Ran the first 100k on mainly 95 occasionally 99 for bit of a clean

Upon discovering tesco momentum is only 9p dearer ive used that for the last 25k

Being a private hire driver and using a lot of fuel i've recently gone back to 95 with the costs

Its coincided with an engine rattle under load

If it is down to change of fuel will the engine adjust and rattle disappear sticking with 95 or am I best going back to 99 ?

Car is a octavia 3 1.5tsi 2019

It's purely coincidental. This is taken from another post a week or two ago -

The difference between '95' and '99' fuels (and others) are a few things. Firstly, the more premium fuels have a higher octane. This makes no difference unless you are driving a 488 Pista, or a heavily tuned car. It is true that your car may run a little better (higher mpg, etc), but this is only true because a given amount of fuel has more 'go' in it - it's a moot point, as the more effective fuel, is more expensive. This difference is also quoted to be around 2%. Not worth it. The second difference is the (bio)ethanol content - E5 vs E10. E10 is the cheaper stuff, and contains, you guessed it, 10% of bioethanol. This stuff isn't the kindest to seals, hoses, etc, but unless you're driving a Mk1 GTI, you should be absolutely fine. The nicer fuels tend to have up to 5% of bioethanol in them (sometimes none), which makes them older car friendly. Finally, the premium fuels also contain additives and cleaning agents that help keep things running smoothly. This is the only real advantage of using premium fuels and, even then, can likely be achieved by using a bit of 99 once every few fill-ups.

I run my car on 99 because I can. It doesn't make much sense to, if I'm honest, and I definitely wouldn't be putting tanks of the stuff through a 1.5 - total waste of money. Given that you do the miles, I'd personally put in some nicer stuff once every three fill ups. Sorted.

Prescribed fuel for Mk2 Fabia vRS were Super Unleaded is Super Unleaded 98. Except 98 stopped being sold in the UK, so you got 97 or 99 min. Obviously you could run on 95 ron, but as many of us know, not so well. The recommended octane was also 98 ron for GTI.s & R,s. Golf, Sirocco, Polo etc, Not all E10 has 10% bio, it can have up to, and not all E5 has 5% Bio Ethanol. Even Momentum 99 E5 in the UK is not the sdame around the country, or ESSO Synergy as delivered by Greenergy. Fuel consumption need not be increased, but emissions might well be reduced. Petrol formulation changed in March delivery in the UK. Winter formulation is less Hygroscopic. E10 % E5. and the E5 might well be above 99 ron as Continental Super unleaded of 100-102 ron might be brought in.

Edited 21 April21 Apr by Evolution13

At least Tesco showed testing results. 14 years ago.

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Edited 21 April21 Apr by Evolution13

Given how the question was framed, I copied my general reply from another post. It was about air filters or oils, IIRC, so it wasn’t very specific. Of course different fuels have different formulas, and winter mixes are different to summer.

Of course manufacturers will recommend you run expensive fuels, just like they only recommend genuine coolant, oil, parts and OE approved tyres and wiper blades.

Like I said, unless the car is a performance car, or is heavily tuned (probably less than ten cars on this entire forum fit into this category), the difference in fuels is going to make absolutely no difference. I know someone that puts 95 into a GT4 RS, and it hasn’t gone wrong yet. I don’t know enough about the earlier Fabia vRS to comment, but I really can’t see them requiring a higher octane fuel when an M5CS doesn’t. Do dealers fill them with 99 before sale? I doubt it.

Besides, OP was asking specifically about the 1.5 petrol engine in his Octavia. You couldn’t get much further from a performance engine if you tried - running 99 or 97 versus 95 will make absolutely no difference. It just won’t.

Of coarse they run OK in the EU / Europe / UK and elsewhere on 95 Octane petrol. But even if there is no noticeable economy improvement on higher octane in the UK at National Speed limits there can be even more efficient running and that might just be smoother driving. Good that the choices are there to buy what ever it is you want. So lets stick to 1.5 TSI,s that as the WLTP came in VW messed with to get WLTP & RDE2 certification. They messed withe the Mapping / Engine management. They built in a lack of torque with some. Eventually a DVLA Safety Critical Racall was started. This was about the Kangerooing. Not only Manuals but more noticeable than a DSG. But both might have got the 'Software upgrade'. Some were not deemed to need it. Then that should have been that. Fault cars, cars with issues fixed. Well some even later, are just not quite right and if 97 or 99 ron makes them feel better then that is that, if not then know. Then there are spark plugs, best not leave them too long unchecked with a 1.5 TSI ACT.

As I said, I stick 99 in because I can, and because it can't hurt. Given the miles that OP is doing, I'm not sure it's worth it! We ran previous cars on the cheapest stuff going, and all of them had no issues in the decades of ownership. They were pretty mixed too - all the way from a 1.4 to a 3.2.

Maintenance will have a bigger impact on the longevity of the car than the fuel used.

Private Hire driver, car a necessity and tool of the trade. If £3.00 extra a tank for Tesco Momentuim 99 or Sainsbury 97 ron feels better than 95 ron then 'simply clever' surely to use it. Its an overhead and not a big one.

1 hour ago, Evolution13 said:

Private Hire driver, car a necessity and tool of the trade. If £3.00 extra a tank for Tesco Momentuim 99 or Sainsbury 97 ron feels better than 95 ron then 'simply clever' surely to use it. Its an overhead and not a big one.

Filled up with momentum today , price come down 6p since last visit, see how i get on