Petrol quality in Taiwan?


short question: is there anything wrong with the petrol (gas) in Taiwan?

Or why does every Taiwanese I know refuel with 98 octanes instead of the manufacturer recommended 95 (huge stickers next to speedo on MBenz and Toyotas) and 95 instead of 92 in their scooters?

Is this voodoo stuff (more pricey must be better) or a sane reason behind it?



In the States, they don’t even sell 95-octane or 98-octane gasoline (petrol)!

The “regular” gasoline (petrol) in the States is only 87-octane, and they also sell 92-octane or sometimes 93-octane, but nothing more than 93-octane.

Several websites, including this one, explain that the engines in all cars (except racing cars) are actually designed for 87-octane, so using anything more than 87-octane causes your car engine to run worse!

The octane number means the equivalent percentage of iso-octane which would cause the same amount of “knock”. (“Knock” is a pinging sound caused by the fuel spontaneously igniting from compression before the spark plug fires, and it’s very bad for the engine.) If a car engine doesn’t knock when using 87 octane, then there’s no reason to use gasoline with higher octane because the “octane rating” just refers to the amount of anti-knock additive (usually MTBE) that is added to the gasoline.

Gasoline is a mixture of mostly octane (C8H18) and heptane (C7H16). Octane almost never spontaneously ignites no matter how much you compress it, but on the other hand, heptane spontaneously ignites very easily. So if gasoline is 87 octane, that means it resists knock the same as a mixture of 87% octane and 13% heptane.

But unfortunately, 87 octane gasoline isn’t sold in Taiwan, even though it’s what most car engines are designed for. So in Taiwan, we have to settle for 92, but that’s certainly much better than 95 or 98.

Here is a couple of very interesting quotes from this website:

Since 87-octane gasoline isn’t sold in Taiwan, I wonder if the engines of cars sold in Taiwan are designed for 92-octane gasoline? But I doubt it. I don’t think the engines of cars imported to Taiwan are calibrated any differently than if they were exported to any other country.

Petrol sold in Europe is 95 octane as standard, with 97 octane also available. Leaded petrol is available for vintage cars, mainly through the Thrust service station network (at least around where I used to live). Certain older cars (such as the Triumph 2.5 PI) use 5 star petrol, which is 100 octane. I don’t know if you can get it any more.

There was also 2 star (90 octane) for lawnmowers, 3 star (94 octane) for small cars (I remember a Peugeot 104 which could just about run on 3 star), and 4 star (97 octane) for normal cars.

I would be interested to know what modifications the likes of BMW and Jaguar make to their cars for them to run on 87 octane fuel. Or vice-versa for the US cars in the UK. A mate of mine used to have a Dodge Charger (Dukes of Hazzard!) and he put 4 star in it. Would that have been designed to run on 87 octane fuel? What about all the Jeep Cherokees in the UK - they’re running on 95.

Some info here from the Automobile Association:

5 star for your mad sports car:

A rant about the phasing out of 4 star:

Ahhh. Maybe this is it: does the USA use MON instead of RON ? 4 star is 97 RON, but 86 MON.

That is not correct. There is no standard for all cars concerning octane. The octane rating required for an engine depend’s on the engine’s compression ration. A high compression engine (which has more kick) needs a higher octane fuel to prevent pre-ignition. If ALL CARS were actually designed for 87-octane, then that would mean that they all have a compression ratio of something like 8:1 or 9:1. There are plenty of cars in the States that need up to 93 or 94-octane fuel. More and more passenger cars are equipped with higher compression engines that need higher octane fuel. My mothers Mazda (not a race car) has a compression ratio of around 11:1, so the owner’s manual recommends 93. If you put 89 or 87 in, it knocks like a bitch.

You may notice that pickup trucks usually use 87 octane fuel. Since pickup trucks are made to haul stuff, their gearboxes have lower gear ratios than passenger cars. A vehicle with a low ratio gearbox needs a lower compression engine to avoid stalling under load. High compression engines are generally no good for taking a load. The added load will make them knock more.

I don’t know why petrol in Europe has a higher octane rating, but I do know that most Taiwan cars don’t need it. I had this discussion with a few Taiwanese friends who insisted on putting the most expensive gas in their tanks. I Looked at about half a dozen of their owner’s manuals. They all had recommendations of between 87 and 93. The compression ratios weren’t especially high.

I don’t believe that higher than necessary octane would cause an engine to run worse (unless maybe it is just way too high, as in 100 for an 87-octane engine). If this were so, your engine would not be able to burn all the fuel on each ignition stroke, and you would notice that. The sparkplugs on any engine are more than enough to fully ignite any type of petrol, so long is the engine is properly tuned. The only bad thing about buying unnecessarily high octane petrol is wasting money.

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I think the differences in octane that you see in Taiwan vs. the US are how the number is calculated. Taiwan probably uses RON (Research Octane Number), while the US generally uses RON+MON (Motor Octane Number)/2, which is usually abbreviated (R+M)/2

For example, what you see at the pump in US as 87 octane would be MON 82 and RON 92, to give you 87. If Taiwan is using RON, then this same octane rating in Taiwan would be listed as 92.

So Taiwan’s 92/95/98 most likely corresponds to 87/89/92 in the US.

That’s my guess.

Some higher performance cars are designed to run on higher octanes (92 (R+M)/2 or 98 RON), for increased performance. This is usually noted with some kind of “Premium Fuel Only” label on the filler cap or fuel gauge. While lower octane will work in these cars, it is because the engine computer can detect the lower octane, and reduce the power output of the engine to prevent against knocking. You will notice decreased power from the engine, however.

If your car was designed for only 87 (R+M)/2 or 92 RON octane, then using higher octane won’t give any benefit.

Just use whatever the manufacturer recommends for the car. It should be in the manual somewhere. If it says “Premium Fuel Only” or something like that near the filler cap or the fuel gauge, then you need to use 92 (R+M)/2 or 98 RON.

More to the point, is there any difference between the gasoline at Formosa and CPC? My Vespa man reckons there is.

There may very well be, and is subject to much discussion/debate. It really depends on a number of factors, including, but not limited to the age/quality/condition of the underground tanks, the additives in the fuel, the formulation that the parent company uses, etc., etc. If you notice your Vespa running worse on one brand of gasoline, or even from different stations within the same brand, it would probably be a good idea to try another brand/station.