Morris Minor Owners Club

I’ve heard rumours that ethanol levels in Esso super unleaded are rising, and wondering if there’s any truth to this.

The standard line is that Esso Synergy Supreme 99 can contain up to 5% ethanol, but it appeared that super unleaded sold in the south and some other areas was reported to contain no ethanol at all. So I’ve been using it exclusively for many years.

Does anyone know if Esso’s super unleaded is still ethanol free in the south?

I'm not aware Esso do a super unleaded. They do Synergy Unleaded 95 which is 'up to 10%' ethanol and is best avoided in a Morris unless needs must in which case put in just what you need.

They also do Synergy Supreme+99 Unleaded. This was traditionally 0% ethanol in most, but not all, of the country. However, that changed in September 2023 when it became 'up to 5%'. This is still the case today.

As Keith says...
Until 2023, the ESSO website included a note to the effect that due to refinery positions, distribution systems etc, a certain part of the country in the south was not getting any ethanol added to it's Synergy Supreme+99.
That statement was then removed and all Synergy Supreme+99 is now up to 5% ethanol.

Quite honestly, so what.
There is too much ignorance of fuel history; Ethanol was mixed in fuel for nearly a century and nobody batted an eyelid.
In the 1920s and 30s, Ethanol was used as an octane booster as was lead and other substances.

Cleveland Discol was a popular alcohol-blended petrol sold in the United Kingdom from 1928 until 1968.

ESSO started acquiring shares in Cleveland Fuels in the mid 30s, had full control of it from mid 50s and rebranded totally to ESSO around the time of the 1973 Fuel Crisis.
There was always an unspecified amount of ethanol in many fuels worldwide, until the oil slump of the late 1980s when the oil price dropped to about $12 a barrel and many ethanol producers went bankrupt.
Then when people woke up to the dangers of other octane boosters, like lead, ethanol came back into favour.
But now in the world of Social Media and Fake News, the Pros and Cons of everything are exaggerated.


https://youtu.be/4uEqqlqqf4Q
.

There are only 4 refineries in the UK, many are branded product for different sellers and possibly but not always different blends.
Bit like badge engineering of cars.

I am not concerned whether a fuel contains 5% or 10% ethanol. What I am concerned with is sticking to the same, or very similar, octane rating once the car is properly tuned for ignition timing and fuel mixture. The reason for this is that the engine is not a modern engine managed by a computer. Once set up for timing and mixture that's how it stays. If you tune it using "Super" with an octane rating of 98/99 and then fill it with 95 it just won't run as well. It won't make a lot of difference unless you have used the "advance until it pinks and back off a bit" method of setting ignition timing. If you have sailed close the wind it may just pink on lower octane fuel.

Having said the above, I do routinely use Esso 99 because there is a very convenient Esso filling station close to me and I have an Esso fuel card. Also, ethanol is hygroscopic and contributes to fuel tank corrosion if stored for long periods (e.g over winter) so I would rather use 99.

Stephen

geoberni wrote: ↑Tue Mar 03, 2026 12:43 pm
Quite honestly, so what.
There is too much ignorance of fuel history; Ethanol was mixed in fuel for nearly a century and nobody batted an eyelid.
In the 1920s and 30s, Ethanol was used as an octane booster as was lead and other substances.

If like me you are running a vintage motorcycle with a fibreglass tank so A LOT

The tank 'dissolved' with E5 fuel ...the resin leeched out and re solidified in the carburetter

Had to cut out the base of the fibreglass tank and fabricate and fit a custom steel liner

Taupe

taupe wrote: ↑Tue Mar 03, 2026 5:33 pm

geoberni wrote: ↑Tue Mar 03, 2026 12:43 pm
Quite honestly, so what.
There is too much ignorance of fuel history; Ethanol was mixed in fuel for nearly a century and nobody batted an eyelid.
In the 1920s and 30s, Ethanol was used as an octane booster as was lead and other substances.

If like me you are running a vintage motorcycle with a fibreglass tank so A LOT

The tank 'dissolved' with E5 fuel ...the resin leeched out and re solidified in the carburetter

Had to cut out the base of the fibreglass tank and fabricate and fit a custom steel liner

Taupe

OK, I was talking classic cars, not bikes, since we're a Minor Forum.

I'm aware that if the 'incorrect' resin was used with fibreglass fuel tanks the ethanol reacts with the cured resin...Presumably a classic cycle could have such 'unsuitable' resin in it's fuel tank construction if it falls in the right period when ethanol was out of fashion....
Not being a biker I don't know when bikes started to use fibreglass tanks.
When the whole E5/E10 thing kicked off, which seems like years ago now, in the stuff I was reading there was discussion about classic bikes and using epoxy-based sealers for fuel tanks.

I know it's been a problem in boat building for decades, as the ethanol resistant resins are more costly than regular resins.

Yes I think they use vinyl ester resins (also epoxy type probably) etc now which are more resistant

T