CHRIS_D

I was travelling to a friends today and my fuel light came on, so off i set in the hunt for optimax.

Out of luck i had to use BP ultimate at 89.9p a litre

I put a tenner in which took my fuel gauge up to 1/4 tank, yet the fuel light remained on. (may i also point out i had a lot of knock link activity where as i wouldnt with Optimax)

Thing is, this isnt the first time its done it. everytime i've put ultimate in when the fuel light is on it stays on, even with a substantial amount. Yet as soon as i top it up or fill up with optimax it goes out.

Is my car trying to tell me something ??

chris




Also, whilst im on about, how do they justify selling ultimate (which is basically what used to be BP super unleaded 97 Ron) at 89.9p a litre when optimax (at 98.6 ron) is only 86.9p a litre. robbing barstewards !

chris's scooby

Esso SUL is about 80.9 round here.

Don't know about the fuel light but your not the 1st to have Knocklink activity on the BP stuff.

Chris

AndyC_772

iTrader: (2)

What's your car? What rating of fuel is it mapped for?

CHRIS_D

sti5 unmapped, so i was expecting the knock, but not as much as what i was getting

Brother_Will

Maybe its a sticking fuel guage since you probably only refill with ultimate when the tank is nearly empty and its an emergency, maybe it only sticks at the bottom but putting more in bumps it off where its sticking

CHRIS_D

no, i've filled with optimax when the light is on too - plenty of times with no problems. it's only when i've been caught out that i've had to use BP and when this happens.

its not a sticky fuel gauge as the fuel gauge moves / has moved.

if i put a fiver of optimax in tomorrow, i would bet the fuel light would go out.

chris's scooby

When my light comes on i still have about 8 or 9 litres left in the tank. If you let it get to running on vapours then maybe £10 at that price would only get you to the point when the light first comes on.

Chris

CHRIS_D

yeh i know what you mean

i got to the bp garage within 5 miles and i definetely have 1/4 tank after putting a tenner in. fuel light usually doesnt come on until just above the lowest mark.

i'm sure its the BP ultimate

si97

you need to fill above 15lt for the light to go out. its in the handbook.

MarvSTi5

Mine does the same thing Chris - found out the same way too!!

CHRIS_D

i definetly have more than 15 ltr in it.

at last, marv. someone who knows what im on about. either that or its an STi5 thing.

dij

so have you put a £10 of optimax to see if you still get the same thing?

It sounds like one of the floats in the tank could be faulty/stuck.

The right side of the tank fills up first,then it flows over to the left.
The fuel pump sucks fuel from the left to the right side of the tank (the same side that the pump is fitted to) and the two senders(floats) divide the two readings to give your fuel gauge its position.

or maybe your car has a special feature that tries to stop you from getting ripped off.

I paid 92.9p from BP recently.........big barstewards

wide

what a crock of dung how does the fuel light know what fuel is being put in

CHRIS_D

i definetley thinks its the latter mate ;0

im off now for 2 weeks so wont find out until i get back

AndyC_772

iTrader: (2)

If the gauge itself works then the float is fine.

More than likely it's just that the light goes on at one level, but doesn't go off again until it reaches some much higher level. This is called 'hysteresis' and is an extremely common technique used in electronics to filter noise from an on-off type of signal. In this case, the 'noise' is the apparent fuel level varying as it sloshes around the tank.

dij: are you sure about that? It sounds from your description as though the fuel pump could find itself sucking on air while there's still fuel in the right side of the tank. What stops that happening and ensures that all the fuel in both havles of the tank is available?

pflowers

Hi, this problem is not unique to the Scoob. I used to have a Cooper S and after filling with certain fuels the guage would give an incorrect reading ie. Tank brimmed and reads 3/4 full. This problem was noted by many other owners, MINI changed tanks, sender units etc but the problem never went. They put it down to the fuel.

I would agree about the light going on / off at different levels, mine comes on when there is about 8 litres left, but even if I put some in immediately after it takes at least 7-8 litres to go out again.

IMO there obviously is something about certain fuel that makes the float not 'float' quite as high in it, sounds bizzare I know but it would explain this problem and others.

AndyC_772

iTrader: (2)

"Density"

Surprised there's much variation between fuels, though.

krazy

I'd be surprised if there's that much difference too, but optimax is considered to be quite high density in comparison to other petrol, part of the way they can improve fuel economy. Also some bikes (usually tuned/track examples) often require rejetting 2 cope with the increased density of optimax cos they run lean at high rpm's.