I'm having a long motorway run on Sunday, and was planning on filling up with Super Unleaded for a change to compare the difference with normal 95RON unleaded. However, when I last filled up I didn't really think and filled my tank right up with normal unleaded meaning it's still going to be half full with that come Sunday.

My assumption is there's no real point trying out Super until I've pretty much emptied the standard stuff out? But it also made me think, would there be any negative effect of having a 50/50 mix of 95RON and 98RON?

Having had a diesel for 5 years prior to this car, and petrols before that that wouldn't benefit from Super Unleaded, this is new territory for me.

Worth checking your cars mapped for 98 ron. The sticker under the filer door does it say up to 98 or is it just 91-95ron? If the latter you'll be wasting money over a brand name 95ron for no benefit

If it is mapped to handle up to 98 then yeah a mixture won't give a great indication :-(

hope this helps

I have a vRS TSI - the filler sticker says Minimum 95RON. My understanding is it would benefit from 98RON "out of the box".

Should have thought about it before I filled right up - was only because I was out of my home area and the petrol was cheaper that I thought I'd make the most of it!

If you mix equal parts of 2 different octane number fuels, you typically get an effective octane number half-way between the 2 once you've cleared whatever's in the fuel lines.

I have a vRS TSI - the filler sticker says Minimum 95RON. My understanding is it would benefit from 98RON "out of the box".

Should have thought about it before I filled right up - was only because I was out of my home area and the petrol was cheaper that I thought I'd make the most of it!

The TSI engines are designed to run fine (at full power) on 95 octane fuel and can run on as low as 91 Octane. They have a knock sensor which detects if the fuel is of poor quality and then Engine Management Unit then retards the ignition by a degree or two to preventing the knocking.

95 should be fine most of the time, occasional use of Shell etc is generally thought a good idea because of superior additives in their fuel. Also use of 98 might be advised if you were fully loaded ie 5 people, boot full of stuff and it was hot summer day or to use on a track day. Our TSI VRS seems fine on 95 Octane but we will lob in the occasional (1 in 4 maybe) 99 Octane as it get mixed very quickly by the fuel system and will compensate if one does get a below par batch but the engine is clever anyways so I suggest you mix supermarket and direct oil company purchases. If remapped of course different story, highest octane obtainable.

lol

Edited 9 April, 201016 yr by lol

I understood it could take a tankful or so for the electronics to adjust fully to get maximum benefit from the new octane

I understood it could take a tankful or so for the electronics to adjust fully to get maximum benefit from the new octane

I'd expect these algorithyms to adapt faster if you drive hard than if you're just cruising along on light throttle.

Yeah lol that's a good point -- i said 98ron would be a waste of money in a car mapped for 95ron (real world, it would be a waste), but the engine will probably run slightly quieter on 98ron even though the car's map can only make the most of up to 95ron. Reason would be the ECU wouldn't be running the engine at the point of maximum efficiency for the fuel (just at the point of knock occuring).

Not convinced about lol's idea that 98ron could be advised under adverse conditions, the map coupled with the knock sensor will handle / avoid detonation etc. so i don't think there's any real world benefit to that, although i reckon if you're really anal about it then yeah there will be a marginal, maybe unmeasurable, difference to stress on engine components.

ednmra -- the adjustment at the engine end would be instant, the ECU's almost always (theres a few short term cases where its not) trying to run the engine as close to the point of knock as possible e.g. if you instantly cut the fuel supply between 2 tanks of 95 & 98 ron it would more or less instantly adjust -- but as ken says, it's the mixing of the 2 versions that's the real issue, until you've gotten rid of the 95 ron in the tank.

I'm 100% convinced of the need for additives to our fuel, given the stress levels required of modern injectors to do their jobs. Whether that comes from always buying a fuel with a known additive package (do we really know what's in the additives or how much is present, other than anecdotally with the likes of shell & BP ?) or buying a tin of additive every few months and putting that in with straight normal fuel from any source.

The TSI engines are designed to run fine (at full power) on 95 octane fuel and can run on as low as 91 Octane. They have a knock sensor which detects if the fuel is of poor quality and then Engine Management Unit then retards the ignition by a degree or two to preventing the knocking.

95 should be fine most of the time, occasional use of Shell etc is generally thought a good idea because of superior additives in their fuel. Also use of 98 might be advised if you were fully loaded ie 5 people, boot full of stuff and it was hot summer day or to use on a track day. Our TSI VRS seems fine on 95 Octane but we will lob in the occasional (1 in 4 maybe) 99 Octane as it get mixed very quickly by the fuel system and will compensate if one does get a below par batch but the engine is cleaver anyways so I suggest you mix supermarket and direct oil company purchases. If remapped of course different story, highest octane obtainable.

lol

Yeah I've been reading up on all the posts re: supermarket fuel vs Shell etc, and indeed what people have been saying about different supermarkets, to try and get a feel for the general feeling of the better places to fill up. Since getting the car, I've so far avoided where I always used to fill up with my old car (Asda, as that's usually cheapest) - and will be trying more to fill up at somewhere like Shell whenever I can if it's viable. Difficult to know definitively what the situation is for like-for-like petrol re: e.g. Asda vs Sainsburys vs Shell vs Esso etc etc

Under "really extreme" load; we're talking 4 people plus a caravan type loads here; a couple of points extra octane over what is normally required by the ignition map/curve can be an easy way out of pre-ignition (or extra advance which loses you the power when you need it most).

In the "Owner's Manual" there is a line saying something like:

"You can use higher octane fuel (higher than 95) but you will gain nothing."

Those are not the exact words but reflects exactly the meaning.

The higher octane fuel (98) only makes the difference for cars that require it. Not sure if the VRS requires it. Otherwise it is worth nothing,just psicologic gains for the customer, higher profits for the oil companies though.

I would never use 98 unless no other option in the petrol station and my tank is empty.

There is no difference mixing 95 and 98 if your car does not require 98.

In the "Owner's Manual" there is a line saying something like:

"You can use higher octane fuel (higher than 95) but you will gain nothing."

Those are not the exact words but reflects exactly the meaning.

The higher octane fuel (98) only makes the difference for cars that require it. Not sure if the VRS requires it. Otherwise it is worth nothing,just psicologic gains for the customer, higher profits for the oil companies though.

I would never use 98 unless no other option in the petrol station and my tank is empty.

There is no difference mixing 95 and 98 if your car does not require 98.

When you say difference do you mean no power difference or just that the you are unlikely to notice the difference?

For our sins we tend to use Tescos fuel because it is cheapest and we get heaps of pay back vouchers from them but they have historically bought the fuel direct from Rotterdam and of questionable quality ie issues with impurities a year or 2 ago. We have been running our VRS in so there are some higher internal tempurates during this period so have dogged in a tankful of 99 octane just to be safe but probably will use 95 mostly. VRS produces 100 hp/litre so is quite highly stressed. It will be interesting when the UK gets the Fabia VRS with its 180 hp from 1.4 litre to see what Briskodians reckon to put in that motor.

Edited 9 April, 201016 yr by lol

When you say difference do you mean no power difference or just that the you are unlikely to notice the difference?

For our sins we tend to use Tescos fuel becuse it is cheapest and we get heaps of pay back vouchers from them but they have historically bought the fuel direct from Rotterdam and of questionable quality ie issues with impurities a year or 2 ago. We have been running our VRS in so there are some higher internal tempurates during this period so have dogged in a tankful of 99 octane just to be safe but probably will use 95 mostly. VRS produces 100 hp/litre so is quite highly stressed. It will be interesting when the UK gets the Fabia VRS with its 180 hp from 1.4 litre to see what Briskodians reckon to put in that motor.

Well, directly from the wikipedia "The octane rating is a measure of the resistance of petrol and other fuels to autoignition in spark-ignition internal combustion engines." (you can find it here).

This means that one RON98 fuel is not more powerful than a RON91 fuel, it is just more "stable".

The engines internal compression is what results in the need of a higher octane fuel or not.

For example if my engine requires RON95 this means that this fuel will be stable enough for exploding when the spark starts and not while it is compressed in the cylinder.

A lesser octane fuel would ignite in a not appropiate moment making the engine run worst, losing performance, and requiring more fuel to get the same power, more pollution...

A higher octane fuel will ignite at the same moment as the RON95 fuel so no more power, no more MPG no more nothing, just less money in our pockets.

Of course if a fuel is bad quality then we have to directly avoid it just ignoring if it is 91,95 or 1000 octane

Hope this helps.

Mine's weirder still. Inside the petrol flap it says Min 95 Ron but then says Super Unleaded (in several places and languages on the label).

We don't seem to have any 98 around here - either 95 regular unleaded or 97 super. Only Tesco offers anything else - their Super is 99.

On my fuel cap it states 98 RON, so I feed it either Shell V-Power or Tesco Super 99 RON.

I don't do galaxy mileage so the price premium over 95 RON fuel doesn't bother me too much.

Tesco Super 99 RON is cheaper than V-Power where I live at the moment. Usually the other way round.

The Tesco stuff is made by a company called Greenergy:

http://www.greenergy.com/tesco_99_octane/index.html

When I first got the car I stuck a couple of tanks of 95 RON. Then decided to use super unleaded and noticed much better MPG, responsiveness and smoother idle.

Decided to stick with the super unleaded as it also contains additives that keep the engine clean and healthy.

im a great lover of super unleaded ive used in my last 5 cars, there isnt always more power but the car always always runs smoother no pinking or knocking+ the additives keep your engine cleaner.

WATCH this video for non believers

, its the golf gti but its the same engine!

ive always found shell v power to be the best bar none, but lately ive been using sainsburys 97 and ive been very impressed with it

Edited 9 April, 201016 yr by furn

On my fuel cap it states 98 RON, so I feed it either Shell V-Power or Tesco Super 99 RON.

I don't do galaxy mileage so the price premium over 95 RON fuel doesn't bother me too much.

Tesco Super 99 RON is cheaper than V-Power where I live at the moment. Usually the other way round.

The Tesco stuff is made by a company called Greenergy:

http://www.greenergy.com/tesco_99_octane/index.html

When I first got the car I stuck a couple of tanks of 95 RON. Then decided to use super unleaded and noticed much better MPG, responsiveness and smoother idle.

Decided to stick with the super unleaded as it also contains additives that keep the engine clean and healthy.

I have swapped to 98 ron in my Elegance 2.0 FSI and like you have found it smoother, even though it is mixed with about a quarter tank of 95. Ruinously expensive though!!

Mine's weirder still. Inside the petrol flap it says Min 95 Ron but then says Super Unleaded (in several places and languages on the label).

We don't seem to have any 98 around here - either 95 regular unleaded or 97 super. Only Tesco offers anything else - their Super is 99.

Ignore the term "super" - in most other european countries 95ron is the higher rated fuel, hence it's superunleaded. You only need 95ron in the TSi engines.