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What are your opinions on E10 petrol? How much of an impact have you noticed if any? Is it worth paying the extra for premium? TIA!
 

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I know I have a diesel but I recently had my other petrol car on a rolling road session and the tuner told me he had left a bottle of E10 to stand and after 2 weeks, it had completely separated into water and ethanol (or whatever the other bit is?).

In other words, if you expect the car to stand for more than 2 weeks, don't use E10 (water is very bad at combustion :) )

As to other 'benefits' of premium, I'd be very surprised if you noticed anything with these types of car - maybe on a track but not in normal use. I often read of people saying, "yeah, premium is much better, feels faster, smoother" - personally, I think that is in their heads, to justify to themselves paying the extra ;-)
 

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I'd say it's probably not worth the extra outlay unless you're driving something with a good bit more performance and then you might notice the difference. If there's any gains to be had on a petrol Kodiaq, then they would be very slight and probably not really noticeable in the real world.

My wife's aunt only uses premium petrol in her BMW 320i and is adamant that it's faster because of it, but I'd be amazed if you could actually tell the difference and if you accurately measured it with a proper GPS-based tracking system, then the difference would be so slight as to be insignificant.

As for the water separation issue, then yes, ethanol is very hydrophobic and will absorb water from wherever it can, including the atmosphere, but unless you're storing your petrol in jerry cans before putting it into your car, then this really isn't an issue you'd ever notice. And the issue was still there when we had E5 fuel, which we've had since 2019.

A few years back I had an independent mechanic who would show people a jam jar which he claimed came from a supermarket forecourt and it had loads of bits floating about in it. The 'story' was that you shouldn't buy petrol from supermarkets because they have such high turnover of their storage tanks that any sediment never gets a chance to settle and you end up pumping the [email protected] into your car. But if that were true (and a problem) then there would be loads of cars breaking down with blocked fuel filters and this just isn't the case. It's just a scare story in the same way that water separation for E10 is. Austria have used E10 for nearly 20 years and there's nothing special about cars sold in that country, they're exactly the same as those sold here when we had E5 fuel.

Ultimately if you're in the fortunate position to be able to afford premium petrol every time you fill up, then knock yourself out. It undoubtedly includes better aditives to keep the interior parts of your engine clean, but if you want that benefit then don't mix it with E10, but stick to premium all the time. Lucky if you can afford this I'd say!
 
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I know I have a diesel but I recently had my other petrol car on a rolling road session and the tuner told me he had left a bottle of E10 to stand and after 2 weeks, it had completely separated into water and ethanol (or whatever the other bit is?).

In other words, if you expect the car to stand for more than 2 weeks, don't use E10 (water is very bad at combustion :) )
Whatever parts it separated into, one of them was not water. Pure ethanol is quite hygroscopic (not hydrophobic which I think is a typo in the other post, as that word means ‘repels water’) and will absorb water, not seperate from it. Some very old bottles of whisky will attest to that lack of separation. If the separation your tuner describes is not an urban myth (seems very fast), the other fraction is petrol, of course. So the car will be fine driving off with that, and the movement will mix the parts up again. The engine computer will deal with any uneven mixing by adjusting the fuel/air mix and spark timing based on the combustion sensors - same as it would if you vary the grade of petrol you fill up with.

Whilst ethanol, as a polar solvent will absorb atmospheric water, as long as you leave the petrol cap on, there won’t be a lot there to absorb. While some air is drawn in to replace outgoing fuel, it’s not really a breeze in there.

Ethanol does burn hotter than petrol, but at E10, which is still 90% petrol, that’s not a problem. Special designs are needed for 100% ethanol engines however.
 
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Whatever parts it separated into, one of them was not water. Pure ethanol is quite hygroscopic (not hydrophobic which I think is a typo in the other post, as that word means ‘repels water’) and will absorb water, not seperate from it. Some very old bottles of whisky will attest to that lack of separation. If the separation your tuner describes is not an urban myth (seems very fast), the other fraction is petrol, of course. So the car will be fine driving off with that, and the movement will mix the parts up again. The engine computer will deal with any uneven mixing by adjusting the fuel/air mix and spark timing based on the combustion sensors - same as it would if you vary the grade of petrol you fill up with.

Whilst ethanol, as a polar solvent will absorb atmospheric water, as long as you leave the petrol cap on, there won’t be a lot there to absorb. While some air is drawn in to replace outgoing fuel, it’s not really a breeze in there.

Ethanol does burn hotter than petrol, but at E10, which is still 90% petrol, that’s not a problem. Special designs are needed for 100% ethanol engines however.
Ah yes, of course, I did mean hydroscopic - you're absolutely right that hydrophobic is the complete opposite!

That said, there are a few places on t'interweb that describe exactly this phenomenon. This one for instance:
Phase Separation = Water + E10
Basically I'd take the story that the petrol and any water/ethanol would separate after just 2 weeks with a huge pinch of salt - it just doesn't happen that quickly unless you pour some water into the petrol, in which case it will happen within a few minutes...
 
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