Hi, Not sure about the MK3 1.8 but surprised it states 91 if in the UK. Normal unleaded is E10 & 95 Ron. Super is E5 & 98+
Perhaps the MK3 1.8 was designed to use 95Ron, All other TT Marques were designed to use 98+ for max power & efficiency.
Hoggy.

 

don't know if situation changes for UK (I would say not), but for Germany and Italy at least, all TFSI engines are tuned to run with 98 ron for best performances. you can refill with 95 ron without causing any damage to the engine, but obviously the efficiency will be reduced

 

Look inside your fuel filler cap for the correct grade of fuel. The 1.8 and AFAIK the standard 2.0 are designed to run on 95 RON. You can safely put 98 RON in but you won't see any difference in performance or economy, just a bigger hole in your wallet.
However now that 95 RON is E10 with an apparent 3% power / mpg loss, you could recoup that by filling up with 98 RON which is still E5.
Different matter for the S models which will run best on 98 RON and lose some performance on 95 RON.

 

Thank you for the responses. This is what it has printed on the fuel cap. The fuel hoses at Tesco were labelled premium at 99 and normal at 95, hence my confusion. I put in a small amount of 95 (which Tesco labelled as basic unleaded) as was worried the 99 wasn’t listed on the fuel cap. The car is the 1.8 sport.

 

Hi, Yes, unusual I would think for a UK 1.8 to be labelled 91 as it's not normally available in the UK.
If you like to use the performance use 99 ron which is a max of E5 ethanol.
If you are stuck in commuter traffic most days, use normal 95 Ron
Hoggy.

 

Thank you, really helpful.

 

As others have said, 95 is safe to use but even with the 1.8 it’s been shown that you only get full power with 99 (I’ll try & find the info for that & link it) so best to use 99ron. Also, as others have said, 95 is now e10 meaning you’ll get less miles per tank due to the ethanol content.

95 Ron - Normal Fuel
99 Ron - Premium Fuel

E10 - 10% ethanol. Safe to use but ethanol is less energy dense than petrol.
E5 - 5% ethanol. What it’s been for a long time.

 

This is a really complex area (ethanol content) as ethanol in petrol actually increases the octane rating (ethanol neat is about 105 octane I believe), so I'd imagine if ethanol is roughly 70% the energy density of petrol then going from E5 to E10 is only going to affect most petrol cars by maybe 1 or 2% mpg at worst. If the engine is high compression/turbo/sufficiently intelligent, you might actually get more performance/range from the higher octane fuel.
Any chemical engineers on here?

 

This is where I got my info, but I ken it’s a lot more complicated. Still worth a look & help inform your decision.

 

Yes it is a complex issue. The general consensus when E10 was introduced was that we would experience a 3% drop in mpg. However since then I can't say I've noticed any significant reduction in mpg, although that's only looking at the mpg readings given on the dash.
I did do a test some years ago on my Scirocco which was designed to run on 98 RON. I did some extensive mpg checks using 95 RON and 98 RON over several weeks. After doing the 95 RON tests I ran the tank down and filled up with 98 but ignored that first tankful until I could fill up again with 98. I did the tests over 3 tanks of each making sure that conditions like ambient temperatures, driving routes and traffic conditions were similar.
In the end I found I was getting 3% more mpg from the 98 RON, which at the time more than covered the extra cost.
A few years ago I did a similar test in the my TT which is designed to run on 95 RON. I found I got absolutely no difference in mpg by running it on 98 RON.

 

Thanks guys. It is indeed very complex. Based on your responses I think I will use the 95 for my usual short trips and if I am planning a longer trip will fill up on the 99.

thanks again