Technical Optimax

[Neil Barker]

I have a Stilo Abarth and today decided to fill it up with Shell Optimax to see what, if anything, happened. OK, it had approx 1/8th tank of normal 95 RON unleaded in there when it was filled up, so it won't be 'neat' Optimax.

After approx. 20 miles driving, I parked my car and came back to it a few hours later.

I then drove off, down country lanes, to see if I could begin to detect any improvement.

Well, err, not exactly - this may be totally co-incidental with something else, but my engine's performance at the top-end has dropped off and when accelerating hard, it feels what I can only describe as 'strained' - it doesn't sound the same, either. It almost feels like the engine is misfiring at high revs, producing a drop-off in power.

I can only put this down to one or more of the following:-

1) My engine doesn't like the unleaded/Optimax mix - which
would eventually improve as it becomes neat Optimax with
successive fill-ups. Perhaps the ECU is confused ?

2) I have something wrong with my car which is causing this.

I was concerned, so I called out the AA - he'd never seen a Stilo Abarth before and took it for a short test-drive to see if he could detect anything. He remarked on how quick the car seemed, but given that he'd never driven one before, he had nothing to compare it against. He checked my car's computer with his laptop and found no error codes.

I took my Stilo for an Italian tune-up for 40 miles (as much also to burn off the Optimax) and it doesn't have the performance it used to - when accelerating from 70MPH, it would rapidly go past 100 and keep pulling. Now it feels like it's hard work.

I'm puzzled as to just what to do here.



--
Neil Barker

 

[Idge]

Hello Neil,
I have a 1.6 Dynamic, and my last fill up (almost from empty) was a tank of Optimax. I was hoping it may help me out with a non-specific running problem that I feel I'm having, in that sometimes when the car is fully warmed up, if feels sluggish under acceleration, and the exhaust gets a 'boomy' tone, which isn't there a lot of the time. It is hard to notice a problem unless you drive the car all the time, and even though I'll book it in, I imagine it'll be the old 'the computer says its OK so it is OK' routine which seems to effect most dealers these days.
Anyway, back to the Optimax, I was hoping it would remove these flat-spots and run 'smoother' as it has in friends' cars, but I've used three quarters of a tank which was filled almost completely with Optimax, and to be honest, I can't feel any difference whatsoever in performance. To be honest, still being quite new, I don't give my car the thrashing many people do, so I couldn't tell you about high-end response, but I was hoping it'd help the overall running, which it hasn't. If I remember rightly, the manual says to use 95 RON, and dosen't mention the use of higher-octane petrol, while other people's cars say better performance will be had with 98 RON etc., so maybe Stilos are engineered to use 95 RON and nothing else, who knows? I'll be going back to standard grade once this tank has run down a bit more, as I can't see the use in splashing out more for the Optimax.
Is anyone else having problems like me (especially the 1.6 engine?)

Best wishes.


2003 1.6 Dynamic 3 Door - Tiziano Red

 

[Scorg]

Being new to the Stilo im not fully up on its engine but if it does not have a Knock sensor in it then it wont be able to make use of the higher octane fual.
Being a Rover owner also this subjects been gone into great detail on a Rover forum. Whats been said with its K series engine, which does not have a Knock sensor and designed for 95 octain. is it makes the car a bit more fual efficient while not gaining anything from performance.
This could well be the case with the Stilo engine range also, altough it running rougher does sound odd.

Our Stilo is also the 1.6 Dynamic but we've only had it since Wednesday and so far the engines running lovely, Very smoove and very responcive, Makes a massive difference from the 1.6 we had in the old Tempra (which was very flat spotted and even near lost throttle control under exteme rain conditions)

Regards
Andrew

 

[dutchdee]

Optimax doesn't quite work as well on new cars as it does on "older" cars. The way new engines are designed already extract the most power they can from unleaded as they are (untill moddified)and using a higher octane rated fuel gives ,if anything, a slight increase in mpg rather than better performance. I found that in my 1.6 active sport it gave approx 40 more miles to a full tank than 95 octane petrol with no noticable power gain, yet in my 1995 Astra 2.0i 16v it gives 14bhp more at the wheels. Does the extra cost of optimax compensate for getting 40 miles more to a tank... Personally, I dont think so.