Reduced fuel economy when using 99 fuel compared to 95

[piggoy]

Seems a little odd this one - Most people on here report increases in fuel economy when using high octane fuels; they say that high octane fuel costs more but the extra cost is balanced by the increased MPG.

I've found quite the opposite. My normal journey to work and back is about 25 miles on mostly dual carriage way roads. I normally drive between 70 and 80 ish. I tested 1000 miles on Tesco 95 fuel with a recorded average of 37 mpg. 1000 miles on Tesco 99 fuel averaged at 32 mpg :S WTF?

I'd be quite interested to get the opinion of some ECU experts. This doesn't seem normal to me. I know that ECUs take a while to switch between fuels but 1000 miles should be sufficient.

 

[JonC]

Simple, Tesco 99 is blended with ethanol which whilst raises the octane rating, actually gives less "bang" per volume of petrol. Octane is not a measure of energy released but measure of controlled burn.

 

[piggoy]

Point understood - But in engines with higher compression ratios which are designed to burn high octane fuels I presume that you get more efficient combustion due to ignition under higher compression, and therefore better overall efficiency in terms of energy released per litre of fuel? If you don't get more bang for your buck then what's the point? The car runs perfectly well on 95 which is considerably cheaper per mile.

 

[blackpanther]

Found this myself, ran the high octane for about 6 months then switched to normal 95 and found not only better mpg but no degrade in performance. Ive always used 95 ron since.
(i do only use shell, never ever used anything else)

 

[TimR26]

Tesco 99 is rubbish for fuel economy and I found it made my car sound louder. V-Power is much better IMO

 

[Dunn]

v-power gives me almost instantaneous more MPG compared to 95 ron always

 

[piggoy]

Quote from Lord Fred@BTM "tesco 99 has 5% bioethanol which is good for power, not as efficient for mpg" - I'll believe him

 

[piggoy]

Fred@BTM "...you are wasting your cash on a clio running anything more than 95, the end"

 

[franx]

Mine does'nt like anything lower than RON98 ! Can very easily tell the difference. I do'nt care about the MPG though, just the performance

 

[jinjur]

Mine does'nt like anything lower than RON98 ! Can very easily tell the difference. I do'nt care about the MPG though, just the performance

Agreed, miswah is running my 172 at the mo and filled it up with Sanitarys SUL yesterday but didnt tell me.

I was out in it last night and thought is was idling so much better, much less lumpiness.......more eager to rev too. There was me sitting trying to work out what i had done the night before to make it feel so much better.

She just happened to tell me later on that night she remember to use SUL.

So i dont think it was the placebo effect

Jj

 

[J.B.]

Interesting. I use Tesco 99 and I'm now wondering if it's part of the reason for my lumpy idle. Is Sainsburys petrol any good or should I just use Shell?

 

[Pedro]

Well theres somethig wrong with mine and ill ask Fred about it later.

I run mine on V-Power and although im being pretty sensible im only getting 28mpg...

 

[mat-nos]

mine seems to run better from cold with high octaine but imo no difference after that, so i now save my money and put up witha jerky first 5 mins with 95ron....