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I used to use pre-Optimax Super-unleaded Shell in a T4 saloon and found there was a clear improvement in power, smoothness, reduction of turbo lag (not a great problem anyway)and a slight decrease, maybe 2 mpg, in fuel consumption. I now have a T5 coupe using Optimax and the same applies but to a lesser extent. Is it the case that Optimax is a half way solution between the old Super and the Premium?
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Is there a diesel equivalent to Optimax?
I remember using Optimax in my old Volvo 340 and getting about 42mpg out of it on a fast motorway cruise (which was about 6-8 mpg better than I normally got)
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If you search the old site you will see loads of threads on Optimax. My impression was that the majority did not think it worth while. There was also a warning that it might have been withdrawn from sale in Europe; but I don\'t think it was confirmed.
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Clarkson advertises it, so it must be good - must it?
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I hate to be controversial on this site now that it has become such a friendly place to visit. However I suspect that any claimed differences in mpg between Optimax and any other comparable fuel of the same octane rating would not be supported in scientifically conducted tests. I may be wrong in this belief but I've yet to see proof of such claims. I often use Optimax in the BMW and the old Triumph because that is what the local garage sells, but I also use the cheapest fuel available when out of town so I don't have any particular bias towards or against Optimax.
Reminds me of the introduction of Jet petrol in 1960-ish, which undercut other makes at the pumps. There were claims that Jet kept the price low by having a lower octane rating than the others, at the bottom end of the permitted tolerance, and this was affecting economy and/or performance. In fact, I understand that the octane rating of Jet was kept slightly ABOVE the norm to absolutely ensure that they were never caught out in tests because they knew this would be likely to put them out of business.
Until a new and more scientific system for determining the octane rating was devised by a team at London University within the past decade or so, the only practical method of determining octane rating was to feed it to a special engine (of a very old design) in a test rig. The results could be so variable that it was normal for refiners to aim a bit high, to ensure compliance with the permitted rating 'spread' for the grade of petrol under test(eg.two-star, four-star) but Jet went a bit higher still for the reasons given above.
It may well be that the old system is still used by the oil companies - I'm no longer in touch with these things. Does any Backroomer know?
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Slightly tangential, but I heard on R4 last week that Shell were funding research into ethanol production from biomass (posh term for stuff that grows) with a view to putting it in petrol, which generally improves combustion and cleanliness (Cleveland Discol, anyone?).
This was being touted as a great development, but I seem to remember the same combination being marketed as 'Gasohol' in the US in the 70's. Presumably it failed there because it wasn't helping oil company profits...
What goes around comes around.
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JBJ
Yes, I remeber the Cleveland Discol ads. 'Aromatics boost performance' was it not?
Regards
John S
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It was something like that. It disappeared from the forecourts not long after I started motoring, but I did use it a few times and it did seem to work better. I think it had about 5% alcohol, but gasohol has/had something like 20-30%, which is about as much as you can add without requiring adjustment to the fuel/air ratio. It is supposed to burn much more cleanly, both in terms of emissions and combustion chamber deposits, so I'm not at all clear why it isn't universally available unless, of course, the oil companies feel threatened by it.
I vividly remember once looking down the bores of a methanol-fuelled Chrysler Hemi V8 and seeing no carbon deposits whatsoever...
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Has Which? or similar, ever done any analysis of fuel by brand?
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I ran my Bora for a month on Optimax and there was no noticable difference other than the increased cost !
I've just searched the Which Online web site and it doesn't look like they've ever done that sort of test
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Mpg went down slightly on my mk2 Golf GTI, probably because I thought I should get a bit more 'performance'. Couldn't tell the difference oomph-wise though.
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What you buy out of a Shell or Bp pump may not necessarily be refined by them-all it has to do is meet the minimum-repeat minimum-requirements for it to be legal for sale.
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HJ,
Tried following your link to millersoild.co.uk but could not find the site. Is address correct, or is it me?
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Dizzy
I agree with you. An engine converts the heat energy in fuel into mechanical energy. The heat content of all petrol is to all intents and purposes the same and has nothing to do with octane rating. The higher octane rating allows suitable designed engines to operate slightly more efficiently, so making better use of the fuel. Effectively petrols with higher octane ratings exhibit slower combustion, so reducing risk of detonation.
Therefore only engines with an engine management system and knock control which can take advantage of the higher octane fuel could possibly benefit. I believe even these will probably only see the benefit in terms of power when the engine is being pushed hard, as detonation isn't a problem when running gently.
It seems unlikely that this fuel is diferent enough to give major economy benefits, especially in engines not able to adjust themselves to use the octane rating. Last time I looked at Optimax prices I'd have needed 10 - 15% improvement in fuel consumption, and I don't think that's likely.
Regards
John S
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