95 or 98 petrol - what do you use?

[theresanothersteve]

I know this is not part of the OP original Q, but has anyone used Unleaded 91 in a new 17/18 Tiguan with no reported issues ?

Don't do it. Just don't.
Many of the reliability issues with the twincharged motor came about because people were using 91RON.
If you use 91 there is an increased chance of detonation or preignition. It's not like an old red motor Holden that, if it started pininging, you'd call in the local servo and a mechanic would check your timing (yes, I'm that old). You might not even be aware its happening as the ECU tries to accommodate the fuel. But it's doing damage inside the motor.
Why buy a vehicle because it offers good, smooth performance, and compromise on that to save a few cents a litre?

[FastMitch]

Don't do it. Just don't.
Many of the reliability issues with the twincharged motor came about because people were using 91RON.

I didn't know people had been using 91RON in the new 17/18 Tiguan and had reported issues

Thanks for letting me know

[ewok666]

I didn't know people had been using 91RON in the new 17/18 Tiguan and had reported issues

Thanks for letting me know

Why would anyone use 91 when it clearly states in needs 95? Over the course of 100,000km that's a potential saving of no more than $1500 and a good chance the engine takes a hit. And when it does there's a very good chance they'll deny the warranty claim. Surely they can tell from the ECU logs that the engine was constantly running **** fuel.

[FastMitch]

Why would anyone use 91 when it clearly states in needs 95? Over the course of 100,000km that's a potential saving of no more than $1500

Baseline:
91RON Fuel Price: $1.42
95RON Fuel Price: $1.59
Assume 10l/100km (efficiency from all city driving)

Equates to a saving of $170 per year if you avg 10,000 km per year

[prise]

Many of the reliability issues with the twincharged motor came about because people were using 91RON.

What's your source on this? I had two work colleagues, one with a Jetta and one with a Golf. Both ended up with a check engine light, rough running and a diagnosis of cracked pistons. They did not use 91 octane fuel.

The dual charger engines were notorious for the pistons cracking in the ring land area and this occur in markets (eg UK) where 95 octane fuel is default.

[theresanothersteve]

What's your source on this? I had two work colleagues, one with a Jetta and one with a Golf. Both ended up with a check engine light, rough running and a diagnosis of cracked pistons. They did not use 91 octane fuel.

The dual charger engines were notorious for the pistons cracking in the ring land area and this occur in markets (eg UK) where 95 octane fuel is default.

This, and other forums...

I did a lot of research on the twincharger before I bought one. I love the way they drive, but the media is full of VW horror stories. Not trusting the media I conducted research, including with independent VW specialists and some high performance engine types I know.

Interestingly the first incarnation of the twincharger is much as you describe, but around 2011/ 2012 the stories changed from "I had a twincharger and... " to "I know a bloke who has a twincharger and..."

Most horror stories are Golf/ Jetta related, but the motor was used in other bodies later in its life cycle with nowhere near the number of failures. Can you give me verified examples of this happening after the twincharge motor was upgraded? VW is on the nose with the consumer and people love to tell a bad news story.

And Australians are notorious for buying the cheapest fuel they can, manufacturer specifications be buggered. Just about every story I could verify included "I couldn't get 95", "my wife thought 91 was alright" and so on.

[The_Hawk]

Since about 1999 I have run every car I've owned on 98 (had leaded cars before that). My wife had a habit of putting 91 into our '95 Mazda and '01 Hyundai in the early days but I did some tests in both and showed that both were break even at worse thanks to better fuel consumption figures with higher octane fuel. I also assume that better quality fuel is just better for the engine and that was essentially coming for free. So while I showed that it did cost more to fill the tank, the lower consumption meant you did it (slightly) less often.

What's your source on this? I had two work colleagues, one with a Jetta and one with a Golf. Both ended up with a check engine light, rough running and a diagnosis of cracked pistons. They did not use 91 octane fuel.

My twincharger has run it's entire life on 98 and broke it's piston at 30,000km. They just seem to do that regardless of what you do to them... that said pinging that particular engine due to poor fuel is extra extra not recommended.

[DreamensioN]

For what it's worth... 12yrs ago I did a review on Optimax Extreme (the 100RON fuel from Shell). This was back in 2006. I had a Nissan 200SX with an SR20DET engine, running an Apexi PowerFC aftermarket ECU. I also had the hand controller hooked up to it.

The car had been tuned to run on 98 octane fuel. When Optimax Extreme came out, I ran my tank down as far as I dared with the fuel light on, put in a quarter of a tank of Optimax Extreme, ran that down as far as I dared go, then filled it all the way up to the top.

The hand controller of the PowerFC can report a knock value. Basically this value is how much detonation there is before top dead center. I forget how it calculates it, but basically you don't want anything over 60. 60 doesn't necessarily mean the car is pinging, but as a guide, you want the knock value to be below 60 to be safe.

Under normal driving conditions, I would see values between 15-25. If I really got my foot into the car (think going up a twisty hill, wide open throttle, full boost etc) - I would see peak knock values of 30-40.

When I did the review of Optimax Extreme - I got stuck into the car - full load, wide open throttle etc.
As part of the write up - I took this photo of my boost gauge. This was the peak boost I hit - which is fairly high for that engine at the time.



This was the highest knock value I got.... a whole 7.


The difference that 2 extra RON made was incredible.

Now - granted the VW engine is a lot more technologically advanced, and probably has a wide band O2 sensor. But octane still plays a large role. In my Japanese engine, with old technology and a narrow band O2 sensor, under full load my knock value went from 30-40, down to 0-7. I can only imagine what a difference of 3 (95RON -> 98RON) makes. Let alone if someone was running 91RON in their engine which is designed to take a MINIMUM of 95RON.

And last time I checked... a German engine wasn't the cheapest thing to rebuild either.

[Umai Naa!!]

95RON is still borderline in them, even when they've had the re-flash done on the ECU to knock the edge off the timing.

I'd strongly recommend 98RON only, in TSI motors.

[Ozsko]

95RON is still borderline in them, even when they've had the re-flash done on the ECU to knock the edge off the timing.

I'd strongly recommend 98RON only, in TSI motors.

Why do you say that? Do you know more than VW who design the motor and spec 95? I would be interested in the facts behind the statement. It is like people reckon that 15 thousand km oil changes are too long, again with no proof to back it up. Personally I have never used 95 except on one occasion out in the bush where it was forced on me because where I buy my fuel from they don't have it.