Silly car question #35: can I save money by just filling up with the cheapest petrol at the pump?
Thursday, 28 June 2018
Petrol prices sometimes seem to just keep increasing, while Auckland motorists are staring down the barrel of an 11 cent per litre price hike when the regional fuel tax is introduced shortly, so could you save money by using a lower octane (and therefore cheaper) fuel?
The answer to that is actually quite simple - no, you can't. And it may even end up costing you even more money in the long run.
Around 90 per cent of the petrol-powered vehicles on New Zealand's roads can run on 91 octane petrol, so really have nowhere left to go short of kerosene (which we most certainly wouldn't recommend), but the owners of cars that the manufacturer's recommend run on 95 octane or higher face the temptation of saving money at the pump by using 91 instead and this can lead to problems, rather than sweet, sweet savings.
If 91 octane petrol is used in cars requiring higher octane fuel, they run the risk of pre-igniting or 'knocking'. Knocking occurs when the petrol combusts early and pushes down against a piston while it is still moving upwards during the compression stroke and it can cause serious damage.
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Although, that said, in a modern engine it probably won't, because modern cars are packed with enough sensors and computing power that they can happily adjust their ignition timing to prevent pre-ignition and therefore run relatively happily and safely on lower octane fuel.
But there is a 'but' and it is a big one.
While it won't damage your engine in the short term (although in long term it could still be a distinct possibility), you will see a loss of performance anywhere from negligible to seriously depressing, depending on your make and model of car.
Loss of performance means you will need to use more throttle to get the car moving at the same rate, meaning you will use more fuel.
Also, 95 and 98 octane fuels burn more efficiently, meaning that you will get more mileage out of a tank of high octane fuel than lower octane fuel.
So, lower performance, less range and the risk of damage ranging from 'probably not' to 'catastrophic' depending on a number of variables really does make the answer to this question anything between 'no' and 'Oh Dear Lord, why would you do that?!'
Adding to the possible risk is that you may even void your newer car's warranty by not running it on the fuel recommended by the manufacturer.
In short, you should be fine using 91 in a car rated for 95 or 98 in an emergency or to save a few cents at the pump if you are feeling strapped that week, but in the long term the risks aren't worth it and the savings just won't be there.
But what about the other way around? Can using higher octane fuel in a car that recommends 91 actually save you money?
The vast majority of cars that use 91 will happily run on higher octane fuel and while you pay more at the pump, you might also see an increase in range from using the more efficiently burning fuel.
That is still just a 'might' mind you, and any gains will probably be set off by the higher up front filling costs anyway. But it will depend on your car and it may even run better.
All up, the potential gains from using a fuel with a different octane rating than that recommended by its maker are largely outweighed by the downsides, the potential risks or the extra cost.
It will depend a lot on your car, but if you are uncertain, then you're best just to stick with what is printed on the fuel flap.