I am only paying RM 2.62 per litre for petrol

Yes the title says it all, I am only paying RM 2.62 per litre for petrol. And no, this has nothing to do with any credit card promotion or anything like that. It's just one of those lesser known good deals. To purchase petrol at RM 2.62 per litre simply involves switching to a lower octane rating fuel, albeit one that is slightly less widely available. Those of you who know what am I on about can skip this entry. I am posting this up because I realise that a surprisingly large number of motorist do not understand the meaning of octane rating in their fuels, and then there are those who think they know but are actually mixing them up with many myths and misconceptions.

Ever since the Malaysian government raised the prices of gasoline to RM2.70 per litre (unlike many countries, Malaysian government determines the prices of fuel, which are sold at subsidized prices), I have since switched from being a loyal Shell motorist to a Caltex user. This is because Caltex is one of the few oil companies that sells a lower octane rating RON 92 petrol, at RM2.62 per litre. The standard RON 97 petrol retails at RM2.70 per litre at all gas stations in Malaysia. Most modern petrol engines have no problem running with petrol with as low as 90-octane.

So what the heck is this octane rating? Octane is a measurement standard for autoignition properties of a fuel. To explain further why we need to have an octane rating for petrol, we need to understand how a typical engine works. The animated gif below is a simple example of a 4-stroke Otto cycle engine that is used in most cars.


Image from WikiMoto
Without going into too much details, the first cycle starts with the mixture of fuel / air (blue) being drawn in, which is then compressed by the upward motion of the piston. For optimum performance and efficiency, the spark must ignite the fuel at just the right moment (engineers call it TDC, top dead center). This is where the octane rating of a fuel comes in. A lower octane rating fuel will ignite on its own due to the high pressure and temperature, before the spark is being delivered. This condition is called pre-ignition or auto ignition, which is not something you would want unless you are talking of a diesel engine (compression ignition), but that's another story.


Anyway in petrol engine, pre-ignition will result in "pinging," a condition when the engine sounds like "marbles" rolling around inside it due to the many uncontrolled explosions all happening at the wrong time. And of course, a higher octane fuel will be able to withstand higher pressure and temperature before being ignited. High performance engines usually run on higher compression ratios, thus requiring higher octane fuels. And if you are still up for more information, octane is measured ("calibrated") against a mixture of iso-octane (Octane-100) and heptane (Octane-0). A fuel of 97-octane has equal auto-ignition properties to a mixture of 97% iso-octane and 3% heptane.

Now that the we got the mind-boggling bits aside, the reason most Malaysians are not aware that lower octane fuels are available is because oil companies don't offer it widely in the first place. And those that do, don't quite publicise it, choosing to focus their marketing efforts on the higher priced 97-octane petrol. I guess it has to do with Malaysia's policy of controlled fuel prices. Thus, oil companies prefer to sell just one type of octane rating. Note that premium grade fuels like Shell V-Power have nothing to do with having a higher octane rating. Those fuels deliver better performance from their additional additives formulated to the fuel.

A typical Shell fuel pump in Singapore, where fuel prices are floated in a free market. Note the different grades of petrol with various octane ratings. Image from AsiaOne.

So the question is can your car run on 92-octane fuel? The best way is to confirm with your owner's manual and look under fuel systems or something like that. Most modern engines now only require fuels with 90-octane and above. Having said that, if your car's owner's manual states that the minimum octane required is 90-octane, you are not going to get any improved performance from using a higher 97-octane fuel. Like I said, octane is just an auto-ignition property. It has nothing to do with quality of fuel nor does it have any influence on your engine's long term reliability. Fuel quality is measured by their sulphur content (which harms catalytic converters), metallic (i.e. lead / copper) and vapor (causes vapor lock). It does not mean that 97-octane fuel is of a higher quality than 92-octane fuel. So if your car owner's manual states use 90-octane fuel, there is no point in paying more for a 97-octane fuel. Don't believe what you read in Ah Beng / Ricers / "tuners" magazines touting octane boosters etc etc.

There will be certain conditions where higher octane fuels is required. Older cars might suffer from carbon deposits in their combustion chambers, thus the effective volume within the combustion chamber is smaller than originally designed, altering slightly its compression ratio and thus resulting in engine "pinging." Switching to a higher octane fuel might solve the problem. But then again many modern engines these days already come with engine knock sensors, which directs the engine computer to retard / advance ignition accordingly to avoid "pinging."

Some argue that a higher octane fuel, due to its higher price, have better fuel additives formulated inside. That's a fair enough argument as there is no common standard for fuel additives used by all oil companies. However, I belong to the school of thought that believes smooth driving, good mechanical sympathy for a car and religiously following servicing schedule is a lot more important than using any fancy fuel to prolong the life of an engine.

Now that you know you have a cheaper option, the choice is yours. Some might argue that a 8sen per litre saving is negligible. But a 8sen per litre saving will translate into a RM3.20 saving for every full tank of an average 40-litre fuel tank MyVi. Multiply that with an average driver going through 3 to 4 full tanks in a month, that's a saving of between RM9.60 to RM12.80. Small figure to some, but there are those who would rather use the savings gained to buy themselves a free lunch or dinner. So if your choice is to give a weekly donation to big oil with no benefit gained for your car, it's up to you. The choice is yours.

Damn, is there anyway I could ask Chevron to pay me for promoting their Caltex Silver with Techron? Then again, maybe they DON'T want to promote it in the first place. Which is why most of you don't know about it!