I was always told to buy 98 because you get more K’s out if it and it’s better for your engine??? But I always choose the cheapest fuel because I drive a Toyota corolla and don’t really care about my car.
Though the thing is (I learned from my little test) that the cheapest fuel isn’t actually the cheapest fuel, because you have to fill up more often. Therefore it actually costs you more because the savings you make directly at the pump aren’t in proportion with the efficiency of the fuel.
I found the the 95 lasted me a day or two extra than the 91, so it would be an actual saving of around $80 a year. I’ll have to see if it’s even better with 98.
I’m mostly annoyed I was being duped at the pump for so long! What’s cheap often isn’t really cheaper… And it’s not even like 91 has any added bonuses (like being better for the environment).
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Oh I did this same test awhile back after having the same question! I drove the same trip from the Blue Mountains to Sydney several times a week. The e10 usually got me about 500kms a tank, the 95 about 550kms and the 98 550kms.
Ever since I’ve just been buying the 95 as it seemed to be the best value for money.
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It really depends on the engine tune and/or engine management system as to whether a higher octane fuel is beneficial. The Research Octane Number (RON) represents a level of resistance to self-igniting from the heat of compression in the combustion chamber after the spark plug has fired but before the flame front has reached this part of the combustion chamber. This is very destructive process known as detonation, knocking, pinging, and several other names. It is noticeable as a rattling sound under high load, generally most distinctive at low engine speed, such as accelerating in too high a gear, and well be worse in hot weather. The noises are shockwaves from the detonations, and they cause massive stresses on the engine.
Engines with high compression ratios or forced induction require higher octane fuel because they have higher cylinder pressures and temperatures. You should not use a lower RON fuel than recommended. Higher RON fuel can withstand higher temperature and pressure without igniting, but it also burns slower. You can use higher RON fuel than recommended, but the ignition timing usually needs to be advanced to allow more time for the fuel to burn completely. Many modern cars with high performance engines, particularly those with forced induction, have knock sensors that continually monitor the engine for detonation, and retard the timing to cool the cylinders by not completely burning the fuel if detonation is detected. This can be subtle or savage, depending on the engine management system programming.
The higher octane fuels have been marketed as a premium product, so they have a number of other features. They are denser, which provides a degree of protection against high cylinder temperatures by enriching the air/fuel ratio. This also lets them make more power, or to travel further on a tank. They also have higher levels of detergents to dissolve wax deposits in the injectors and carbon buildup on the inlet valves. Carbon buildup can cause hot spots that contribute to detonation. Finally, they also have tighter tolerances on sulphur contamination, allowing them to be marketed as environmentally friendly.
In summary, using a higher octane fuel than specified could be beneficial, but it depends on your engine and it’s state of tune/engine management. I personally use 98 octane fuel, but my engine detonates on 91 RON since the head was machined flat (reducing the combustion chamber size and increasing the compression ratio) after overheating.
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Was very interested to read on a recent 12 month test between the different octane ratings of fuel . That is 91 , 95 , 98 . It only cost on average $20 more to use 98 Octane for 12 months . It gave no details of the cars used or the compression ratio of the engines involved as that would have a bearing on the outcome of the result .I personally use BP ultimate 98 in my own car as it has a high compression motor .
I tested 91 and 98 fuel types on a 2004 Hyundai Elantra and a 2014 Mazda 3, both worked out cheaper to run on the 98 due to the extra kilometres achieved per tank. I keep a spreadsheet with litres filled, the price, kilometres achieved per tank.
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I’m so glad everyone on here was as nerdy as me about this!
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From what I’ve read in motoring magazines there is no need to use a higher RON rating than that recommended by the automobile manufacturer. However, if you use a lower rated fuel you risk seriously damaging your motor.
Using a higher rate fuel won’t increase performance or economy and probably won’t improve performance - except were the manufacturer has provided advises differently.
I have queried Holden regarding my 3.8 litre Statesman regarding this and they replied that although using a higher rated fuel will not damage the motor, it won’t provide any extra benefits.
So, if you fill up with 98 RON fuel in a motor designed for 91 RON you won’t harm it, but you will pay more and the petrol company will benefit. I am also informed that the suggestion that your motor will be cleaned by higher rated fuel is a furphy. With electronic engine management and fuel injection the modern motor does not carbon up. modern fuel filters keep injectors clean and the injector cleansing Powers of higher rated fuel is overrated.
Welcome to All.
I live in FNQ and drive a Nissan X/Trail 2007, the wife drives a Mitsubishi 380, 2004 model.
Up in these neck of the woods, Premium fuel is sold at a premium price up to 10c/L more.
I gave up working out if there was any benefit between the octane ratings. In any case I add Morleys Upper Cylinder Lubricant (1ml /L) to all the fuel I use … in 2 cars, ride-on mower, brush cutters, generator, chain saws, etc., etc…
Both my cars get serviced once a year only … why go for an over-kill?
All my equipment, petrol driven, have worked without a hiccup for many a year. So if anyone is concerned about saving small cents worth, my suggestion is sell your car and use public transport. It takes longer, is not as convenient, but hell, look at the cost savings viz. insurance, registration, maintenance, wear & tear, depreciation, the list goes on and on.
Well anyway that’s my 2-bobs worth. Happy driving and keep the government coffers full.
Cheers
David Knox, J.P.
20-10-2016
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Buying a fuel that exceeds the manufacturer’s RON recommendation is a complete waste of money. Take it from an expert engineer.
I am of the view everybody who is of the view that high octane fuel is worthwhile improvement in their vehicle should use it, that way they will increase the refined volumes that should put downward pressure on its price, lowering the differential between it and regular fuel.
That will have the happy byproduct of helping us classic car drivers who must use it.
I would like to think that was the case, but evidence to date suggests the vendors are increasing their spread from 91 to 98 as more vehicles need 98. In Victoria, although not everywhere, they are able to do this under the radar because they do not need to put 95 and 98 prices on their signage, only on the bowsers. Since the 91 prices are generally in lock step people wrongly expect the 91 and 98 to also be in lock step so many if not most motorists don’t pay attention.
Our Shells have increased their 91-98 spread to $0.20 while most others are still at $0.18; they used to be $0.16, and before that $0.12, if that makes the point.
By ‘modern engines’, do you mean fuel-injected engines? E.g., would the block in the front of a '96 Micra include these modern installations?
Knock sensors have been around for a while and they use certainly predates 1996 but on older cars they were not fitted to all engine designs even if the car had electronic fuel injection, they were used only on engine designs that had a tendency to detonate.
I recently saw a 2002 vehicle that did not have a knock sensor and it was safe to assume that engine design was naturally resistant to detonation.
If you cannot determine it by checking with the maker then have a look in the engine specs, for these look in the owners handbook and check the Compression ratio.
The vehicles Comp ratio will likely hold some clues, if it is around 9.5:1 or above it is highly likely does have a knock sensor, if it is around 9.2:1 and below if may not.
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Expect an appeal but ‘Man successfully sues Mitsubishi for ‘misleading’ fuel label’:
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About time there was some action taken against the dodgy claims made by car manufacturers regarding fuel consumption,
What point is there in manufacturers quoting supposed consumption achieved in laboratory testing that cannot be replicated by consumers except when coasting downhill?
Our MY15 Honda CR-V was rated at 8.7L/100km and it achieves around 8L/100km on long runs and around 10L/100kn around town.
It is hard to believe a much heavier ute could be rated for the fuel consumption figures quoted in the article in The Age.
It appears to be just another shonky Mitsubishi episode.
I recall an episode on TV a decade or so ago when people in Japan were being killed by the wheels detaching from Mitsubishi trucks and Mitsubishi denying there was any problem.
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Ah! It’s a diesel if that is what the DID in the
Mitsubishi 2016 Triton GLS DID Auto DC-PU model description means?
P.S. approx 2,000kg kerb weight vehicle for the current model and 7.9l /100km ADR fuel consumption for the current model It does sound almost too good to be true? But it is a diesel!
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Would it matter what fuel it was (you probably didn’t mean that distinction)? If the label quotes some level of consumption but was shown to be inaccurate if it was less efficient then the claim should be challenged. If it was more efficient we could laud it’s claims but how likely would that be? 
Trouble for these figures is that they have to try to standardise the tests somehow, so what is measured can be related between different vehicles but VW cheated that system so is anything really that safe to treat as kosher?
I guess people do though. They look at cost of running a vehicle and performance and thus may need to look at fuel consumption and thus possibly a choice of engine type. I know I look at cost of fuel to distance achieved and weigh up engine choices partially based on that…more often it is colour though 
Totally agree, unless someone is comparing it with a petrol engined vehicle. 
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It is not the car manufacturers that make dodgy claims … they are justing following the mandated fuel consumption testing regime. It is this regime that needs to change to reflect real driving conditions.
Choice covered this a few years ago…
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