5S-FE fuel?, What fuel to use? Options

[UVZ164]

Hey guys, I'm kinda new here and not sure if this is the right place to post this.

I did a search but couldn't find the specific answers I wanted so I thought i'd ask.
I live in Sydney Aust and the fuels available to us are: E10(10% ethanol) 91 octane, and regular 95 and 98 unleaded.
I recently bought a ST204 ZR which is the equivalent to the American GT. It runs the 5S-FE.
The guy I bought it from told me to steer clear of the E10 as it will ruin the engine. As my wallet isn't that deep I decided to give the cheaper E10 a go.
After about a month and a half of running the E10(i'm assuming the previous owner used 95) i'm beginning to hear a noise almost like tapping when I rev the engine above 3k rpm and just let it decrease naturally. As it never made this noise before, could I be right in assuming that the E10 is doing something and possibly ruining the engine? The owners manual states that 91 octane is as low as you can go but it doesn't say anything about Ethanol.

Thanks in advance,

Reece

[Galcobar]

There's a difference between cheap fuel, which may not be as high quality, and low-octane fuel, which will be of equal quality but has less octane (and sometimes other non-essential but nice-sounding cleaning additives).

Crap fuel, of any octane rating, is bad for your engine.

Low octane fuel is only bad for your engine if your engine actually needs the high octane levels -- typically, in higher performance/compression engines. The 5SFE is designed for low octane fuel. In North America, 87 gas is sufficient and recommended in the Celica owner's manual for the 5SFE. Using higher octane numbers just means the ECU has to compensate by altering the timing -- it doesn't gain you compression or performance.

Different countries use different measures for the octane number.

North American pumps display the rating as a function of (R+M)/2). The vast majority of the world, in this case notably Australia, uses the Research Octane Number. North American pumps for the lowest-end gas show 87, while European/Australian pumps would show 91 or 92 for the same gas.

Ethanol acts much like octane, so when using a blended gasoline the octane rating you see is based on its equivalence to a gasoline/octane mix. From your engine's timing perspective they're the same in regards to delayed detonation.

The danger of ethanol is to some (mostly natural) plastic and rubber. While the 10% ethanol does a great job in reducing CO2 emissions (it replaced MTBE which pollutes ground water, though modern electronic AF management has largely made it pointless) it absorb waters far better than gasoline and thus is more likely to dry out those rubber and plastic parts. However, modern neoprene rubber is not affected by alcohol exposure and was in common use by the mid-1980s, most notably in Japanese vehicles. Vehicles made in the 1990s, unlike small engines found in chainsaws and the like, should not suffer parts failure because of ethanol unless someone goofs in the design (Toyota did notably a few years back, prompting a recall of leaky fuel systems).

There is a significant danger, however, in switching from straight gasoline to gasohol. It's the same danger as running a concentrated fuel cleaner such as Seafoam through your system (which is why Seafoam is careful in its instructions about properly dilution); accumulated gunk is dissolved, and then has to travel through the fuel system. Most vehicle failures associated with gasohol are actually due to this rather than parts corrosion. Twenty years of gunk released in one shot is liable to do some damage. Between the relatively mild E10 blend and it being in place for some years, if you haven't had that failure yet you're not likely to now.

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That said, most of the above is irrelevant to the OP's original question. Short form: using the recommended fuel in your vehicle is not going to cause your vehicle to fail. An Australian gas with an octane rating of 91 is quite sufficient. More likely is that your 12- to 17-year-old engine needs some work, which might be as simple as a valve adjustment. If your engine was pinging due to low octane values allowing for premature detonation, your knock sensor would let you know.