Shell Optimax bizzare fuel consumption

[sportquattro]

OK this is a bit of a puzzler, for past few months have been running my 1999 S3 on Shell Optimax and Tesco 99RON, and my fuel consumption has gone from 360-400 Miles per tankful to 310-340 miles per tankful. I recently replaced my MAF as it was showing a low 170g/s and after changing it went back to 205g/s and the economy returned. my immdiate thought was ah it's the MAF thats been killing the economy, however, on the following three tankful things were back to 310-340 mile per tank. I have now discovered that the tankful I bought after replacig the MAF was when Shell had a shortage of Optimax and I remember putting in normal unleaded as I was needing fuel badly, the next 3 tankfuls were Optimax, last week I went for fuel and saw the price, and stuck in normal Shell unleaded, and low and behold my economy has returned, I've run two more normal unleaded tankfuls and got 365 and 379miles out of them. I can only therefore deduce that for some odd reason my S3 runs better on the cheap stuff. performance seems as good as ever judging by the "seat of the pants dyno" yet im definately getting better MPG. I drive very similar miles and routes each week so its not a case of different conditons affecting economy.

I'm going to stick with normal unleaded, but am curious if any of the experts on A-SN have any theories. Logically it should be better on Optimax but its not.

Nige

 

[<tuffty/>]

First port of call is to look for any fault codes then it would be some logging to see whats going on using VAGCOM... assuming you have access to this as you have checked your airflow...

First thought is Lambda, have you done anything else to the engine like an N249 bypass etc?

Still pretty good consumption all things considered, motorway mileage?

Curious one...

<tuffty/>

 

[1animal1]

erm, i get roughly 250-300 miles per tank before the light comes on......think your still fine all things considered

 

[jojo]

erm, i get roughly 250-300 miles per tank before the light comes on......think your still fine all things considered

Yes, this sound like my car, anything over 300mile per tank is not using the car to it's full potential.

 

[martin g]

Hmmm, u lot have heavy feet!! i also get 375 as an average....my best is 390..and i have photographic proof //hahah

 

[sportquattro]

First port of call is to look for any fault codes then it would be some logging to see whats going on using VAGCOM... assuming you have access to this as you have checked your airflow...

First thought is Lambda, have you done anything else to the engine like an N249 bypass etc?

Still pretty good consumption all things considered, motorway mileage?

Curious one...

<tuffty/>

Hi Tufty

I have run Vag-Com and no fault codes are showing, the only things done recently are fit a Forge 007P and the new MAF as I say the car runs fine, is certainly not lacking in go at all, it's just appreciably more economical on normal unleaded than Shell Optimax superdouper wizzo wonder juice. Driving is a mix of local and motorway miles with a good amount of "fun" along the way. I'm doing about 400 miles a week so I'm going to continue with normal unleaded on the basis that it seems to go further on a tankful and its about 5p a liter less extortionate with no obvious (to me anyway) drop in perfromance.

Thanks
Nige

 

[fingermouse]

i used to get 330 on original wheels, now im on 19`s and 235 wide then average is 300 miles per tank doesn`t seem to matter how I drive her lol

 

[S3quatt]

I doubt if it actually has a problem, I calculated the mpg differences between ordinary & optimax when i had my S4, & it always got better MPG on the ordinary fuel.

The advert IMO is false advertising!

 

[DaveA3]

i got 48.4mpg on the motorway (120 odd miles)

only a 1.8t 150 tho.

i seem to get better fuel return on the normal stuff aswell. tesco 99 runs best but doesnt last as long. very strange indeed. i thought it was supposed to last longer?

 

[s3dave]

could it be the fact you are putting less in as optimax is dearer so £50 worth you would get a lot less?

 

[sportquattro]

could it be the fact you are putting less in as optimax is dearer so £50 worth you would get a lot less?

Hi S3Dave, no i always run the car down to the low fuel light then with 10-15 mile remining get fuel and top her to full its near as damnit the same amount each time in quantity of fuel it just goes further on normal unleaded.

Nige

 

[DaveA3]

i did think that at first but put exactly 30litres in with both fuel and the normal still out performed it very strange!

 

[lee111s]

250 miles per fill up here