Ok this has REALLY puzzled me and might just be a blip but will keep an eye out. I tend to use Morrisons Petrol a lot as its round the corner from me but have seen a fair number of folk over the years say every now and then chuck in a quality Super Unleaded . I saw a fair amount about Shell V Power but many folk said Tesco's 99 Octane super Unleaded was as good . So today tank was just below a 1/4 full and popped in a full tank of Tesco's Super . Seemed a bit sluggish for a couple of miles then have to say it did feel a little more responsive (Could also be the new air filter i popped in start of the week as i believed really you wont notice an engine improvement that quick,usually takes at least a tank or two).

Now i filled it to the top and usually as soon as i start the petrol gauge goes straight to full but today it shot straight to half then VERY very slowly went to full. Took about 10 mins to rise slowly from half to full and never had that happen before . Wondering if it was coincidence or if the sensor was adjusting somehow . Really puzzled me and did use a few choice blue words thinking the gauge was messed up but will see with next tank.Just wondered if anyone had any thoughts or ideas ? Real puzzler!

The sensor won't be adapting, in any clever way. It doesn't.

I have seen something similar in a car which I think had a poor connection to the sensor (I never did get to the bottom of it, but I wasn't too concerned, either, as the gauge only used to take a bit of time to go up the full way, but you didn't want to get too close to empty, because you never were sure if the gauge was lying a little).

The other possibility is that the float itself is leaking and rather than just containing air it actually contains both air and fuel, and not going to right level. I'm not sure why there should be that much difference between the '99' fuel (do you get a chocolate flake in it? you should, surely?) and anything else, but it could happen.

fuel gauge just uses a track resistor, fuel grade wont have any effect on it, just a coincidence,

my opinion is 99 fuel waste of money unless you have performance car that needs it to prevet excess knock with agressive ign, fueling

your fuelling straegy on normal car takes into account the 95 as a max grade and ign and fuel 3d map is relevent to that grade.

so only marginal benefit would be the cleaning agents,not that it could be quantified as such

just my opinion, others will no doubt say otherwise.

Cheers guys , really appreciate the input.

It is a really strange one because since posting i have been googling a fair bit to see if anyone with any other car brands have encountered problems with fuel gauge and seems many have ! But even stranger is no one seems to have a reason or answer for it but most said as soon as they swapped back to a standard unleaded petrol the gauge acted normally thats why i wondered it the octane level could mess with a sensor or gauge in some way.Pleased others have had the problem as i thought there was another outlay i was going to have . Seems though the posts i saw did not say if they tried a couple of super unleadeds or just the one so may try a tank of normal and then maybe a BP Ultimate or a Shell V power and see if it happens again.

Ian with regard the reasoning you were spot on with regard the cleaning agents,it was the only real reason i did it and to see for myself if i felt any difference after reading so many posts both for and against it. Performance wise i do feel it is slightly sharper lower end but again that could be a "Placebo" effect just where i am thinking its running super so it must improve things.However i am old enough and ugly enough to know the Petrol i put in isnt going to do much really . Its a 1.8 Zetec S and no matter how much i would love to put in a tank of petrol and find it blows away ST's or RS's it just isnt going to happen.Just want to do what is best i can for the engine in terms of keeping it clean inside as long as i can.Time will tell.

My previous car needed 98+ fuel and you could tell the opposite way if I had to put 95 in , there was a 10hp or so drop , and even then it blew away St easily and rs just about. Lol.

Come on admit it,you had a 1.2 Corsa really ;-)

Not quite.

I never bother with super, it is pointless when the car isn't set to run on it. If you want cleaning agents etc pop some Shell or Esso in, they are better fuels than supermarket allegedly. I only put Esso/Shell in mine, I do like BP but not one nearby

Sent via the 'Clacks'

GNU STP

my opinion is 99 fuel waste of money unless you have performance car that needs it to prevet excess knock with agressive ign, fueling

your fuelling straegy on normal car takes into account the 95 as a max grade and ign and fuel 3d map is relevent to that grade.

so only marginal benefit would be the cleaning agents,not that it could be quantified as such

Not necessarily. If the car has knock detection (and I don't know whether your car does), then it will adapt to the use of higher octane fuel, and there will be some advantage, if only a small one.

That said, putting more octane that you need into a car without any knock detection and adaptation isn't really an advantage, just a waste of money. And don't confuse Octane with heat value; a higher Octane fuel does not imply a higher heat value, and, in fact, might be quite the opposite.

I only use Shell V Power, I've tried Tesco's petrol and the car just doesn't like it. I don't know whether it's because it's an automatic or whatever but Shell V Power is the only petrol that I'm comfortable putting in.

When my dad had the Zafira VXR (I'm sorry, I know, it was a good car honestly) that wouldn't run right without Shell.