Optimax

Strange that. In both of the petrol vauxhalls I've owned the tope end is where the greatest (subjective) improvement was.

If you find optimax is worse, then fill it up with normal petrol in future. You won't have done any harm so just continue using the car and don't worry. Mixing is harmless too. I did find that in both cases that after changing fuel type it took up to 200 miles to settle down, presumably learning the new setting required.

The Dervboy.

I have noticed this too. Put some Optimax in my CDi Cavalier, and it made an improvement to top end, as well as slightly better average fuel consumption.

Put some Optimax in my Suzuki GSXR750. A mistake! It seems to run rougher and seems to pink more readily than before. Put standard unleaded (BP) in, and all is back to normal. Phew!

Anthony Remove eight from email to reply.

Most of the mechanical rattling from my old GSX600 was from the camchain. Never could quieten the thing down. Sorted it in the end though - changed it for a GSXR600! What a difference...!

Anthony Remove eight from email to reply.

My GSX600f did the same. Full throttle from 8k and pinkpinkpink. Full throttle from 8k in top and it made strained farty noises!. Tickover was rougher and it vibrated far more noticeably. Oil cooled GSX engines are mechanically loud anyway, so to hear it over the normal cacophony was quite concerning.

Standard unleaded at the next fill, 10 miles later and all was sweetness and light.

On older Fiats the ECU has intuitive learning, i.e. it adapts to your driving style etc. I know on older Fiats that this can be reset by disconnecting the battery for 10 minutes or so. Alternatively put up with it and eventually over time the ECU will re-learn the best settings.

Andy

Well, it could be a co-incidence.

However, we've a chap with a Duratec-powered Ka (the newer 70 PS engine) who says that although his Ka seems to pick up better, top speed is reduced (!) when running on Optimax.

We're at a loss to explain. When running Kermit on the stuff, it behaved just as I'd expect if I were running injector cleaner through a diesel . . . picks up better, a bit quieter, some improvement in fuel economy but not much.

Surely any ECU adapts to your 'driving style' ie throttle input and the revs you take the engine to? Not much point in it if it didn't. Are you confusing it with an auto gearbox ECU that *can* learn from driving style?

My car's top speed and overall performance is reduced when running on Optimax as it is now. I'm just waiting for that happy moment in about 90 miles time when my tank's empty so I can fill up with good 'ole 95 RON unleaded again.

Never have I been so eager to see my fuel tank empty !

Higher-octane fuel is, by its very nature, slower burning than ordinary RON

1. It could be possible, in some cars, to find that combustion is not complete at the end of the exhaust stroke and the fuel explodes in the exhaust manifold making a pinking-like noise. So ironically, if putting higher-octane fuel in the car to try and stop pinking, you could end up making it worse.

That's rather different to 'driving style' and again surely is a function of most new, rather than old, cars.

adjust

fuel

is a function

You said 'any ECU'. Most I believe, are simply pre-programmed, and the settings don't change no matter how it's driven, but I don't think most new cars _are_ fitted with knock sensors, or have an ECU with an adaptive learning capability. As I understand it, those that can, do adjust according to driving style, and the car needs to be driven hard sometimes for the ECU to 'learn' all the settings that may be needed. IOW if you drive sedately, and never use maximum acceleration or drive the car hard, the settings will remain at the optimum for that driving style. On those engines with a knock sensor, when a knock is sensed, the ECU retards the ign timing slightly, and continues to do so until maximum advance without knocking is reached, It then 'remembers' that setting, until something changes, or it's reset or a different octane fuel is used. Mike.

I've not known *any* car to run worse on higher octane petrol - even my pre war Austin 7 on 5 star at 100 octane when it was designed to run on around 80. It doesn't make any sense. Do you get the same effect with BP Super?

Complete new engine and cooling system.

My car was off the road for 1 day short of a month to solve the whole sorry affair. It took two weeks to get an engine from Fiat :-(

Great car. Shite dealers and backup.

My engine runs better with Optimax, there is increased power and better economy when the engine is under load (stop/start driving - in town or across country) but not on a motorway run. The effect is almost immediate after filling up, it just has to clear the old fuel out of the pipes. The ECU reacts quickly to the knock sensors and there isn't really any learning time.

However I did fill up with Optimax once and the engine ran worse than with unleaded. When I came back from my trip I noticed that the fuel station I filled up at was closed so I put it down to contamination/bad fuel and the next tank of Optimax was as good as ever.

I'd suggest trying one more tank full from somewhere else after a tank of unleaded (just to make sure that an engine fault hasn't coincidentally developed).

once popped optimax into a pug hire car and a short while after the engine fault lightcame on and the enge went into the "get you home" mode...

i carped myself, but turned out to be coincidental, a sensor failure!

Roughly the same experience with a Galaxy V6 (i.e. with the VW VR6,

On standard UL95 I was getting 26.8mpg according to the trip 'puter.

After switching to Optimax on an empty tank I'm getting about an average of 28.6mpg after about 300 miles of similar mixed driving. The test/trial of Optimax continues for a little longer...

Doing the sums with the 6p/litre price premium the MPG gain isn't worth the extra price, especially with a wider choice of discounted UL95 around (e.g Sainsbury's with a money-off voucher).

As for running/performance I haven't noticed much open-road difference, low-end acceleration seems marginally better. Again, not worth the price premium IMHO.

I hear exactly what you're saying - I understand about timing/octane ratings etc.

I managed to run my tank as dry as possible this afternoon and then filled up with normal 95 RON unleaded. After a few miles to get the new fuel flowing properly, I'm pleased to say that the car now behaves almost as it was doing pre-Optimax - it pulls strongly and doesn't sound like it's sometimes misfiring as it did with Optimax.

Evidently my car simply doesn't like the stuff !

Higher-octane fuel is, by its very nature, slower burning than ordinary RON

1. It could be possible, in some cars, to find that combustion is not complete at the end of the exhaust stroke and the fuel explodes in the exhaust manifold making a pinking-like noise. So ironically, if putting higher-octane fuel in the car to try and stop pinking, you could end up making it worse.

That's the theory, but any car with this sort of hairy valve duration is likely also to have a high compression ratio.