There has been something of a propaganda campaign to try to convince motorists that premium fuel burns cleaner and results in better fuel consumption figures, but is this true?
Premium fuel has a higher octane rating than standard unleaded. Normal unleaded is rated at 91 octane. Depending on where you buy your fuel, you can fill up with 95 octane or ultra-premium at 98 octane.
Of course, we are all susceptible to numbers and inclined to think higher equals better.
The internal combustion engine works on the principle of drawing in fuel and air on the downstroke (intake), squeezing it on the upstroke (compression) and then igniting it (the power stroke), which in turn pushes the piston back down and turns the crankshaft. On the next upstroke, the remaining gases are pushed out of the engine through the exhaust. And that’s why it’s called a ‘four-stroke’ engine.
More powerful
The higher the compression on the upstroke, the more force is generated and applied to the downstroke. That’s why so-called high compression engines are more powerful.
If the remnants of gases from the previous ignition stroke cause the fuel/air mixture to ignite before the piston reaches its highest point in the engine, it’s called a misfire and the noises it produces are known as ‘knock’. The result is a loss of power.
The solution is to retard the explosion, so that it happens at just the right moment. Premium fuel is just as explosive as lower octane fuel, but doesn’t ignite as soon.
91, 95 or 98?
Those old enough to remember will recall that low quality fuel made high compression engines impractical. Way back, those of us using high performance engines had to find and use av (aviation) gas (usually rated at 100 octane) to get the best performance out of our engines. Using a lower octane fuel caused the dreaded ‘knock’, in turn leading to premature engine wear and fouled spark plugs.
Modern cars use a variety of sensors to adjust the engine timing to compensate for different octane ratings. If your owner’s manual recommends 95 or 98 octane fuel, these electronics will usually eliminate knocking if you occasionally have to fill with a lower-than-recommended octane fuel, but doing it consistently isn’t a wise policy.
Premium fuel, as the name implies, costs more than non-premium fuel, and often by a considerable margin. If your car is recommended to run on 91 octane fuel, filling it with premium won’t do any harm, but it will add considerably to your running costs.
Fuel myths
Despite claims you may have heard, premium fuel does not clean your engine. The additives in some fuels are designed to clean older engines but won’t make much difference to cars with modern fuel-injection systems.
Also, you may notice a small improvement in fuel consumption but nowhere near enough to offset the higher cost. You’ll see far better results by adopting economical driving habits, keeping your car tuned and ensuring your tyres are at the recommended pressure.
Paul Murrell is a motoring writer and creator of seniordriveraus.com, which specialises in “car advice for people whose age and IQ are both over 50”. This article first appeared on seniordriveraus.com
Do you make a point of buying premium fuel? Why or why not? Why not share your opinion in the comments section below?
Also read: Experts call for nationwide testing of older drivers
I have BF 2007 model Falcon 4LTR petrol. I currently use 95 fuel because of test results over several years test on each 91 and then on 95 fuel as a comparison. The 95 came out on top even though it cost more per litre to buy, it was cheaper over all because of :
*smoother running engine
* more km per litre.
* significant reduction in the overall running cost of the vehicle
I only use premium fuel for my garden equipment, lawn mower and chainsaw. It seems to last much longer, whilst ordinary fuel soon clogs up the carburetor needing an expensive visit to the repair shop. It works out cheaper than using so called fuel conditioners which achieve the outcome.
Thanks for the review and comments.
Does this apply to diesel engines as well?
Buy a diesel and you only have 1 choice
Actually no, many service stations do sell a “Premium” or “V-Power” claiming more stable performance and better economy. Not being a diesel user, I do not pay attention beyond that. A friend with a diesel and high kilometres only uses the Premium and so cannot give me a comparison.
I have had 2 diesels for many years you only have one choice but some say there are two l always fill up from what ever diesel bowser is available
Every one reading this has the ability to create a spreadsheet to compare the relative differences between the “regular” and the “premium” fuels.
I have been running a spreadsheet on my fuel usage for over a decade. In that time, not always by choice, I have had to run the lower grade fuels instead of my preferred “premium”.
Subjectively my car does run “sweeter” and smoother with consistent power uptake when filled with the 98 octane premium over the 95 and 91.
Objectively, the cost is less with the premium than the lesser fuel. With the non premium I have had the cost per kilometre go to 12cents whereas with the premium it has been consistently 10 cents per kilometre.
It is very easy to set up such a spread sheet in such utilities as Numbers, Excel or in Libre office. For the sake of it, I also see my consumption in Litres per hundred, Miles per gallon and kilometres per litre and see the costs per kilometre.
Paul is correct in his point that the computer engine management systems in most contemporary cars, the spark timing and size is optimised by reading the oxygen sensors in the exhaust as well as knock sensors on the block. Even the timing of at least one set of valves can be varied along with their amount of opening to best suit the immediate conditions.
As far as chasing the more consistent and better octane Avgas is concerned, as it still contains tetra-ethal lead, it is illegal to run any road vehicle with it. (And it can foul the matrix in the catalytic convertor.)