Supreme Unleaded - Yes or No?

[N-Dog]

Quick question for you.
In my 'everyday' car, a 2013 1.6 litre Mazda, I occasionally fill up with Supreme grade Unleaded.
I can feel the difference and I think it runs a little smoother, and returns a slightly better MPG.

Are there any reasons why I SHOULD or should NOT do this with my 2.0 16v Cavalier, X20XEV ?

[Robsey]

Being a later 16 valve engine, I assume that your car is fitted with a knock sensor.
If so, then I assume that it will be safe to run the car on super unleaded - 98 ron.

None of the 8 valve cat equipped engines that preceeded the LET / XE / XEV engines appear to support super unleaded fuel.
Not unless they are fitted with an Octane plug with 98 printed on it.

Where a 98 coded Octane plug is fitted, or a knock sensor is fitted, then it is understood that super unleaded can give a perceived improvement in responsiveness, but no benefits in fuel economy or running costs.

[N-Dog]

OK many thanks for that Robsey, I guess that if it won't do any harm, I'll use it. Not that the performance needs improving - it's got more guts than my Mazda anyway!

[James McGrath]

It won't do any harm at all to use super unleaded fuel. In fact it will probably do it some good as most super unleaded fuels contain cleaning agents to keep your engine clean.

You can use it in any MK3 Cavalier however, as Robsey pointed out, only some engines can make use of the higher octane rating to improve the performance.
Your engine, (The X20XEV) can make use of it and you should get a very slight power and MPG improvement.

I always use it in my 1.6i SPI as the higher octane rating helps to prevent pinking. It doesn't help improve the performance but the engine does run better using it.

On a side note, there is a whole other debate about the ethanol content of modern fuels.
All regular unleaded fuel contains at least 10% ethanol. This is absolutely fine for modern engines that are designed for it however, some say that it can cause harm to older engines.
All the engines used in the mk3 Cav are actually pretty modern designs in the grand scheme of things and are probably fine using this fuel but the fuel lines are not. Ethanol can eat through rubber fuel lines if they are not designed to carry it.
Ethanol is also hygroscopic (attracts moisture) so if it is left for long periods of time water can build up in the fuel tank and fuel lines causing corrosion.

Most super unleaded fuels do not contain ethanol.
I've had problems with leaky fuel lines on all of my Cavaliers apart from my 1.6i SPI (which always uses super unleaded) in the last few years and I'm sure it's because of the ethanol in normal fuel.

[T1BBST3R]

I heard the high octane fuels are 15% bio ethanol which burns hotter than normal petrol. Usually fuel is 3% bio ethanol if I remember correctly but different fuel companies like to tweak their fuel about differently to eachother anyway.
Best fuel for older cars (from before the days of bio fuel) would be bwoc or any other fuel that doesn't contain any bio fuel and it should smell kind of like oily fish. That would make your engine last the longest. Supermarket fuel would be the worst.
Saying this, I am a long way from any bwoc garages as they're few and far between so I just fill up at BP stations but their petrol does smell quite oily still even if it is 3% bio fuel. You don't want petrol smelling of alcohol, anything over 15% bio will wreck any engine not designed for it which is why you don't get a higher ratio at pumps.

Most countries run on 90ron fuel so 95ron is still pretty decent.

[Robsey]

I see you mention BWOC as being best for older cars, and supermarket chains are the worst.

A search on their website clearly lists Morrison's supermarkets, along with many Esso and Texaco fuel stations.

Although, I cannot fathom whether these garages supply BWOC fuel, or just accept the BWOC fuel card.

I have run my Cavalier for 24 years and 269,000 miles mainly on Morrison's unleaded. Maybe I am just lucky.

I have tried BP super unleaded once or twice, with no apparent gains being noted.

[dorsetdave]

Back in 1982 I gave up the unequal struggle with Cortinas as my Company cars and went on to the Cavalier. I still have the original brochure that I used to spec. the car. I shows that all Cavaliers were designed to run on up to 6% methanol. Did that specification change over the years?