Car Care: Avoid paying too much at the pump

By Jack Biddle

Using the wrong octane petrol can add to your fuel bill.

Picture / APN
Using the wrong octane petrol can add to your fuel bill. Picture / APN

Ways to stretch the family fuel budget With fuel prices on the rise again, it's timely we cover some steps you can make to get the best fuel economy out of your vehicle.

But it's important to avoid overreacting to an increase in pump prices. It's not uncommon for some owners to think about downsizing and/or investing in a more fuel-efficient vehicle when fuel prices increase.

But, in some cases, it may inflict more financial pain to change vehicles than it would to spend a little more at the petrol station.

On the used car market, it's not uncommon to see large vehicles drop in value and also become a lot harder to sell when fuel prices increase.

The opposite can apply to the smaller, more fuel-efficient fleet; they can become a lot more desirable and prices can therefore increase.

For some owners also, a large car can be a necessity because of family or lifestyle needs so downsizing can be impractical.

So what else can you do to stretch the family fuel budget? Underinflated tyres can increase fuel consumption by as much as 7 per cent while those who drive with an erratic throttle control can consume up to 20 per cent more fuel.

The other big fuel consumer is short drives on a cold engine.

But what about the octane level of fuel you are using? Essentially there are three grades of petrol available to motorists. First is the cheaper and lower grade 91 octane, followed by 95 octane and finally the more expensive and higher grade 98 octane. (For simplicity we will ignore the ethanol blended fuels that are also available.)

Some motorists believe filling up with 91 octane means less bang for their buck and by using the more expensive higher octane fuel their vehicles will perform better and fuel consumption will improve.

In all the fuel testing I have been involved with, this has never been clearly proven.

Gains are minimal at best and when a margin of error is factored in the benefits are insignificant.

For the majority of vehicles on our roads, fuel octane requirements are based around the engine's internal compression (air/fuel) ratio or the tolerance/pressure the fuel has to withstand during the compression stroke without self-detonation taking place. Lower-compression engines therefore require only the lower octane while the high-performance engines which have greater compression ratios require higher octane fuel.

Where it all gets very confusing is not all gas stations sell the same octane rating petrol.

All sell the cheaper 91 octane while there are some which sell 95 and others that sell 98 octane as the alternative fuel. The difference in price can be around 8c a litre so if you are using 98 when the engine requires only 91 octane, then you can pay around 16c a litre more than you should. Confused? Let's try and make it a little easier.

Most vehicles on our roads can operate without any issues on 95 octane so if in doubt it's the fuel to use. However, a large percentage also happily accept 91 octane fuel with no problems. Very few (probably less than 1 per cent) need an octane grade higher than 95.

So what is the golden rule? If your vehicle is designed for 91 octane then use it (check with the franchise holder or your preferred repairer), if in doubt use 95 octane unless you have an extremely high-performance vehicle (unlikely).

Next step is to check which of your local stations sells the grade of fuel you require. Fuel stations don't make it easy as they generally display only the price of their 91 octane fuel.

Yes, it gets a little complicated but by changing fuel sites or octane level, you may automatically reduce your fuel bill or at worst pay a price similar to before the latest increase, or the one before that in some cases.

- NZ Herald

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