in, which can give improved performance and fuel economy, but this only tends to be the case in more expensive performance cars, usually things with turbos in them

I'm not sure if the HSD's IC engine can do that, but I suspect not as it doesn't drive the wheels directly so any performance lag from the IC can be compensated for by the electric motor.

But yeah, just do what is says and use 87RON or better in your case - Anything less may cause 'knocking' or pre-detonation which can damage the engine. Anything more will just cost you more money but for little to no other benefit.

[Grumpy Cabbie]

To add confusion to this, don't they recommend lower octane fuel in America if you live at altutude? I guess the high parts up in the mountains like Colorado or similar.

But as the largest mountain in the UK is probably a hill to them, we don't need to worry about such things :)

[Cyker]

Oh man, that must be a PITA if you fuel up with 95 at the bottom and then have trouble at the top, then change to 82 at the top and then your engine blows up from pre-ignition when you get back down again

[Grumpy Cabbie]

Oh man, that must be a PITA if you fuel up with 95 at the bottom and then have trouble at the top, then change to 82 at the top and then your engine blows up from pre-ignition when you get back down again

But if the entire few hundred square miles are 5,000 feet above sea level, then you have an issue.

Your humour caused me to google the issue and I found the following;

http://mechanics.stackexchange.com/questions/6920/can-i-use-lower-octane-fuel-at-high-elevation

So I was right lol

[kithmo]

Most EFI petrol engined cars, from the mid 90s on (not just high performance cars) have the facility to !Removed! the ignition timing electronically if knocking is detected, via signals from the knock sensor. The timing is electronically set to maximum advance by the ECU and retarded until no knocking is sensed. This means lower than recommended octane fuel could be used but will just cause the engine to perform poorly. I doubt it would harm the engine unless the fuel is extremely poor quality or contaminated.

[Joseph D]

Well some cars can change the ignition timing if they sense you've put higher octane fuel in, which can give improved performance and fuel economy, but this only tends to be the case in more expensive performance cars, usually things with turbos in them ...

The "some cars" to which you refer, are cars which have high(er) compression engines and so, by definition, have to use higher octane fuel. Yes, you are correct that modern variants of these cars do have anti-knock sensors and you are also correct that the computers can adjust the timing if they detect knocking, to protect the engine from damage. However, you are incorrect in your assumption that the computers will re-tune the engine to "give improved performance and fuel economy". The computer de-tunes the engine upon detecting knocking, thereby saving the engine from damage, but this de-tuning will almost certainly give poorer performance and poorer fuel economy. The actual case is this, the the engine is tuned for the correct fuel, and if knocking is detected, it will de-tune. It is not capable of detecting higher octane, and so it is not even possible to do as you say.

... I'm not sure if the HSD's IC engine can do that, but I suspect not as it doesn't drive the wheels directly so any performance lag from the IC can be compensated for by the electric motor. ...

The HSD is a modern system so, yes it can do this. However, since it is designed to run on RON95/PON87, it will get very little opportunity to do this. Maybe high in the mountains of Colorado.

As seems to be your usual habit , your comments are off point and an irrelevant tangent to the discussion.

Thinking out loud, maybe. Please stop doing this.

[Cyker]

You say that, but we have plenty of VVTi people here who reckon their cars, while designed to run on standard 95 premium, have been able to take advantage of higher octane fuel and have both felt it's given better performance, and measured better mpg.

[Joseph D]

You say that, but we have plenty of VVTi people here who reckon their cars, while designed to run on standard 95 premium, have been able to take advantage of higher octane fuel and have both felt it's given better performance, and measured better mpg.

I can't comment on said unspecified claims, and it would be better for said people to make their claims themselves and back it up with some objective evidence rather than a third person citing hearsay.

But .. "have both felt it's given better performance" doesn't sound objective. If they "measured better mpg", then why the subjective "feelings"?

Like I said before, the PR marketing machine is a powerful thing and I have heard some impressionable people make passionate statements. Just because you're passionate doesn't make you right.

I am not convinced, sorry.

[Cyker]

While you can measure mpg directly, performance tends to be a bit more subjective for those of us that don't have access to a dyno!

IIRC I got into a similar argument over the V-Power diesel some years back: Some people felt it made no difference but some people, including myself could hear the engine was running with less of the clatter that you get with diesel engines and had altered performance characteristics. I could measure the mpg differences, but without a dyno or a way of measuring smoothness I could only state my observations with no empirical proof.

TBH I was previously on the 'super fuels are a waste of money on non-turbo'd cars' side of the fence, but it was pointed out to me that knock sensors can allow engines to optimise themselves for the fuel that's put in them, although if a car is designed for 95 I'm not sure how much leeway there is. From what grumpy says, I guess there'd be more scope for leveraging higher octanes improvement at lower altitude and in winter than higher up in the summer?

[Joseph D]

IIRC I got into a similar argument over the V-Power diesel some years back

And this is exactly the tangental red herring I'm talking about. Diesel is not petrol. Diesel and petrol behave differently and diesel engines operate differently to petrol engines. There is no co-relation in this context of one to the other.

TBH I was previously on the 'super fuels are a waste of money on non-turbo'd cars' side of the fence, but it was pointed out to me that knock sensors can allow engines to optimise themselves for the fuel that's put in them, although if a car is designed for 95 I'm not sure how much leeway there is. From what grumpy says, I guess there'd be more scope for leveraging higher octanes improvement at lower altitude and in winter than higher up in the summer?

You should have stuck to your guns, you were closer to the money when you held that opinion but, I think you miss understood what you were told, or the person doing the telling (if they did indeed say that) was mis-informed.

Knock sensors detect knocking, pure and simple. If knocking is detected, the engine is de-tuned until there is no more knocking. They cannot "allow engines to optimise themselves for the fuel put in them" and anyone that tells they can, doesn't know what they are talking about or are having a laugh. This is about compression ratios -- an engine cannot reconfigure itself to have a higher compression ratio.

I don't want to keep arguing this point with you, go back and re-read the posts by Sagitar and Kithmo and try and understand the basic principle they are stating. I think we three are on the same page. This is not a matter of opinion, it is simple physics and chemistry.

[Sagitar]

There is little that I can add to my initial contribution. For those who find it hard to believe what I said, then I suggest some Googling. Wikipedia is a good place to start. Here is a quote from a Wikipedia page on the subject:

"A common misconception is that power output or fuel efficiency can be improved by burning fuel of higher octane than that specified by the engine manufacturer. The power output of an engine depends in part on the energy density of the fuel being burnt. Fuels of different octane ratings may have similar densities, but because switching to a higher octane fuel does not add more hydrocarbon content or oxygen, the engine cannot develop more power".

The Atkinson cycle used in the Prius makes it less prone to knocking than an equivalent Otto cycle engine so I would argue that there is even less justification for wasting money on higher Octane fuel.

[Grumpy Cabbie]

My Prius runs sweeter on Shell V Power. Not sure if it is more economical but it's certainly a lot smoother. I wonder if it's just because it's a nicer fuel with more cleaners and stuff in it?

I have a full Toyota service history so obviously the car has been maintained correctly!?! lol, but having always used Asda 95 unleaded and having had to replace a totally gummed up EGR valve at 75,000 miles, I wonder if 95 unleaded is now just nasty?

It isn't just me though, Mrs Cabbie today said she had to put V Power in because of queues and was amazed at how smooth and quciker her IQ was. If she notices, then there must be an improvement.

[Ancient Nerd]

I suspect that it is not so much that the higher octane rating of V-power is the reason for smoother running, so much as it is a fuel that has better additives than the basic supermarket unleaded.

I think you will find that the regular Shell fuel will also give a similar improvement, without the extra cost.

Shell used to keep a significant number of test engines on test beds at their Thornton Research Centre (recently closed down, but I think the work continues in the remaining five centres). These were run 24/7 to test oils and fuels under various simulated driving conditions. The engines were stripped down and checked for wear at intervals. Total mileages were massive.

It is quite probable that other oil companies do the same, but I am quite sure that Asda, Tesco etc don't.

The result is that I use Shell fuel when I can, Esso, Texaco, Total etc if not, and Tesco once a month for the accumulated discount.

[Cyker]

Maybe, but from what other's have said here the Shell normal fuels usually have a much smaller difference than their super fuels so there must still be something else at work there...?

It's been quite hard to quantify as some people say they don't notice any difference and some do! But you can't know if the people that think there is a difference do because of a placebo effect, or if the ones that don't think there is have an issue with their car or are just very insensitive to the performance of their car (e.g. I can feel the change in performance on mine between a warm day and a cold day but a lot of people can't.)

I know when I've tried the Shell FuelSave diesel, I didn't really notice any significant difference from the Sainsburys diesel I normally use. Might be different with petrol, but I suspect not...

(On a slight tangent, I did try a bunch of different diesels a while back as kind of a half-assed experiment. Totally unscientific, but IIRC the smoothest were Shell V-Power and Morrisons (!!), roughest was Esso and Tesco! )

[kithmo]

I think the perception of smoother running and more power is probably because the higher octane fuels allow the engine to run at its best all the time.

I can't remember where I read it, but another marketing ploy was that it usually takes about 3 consecutive tankfuls of the higher octane fuel to clear any trace of the previous previous fuel used, as (apparently) mixing two different octane ratings will always bring the octane level down to the lower rating. This was obviously to make you buy 3 tankfuls of the more expensive stuff before you gave up.

[Joseph D]

My Prius runs sweeter on Shell V Power. Not sure if it is more economical but it's certainly a lot smoother. I wonder if it's just because it's a nicer fuel with more cleaners and stuff in it?

Why don't you try 4 tanks full of Fuelsaver 95 and see for yourself? You just might be able to save a few quid per tank. ;) I ran my Prius exclusively on Fuelsaver 95 after trying V-Power and noticed no real difference in performance. I thought maybe I was getting better economy on V-Power (placebo effect) until I checked my Fuelly records, so have been saving my money ever since, One thing though, you might get a benefit if the detergent package in V-Power has something that the Fuelsave detergent package doesn't and if that is the case running the odd tank now and then might give a benefit by way of cleaning the engine. Who knows? All I know is my car ran great on Fuelsave, saved a few bob and got excellent economy.

I have a full Toyota service history so obviously the car has been maintained correctly!?! lol, but having always used Asda 95 unleaded and having had to replace a totally gummed up EGR valve at 75,000 miles, I wonder if 95 unleaded is now just nasty?

Different brands, brand vs supermarket now there's a opinion minified. Let's not start re-hashing that old chestnut. Yes, anyone can have an opinion on that subject and it doesn't matter. Each to their own. live and let live.

It isn't just me though, Mrs Cabbie today said she had to put V Power in because of queues and was amazed at how smooth and quciker her IQ was. If she notices, then there must be an improvement.

I'd be bold as to say it is most likely the placebo effect where in your mind you need to justify the extra expense, so become focused on performance and start noticing things that were already there. It might be detergents. Maybe she tanked up on the change over to summer fuel formula. Maybe it was warmer out. So many factors. Who knows?

[RunningInPleasePass]

Always try and use Shell regular myself so unable to comment on different fuels, but the weather certainly makes a difference, the warmer the weather the better MPG, and the car runs smoother as well, I envy anybody who lives in a warm climate!

[Cyker]

Each season has its pros and cons; I like winter too as, once the engine's warmed up, you can feel the extra pull thanks to the denser air; It's like having an extra intercooler :D

This winter was a bit too mild down here for it to really be noticeable tho :( It never even really dropped to winter-tyre temps :(

[johalareewi]

you can feel the extra pull thanks to the denser air;

Denser air increases air resistance though :(

[Cyker]

This is also true :(

Thankfully, at the speeds I tend to drive at that rarely becomes a major issue (Although I have noticed my foot has been getting heavier these past few years )