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Peter Fenwick View Drop Down
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Direct Link To This Post Topic: More fun with petrol!
    Posted: 05-April-2004 at 12:26

last week I had to fill up with super UL from Total as I couldn't find a shell garage anywhere. Any how just filled up again this morning and worked out that I managed a staggering 24.6mpg. The computer claimed 30.4 and although this is always a bit more optomistic than actual it is not normally 6 mpg out. I haven't even been thrashing it over the last week or so. Can the difference in petrol quality be that much?. I have just had four new tyres put on but again I can't see how that would make such a big difference to my fuel consumption. To put it into perspective this is the worst I have ever had, including weeks where I have really thrashed the car and when we had all the snow and the car was stationary with the engine running more often than not. Any one else experienced anything like this before?

Entering an age of Austerity and now driving a Focus Diesel.
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Alex View Drop Down
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Direct Link To This Post Posted: 05-April-2004 at 12:37
Seriously doubt the difference is down to the petrol. The tyres are much more likely to cause a difference, particularly if they are too soft. Town driving or short journeys would make an even bigger difference, even if the car was driven gently. Even so, there are far too many variables to make a judgement so quickly. You'd need to run it for some time (like 10 fill-ups) and take an average reading to compare the fuels.
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Peter Fenwick View Drop Down
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Direct Link To This Post Posted: 05-April-2004 at 16:14

Alex,

I don't think it is down to the petrol to be honest. I would also be very supprised if tyres can make such a difference.

I have done nothing out of the ordinary this last week in fact it has been fairly typical of most weeks driving. The only two factors which have changed are tyres and petrol. In all the cars I have owned I have never seen such big variation in mpg and I have never noticed tyres or petrol make a difference. In fact the only time I saw the mpg drop off was when the car had a problem which is why I am a little concerned.

Entering an age of Austerity and now driving a Focus Diesel.
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Alex View Drop Down
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Direct Link To This Post Posted: 05-April-2004 at 16:49

Fair enough. The tyres would only make a large difference if they were particularly under-inflated.

I wouldn't panic about the car though. Give it another tank or two - maybe the last fill up was just a random blip.

Also, another thing that can affect it is the amount of fuel the pump puts in before it clicks of, which varies from pump to pump. Perhaps the Total pump put less fuel in.

Alex Shirley


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Direct Link To This Post Posted: 07-April-2004 at 11:28
Odd one that, as Alex says i'd suspect the tyre pressures first, we should all know by know that "specialist" tyre fitters etc. seem to have the most erratic guages imagineable when it comes to your tyres. I always check afterwards on my own digital guage and it's surprising how far out they can be - I started checking like this out of habit of doing so on the 'bike.
When I had my 18's fitted I asked for 35psi all round until I could get a proper figure to use, when I checked them next morning they had 29psi in!!

1990 525i SE M-Tech (for sale)
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Peter Fenwick View Drop Down
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Direct Link To This Post Posted: 07-April-2004 at 12:19
I checked the pressures as soon as I left. I currently have 34 psi in the front and 36 psi in the rear. I supect that it is down to a dodgy petrol pump claiming that it has put more petrol in than it actually has. I wonder how often these things are calibrated? I bet it isn't very often. I was speaking to a rep yesterday who does 30K miles a year and he says that on occasions he has had pumps claim to have put more petrol in than the capacity of the fuel tank.
Entering an age of Austerity and now driving a Focus Diesel.
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Direct Link To This Post Posted: 08-April-2004 at 19:06

I have heard from other sources that in some cars the more expensive petrol, does in fact improve your fuel economy.

I cant remember the reason why, but I believe it was something about the octane levels and that it can use the fuel more efficiently as it has better properties

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Direct Link To This Post Posted: 09-April-2004 at 08:08
Well the shell optimax I was using before that was giving me 28mpg has an octane rating of 98. The total Super UL has an octane rating of 97. However the morrisons premium UL that I used when I first got the car is only 95 and I got better mpg than with the total. Go figure?
Entering an age of Austerity and now driving a Focus Diesel.
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