For those with way too much time, this is really useful information:

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

I actually understood half of it, and it only took me 4 hours to read...

FWIW my car is "tuned" to our SUL (98 RON), used Optimax for an Elvington trackday in July, and saw no problems at all KnockLink-wise or power wise. DeltaDash afterwards showed nothing unusual. Car was running OK, despite me being a bit paranoid after all the threads about this so far. (circumstantial evidence)

Edit to add a pretty relevant quote:


In the late 1960s German automakers discovered their engines were destroying themselves on long Autobahn runs, even though the Research Octane was within specification. They discovered that either the MON or the Sensitivity ( the numerical difference between the RON and MON numbers ) also had to be specified. Today
it is accepted that no one octane rating covers all use. In fact, during 1994, there have been increasing concerns in Europe about the high Sensitivity of some commercially-available unleaded fuels.



[Edited by EvilBevel - 11/6/2002 5:32:07 PM]

 

Had my first year service at the weekend, and they recommend that I don't use Optimax as frequently as I have been. (Every fill up) Do Shell do Super unleaded petrol or is it just BP?
I'm going to start using 1 out of 4 with Optimax instead.

 

Shell don't do Super, only Optimax.

Did they give a reason?

 

Did they say why you shouldn't use optimax the whole time? I was told by my dealer to use it. IMO there is not noticable difference between Optimax and SUL in any case.

Charlie.

 

They said that the Optimax tends to clog everything up with continued use, and that the Super unleaded will clear this out.
I'll give it a try and see.
There have been posts before about Optimax and losing performance, but when I changed to BP's SUL I thought the car felt very sluggish. I'll have to give it a test over a month or so.

 

But when Evo did a test running some cars on Optimax it was proved that it cleaned the engines of deposits left my other fuels...

 

because the ECU adapts itself depending on the RON of the fuel you use my dealer told me to always use the same fuel (where possible) rather than 3 Super, 1 Optimax as you're planning.

I always use Super as there's no shell garages near enough. Have used Optimax once and liked it but not that much greater than Superplus. I think the only differences I noticed (a little smoother) were probably psychological cos I was expecting it to bebetter. When I went back down to 97 on the next tank I didn't notice any different.

 

Optimax is more tempramental than other SUL-type fuels.
There are additives in Optimax that clean the engine. Use it all the time, and the additives start to coat everything (look at the exhaust bit of a turbo from a car that has been run on additives & you can see the orange stuff all over it!) but I can't really see causing any problems... I have that there have been problems on one or two other engines, but that has been because of an effective fault with the engine design.
But if the garage you fill up with Optimax from has a low turnover, it may be better to stick to BP/Esso, etc.!

 

Nom and others make some good points.

I lost an engine after 11,000m exclusively on Optimax which probably had absolutely nothing to do with the fuel.

HOWEVER I have used mainly BP/Esso/Texaco SUL since and occasionally Optimax. I've definitely found that SUL is more consistent than Optimax in the 6000m since.

Also call me Mr Paranoia but remember 'Formula Shell' back in the 80's ?

 

No, I don't: I was still in primary school: care to fill me in?

 

My 93 wrx runs very well on optimax and pretty crap (rough) on anything else. I also run with broquets. Just my two pence worth.

 

I will give it a test on SUL over a month or so and post my results. I started to build up a good few points with Shell aswell. What kind of rewards scheme does BP do?

 

BP used to do Argos Premierpoints, but now they're part of the Nectar scheme with Sainsbury and Braclaycard.

I too was in primary school in the 80's. What is this about 'Formula Shell'

 

i used to run super and octane booster, switched to optimax, noticed no difference but its easier than super and booster
mark

 

One thing not answered from the original post. Shell don't do SUL, but it's not just BP that do either. ESSO certainly do, Q8 do at some stations, and I believe one or two others do as well, but not at all their stations.

John Banks stated that you get away with more ignitiion advance using Optimax, and I tend to find I get perhaps 1mpg better economy with it. However, if anything, my car feels better on SUL. Already been a lot of debate on it, and will no doubt continue to be.

 

Forgive me for bringing this up again but i have found on average about 1mpg *less* with optimax as compared to BP or Esso SUL. No idea as to why this should be. Like I said, I have not been able to discern any advantage to optimax over SUL, but it is usually around the same price so I carry on using it.

 

Glad its not just me who knows their car feels better on SUL rather than Optimax (over several '000 miles, not just the odd tank).

RE: Formula Shell - nothing like Optimax, but made great claims for
its engine cleaning properties ... but also the need to replace bits of your engine, especially if you drove a Vauxhall. Was subsequently withdrawn, but Shell said there was nothing wrong with it.



[Edited by Flat 4x4 - 10/21/2002 9:33:50 PM]

 

I find switching between SUL and Optimax gives the best results

Subaru dealer warned me to stay away from Optimax as they had seen loads of problems with owners cars thet were exclusively run on Optimax.... but I can't be bothered going into this all again, as it really has been done to death

 

I would be interested to know why they are saying a better fuel can damage the car ?
I run my car on optimax so if I can understand the logic behind thier reasoning I will have to change to SUL.
correct me if I am wrong but surely it should either be one or the other as this mixing **** is a waste of time as the ECU's on older cars take a while to adapt to the fuel so thats would really foof em up. Had my say.

[Edited by scrappy_doo - 10/22/2002 11:51:35 AM]

 

Optimax uses additives - more so than other 'supers'. Additives can, in excess, cause problems. Usually there's no problem for the manufacturers, because the additives are 'user' additives; the ones in Optimax are very similar to those used, but they are part of the fuel.
Particularly nasty things can happen if you add additivies to Optimax, as the chemicals can clash!
But I suspect this is all caution on behalf of the manufacturers, as opposed to based on fact - for the moment at least (or at least the Optimax on its own bit!).
Also note that as Optimax is more prone to degrading than other 'supers' (fact), the RON can/will vary, possibly down to & below that of the average SUL.

 

Optimax is generally sold in much higher quantities than SuperUnleaded, so it is more likely to be "fresh" than SUL.
It is also manufactured as a whole product, whereas SUL is normally basic UL with octane booster and additives mixed in as it goes into the tanker. Since basic UL is refined all over the place it is subject to considerable variation. IMO Optimax is therefore a more consistent product.
(...and it does have a higher octane rating )

 

used optimax when it first came out found car lacked performance ,was told to keep useing it and things would get better, not the case ,changed back to esso last week car took few days to pick up but it now back to its old self going superb on esso sul , so i would agree with most people that optimax in scoobs is ****
shocker

 

Well, it's the other way round (Optimax is 95 with additives, which is why it's cheaper - it slots into NUL the tax bracket), but there you go - can't have everything

 

Mine runs PANTS on Optimax when run from cold. Ran it like this for months thinking the hesitation was plugs or mixture.

Changing to SUL cured it immediately

 

I have run optimax since it came out....running much higher boost than normal on a UK car...never any problems that hadn't been cured by new plugs & coilpacks, air induction, cleaning the MAF & boost pipes etc.

That wasn't a direct dig at the reply above btw, fair comment for you it worked changing to SUL.

shunty

 

So how many people use SUL, How many use Optimax, and how many mix the two or use something else?

 

I have been tempted a few times to fill up with SUL & swap for a bit...but mine runs superb on Optimax so no point really.

shunty

 

I thought mine was running OK on Optimax, but I don't like the thought that regular use could be damaging something.

 

I wonder if it's related to the year of scoob....
interested to see if any of the pre 97 scoobs have any probs with optimax ??
just a thought, it's prob been covered already though.

shunty

 

It's most likely to be a problem with where you fill up.
There is a noticeable difference between different garages - my 'local' is not good (it will be in a low-turnover one from where it is), whereas the one 'up the road' (the M1) - high turnover - was immediately and obviously in a different league altogether. The M1 stuff was far better than 'normal' SUL, the stuff from my 'local' I'd say a little worse.
Cars with newer ECUs will obviously be better off as they are able to constantly adjust to the fuel mixture - I imagine, as normal SUL seems to be more consistent, that it would suit older ECUs better.
But this is all IMHO of course