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My cars manual states that the fuel tank holds 17.4 US gallons. I am not one to be silly enough to let my car run out of gas but recently I had let it get down to the very bottom and upon fueling up was surprised when it took 18.66 US gallons. This is how much was filled with the pump automatically shutting off(no topping off). I was very surprised as none of my other Saabs ever did this. My curiousity made me try it again and once again I was able to fill it up 18.64 US gallons(no topping off). What I am getting at is if the computer uses overall capacity in its equation could this discrepancy be the reason for all the eratic MPG readings? Sorry for the long story. I am going to post this on a fresh thread for extra feedback.
 

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Alix,

Were the two fill-ups performed from different pumps/garages? If not, maybe you were just given short measures? It happens in the UK all over the place.

Try filling up a few more times using different garages & compare deliveries.
 

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Don't forget you have the fuel tank then the fuel rail, pump and pipes leading to the filler neck. This can easily add a litre or 2 to the specified capacity. I have filled up with >65 litres once before.
 

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Yes John. It is illegal. Doesn't mean it doesn't happen though does it.

Murder
Rape
GBH
Burglary

Just a few other things that are illegal yet THEY happen...

At the end of the day & filling station will make just a few pence profit on a litre of fuel. Not surprising then that some of the less scrupulous sorts out there will fix their pumps to deliver less than what's registered as being delivered. Not by much but on a tankfull you might expects to be dished one or two litres less then you think you've got.

I certainly wouldn't be surprised anyway. I think it's definitely worth trying different pumps & garages.
 

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Hey Guys/.
94 2.3t etc..
My tank takes around 15.5 gallons. If I thought it took an extra litre or two, I wouldn't put a brick in the tank to compensate. I fill up, run out, fill up again.
Obviously if my average MPG is down, I would do something about it, but size of tank wouldn't alter anything. Sorry if I am missing the point of the thread, or did I just have a bad day at the office ??
Andy
 

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I think it is Customs and Exise (Weights and Measures), who you could speak to. At least then if a Garage is shortchanging us, somebody could have a good day - the smile wouldnt be on the garagemens faces - and we could gradually be assured that we were getting what we pay for, expensive enough as it is!
 

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Some time ago , I was enlightened by a fuel pump fitter,that there is a tolerance in the pump and it can be set to deliver either end of that tolerance.So yes there may well be a differance at differant forecourts,but how much I don't know.
 

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Yes, I know illegal things happen. The key part of my post was Is there any basis for this?

There is no point making allegations unless there is evidence to support them. I have not seen any evidence that suggests this practice is widespread.

I am open-minded on these things and my question was a genuine one. Let's remove the emotion and introduce some rationality into the discussion, please.

Cheers
/john
 

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Petroleum expands by approx 0.11% per celsius degree temprature rise, so as it rises a smaller quantity mass is delivered, so for a larger "mass" buy your gas only from cold petrol stations.lol guess us saab owners are screwed with all this global warming...at least the air cons still working, but it is still winter...Alix66 it must of been boiling when you filled up
 

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mpen- well you learn something new every day - I did not know this ;-)

By my calculations, filling the tank with 65 litres at £0.69 per litre would cost £44.85. A one degree increase in fuel temperature would suggest that you only got 64.92857 litres costing £44.80.

Are you saying that 64.92857 of expanded fuel can register as 65 litres? In which case there is a £0.05 difference.

(I am not saying that my method is correct, mind)

What is the starting temperature - the temperature at which the litre measurement is accurate?

I can't help thinking that this is a bit silly. After all, your driving style is likely to have more of an impact on your fuel costs and I do not think you can really hold garages responsible for marginally short measure (if indeed this is the case) that is down to fuel expansion cuased by temperatures.

You can not hold the garage responsible for the weather - that is more likely down to your fossil-fuel burning antics in your aeros and carlssons. Is it not? ;-)

/john
 

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John, I am no expert on this, my father used to be in the petrol industry, he always told me to fill my car early in the morning..I always thought he was winding me up..so I had him a bet one day.........and lost...it seems this is quite an issue in auzzy..If you search on google/yahoo it pulls a lot of info up
Mark
 

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personally I don't care if my car holds more than .5 of a gallon more one week than the other..I don't care if it only shows 21.2mpg which it always seems to settle on..I didn't care that it cost over £4.500 in repairs and messing about last year(my wife did)I just like driving it
 

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Allow me to start by apologising for any aggresive undertones in this post. It's late, I'm tired but it has to be said!

<Snip>
Yes, I know illegal things happen. The key part of my post was Is there any basis for this?
<End>

Only Alix66 might be able to answer that one John. I brought the subject into the thread so that people become aware of it as a possibile cause for variances in fuel take up.

Isn't that the point of posting? To bring people into your line of thought(s)?

<Snip>
Let's remove the emotion and introduce some rationality into the discussion, please.
<End>

As above John. I brought this up so as to allow others the benefit of this being a possibility. I fail to see where any emotion lies other than within your post. Alix66 asked a perfectly reasonable question. Why shouldn't he know about this additional fuel capacity? The purpose of this site is to share knowledge & "help" each other out by offering suggestions & tips. If you're not interested then just press the back button & move to a thread that is of interest to you. I have better things to do than read patronising posts. We all have that choice both here & on any other board. Ironic then that your very next post on this thread contradicts your own expectations of what should be posted on this site!

You had a bad day John?

<Snip>
Alix66 it must of been boiling when you filled up
<End>

This is irrelevant! The pump will deliver (within the tollerances that mikeh mentions in his post) the correct amount of fuel regardless of the temperature. Sure... As the ambient temperature fluctuates so will the volume of fuel fluctuate I accept that. What I do not accept is that the amount of fuel a pump delivers fluctuates depending on the temperature. One US gallon is one US gallon but only when delivered. What happens to the volume of the fuel after that is another matter. We've all had fuel spew out when releasing the pressure in a jerry can. What Alix66 is saying is that he was able to get more fuel in than his car is supposed to be able to take on at the point of delivery. Think about it.

Finally (And as I said I'm not being aggresive ok?) both mpen & Andy bowles I don't think that your comments are at all constructive in light that a fellow member has put a thread on this board asking for your thoughts & you then "don't care" about things like your running costs. Neither do I to be honest. Surely if the content of a post or a thread is deemed to be unsuitable then the list administrators will soon make their thoughts known.

I find certain members comments in this thread to be contradictory, unhelpful, patronising & condescending. I resent being spoken to like this & we all deserve to give each other the respect that adults are supposed to give each other. We are all adults I presume. We all can & do provide constructive informative posts. So why the change here then is beyond me. If you don't have something constructive to say then why say anything!

I will not be replying to any further whispers on this thread on this issue as that is unconstructive & likely to ensure a swift response from the administrators. I hope that they do not feel that this post should be removed as I think it's important that we show each other the respect that we all deserve.

I've made my point so please take this on board & now please... Lets get on with it!
 

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Mark hits the nail on the thumb! ;-)

My question was one of genuine interest - I had not heard of this fuel expansion before. I am openminded and I learn new things every day.

I have noticed that some people on this board are quick to criticise and quick to make allegations. If there is an allegation about short measures of fuel, I was just asking the basis of that allegation.

I think some people need to relax a little. I thought Saab drivers were friendly? I've had a very good day, that's why friendly discussion is not a problem for me.

/john
 

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If fuel consumption were truly of importance to a driver/owner, the SAAB would not be the car of choice, not so? There is a cost in hurtling 1.5 tonne around our roads. To my mind the most useful part of this thread is some yardstick by which we compare consumptions, re-evaluate our driving (and pleasure), and perhaps pinpoint a correctable mechanical fault.

I am a great enthusiast for polite, helpful, and friendly support from like-minded individuals. These characteristics appear to predominate, thank goodness.
 

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As a Saab driver, I have always been interested in a reasonable on fuel consumption, and I think an average of between 28 to 34mpg suits me fine.

In response to Alix's original query:

I can only imagine that the difference in manual spec (17.4 US Gallons) and actual tank fill up capacity (18.66 USG) is due to the additional capacity of the filler pipe - but this doesn't explain why your earlier Saabs did not have the same 'fill up' capacity - unless they were different by design, with shorter pipe to tank.

The larger tank could 'not' be the cause of 'erratic MPG readings'. Any discrepancy in tank size would result in 'consistant' MPG readings (i.e. consistent margins of error) on the fuel computer readout.

Very interesting info on fuel expansion. I am inclined to agree with 900016Turbo's comments on volumn of fuel delivered by the pump. Actually, the expansion of the fuel tank is more likely to have an effect on the volumn it can hold. In hotter weather the tank will hold more than in cold weather. But very little expands/contracts significantly within a tempreture range of -10C to 30C (40 degrees C). So this cannot be the problem - in my humble view!
 

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With regards to fuel pump tolerances:

The law in the UK used to allow a 10% margin of error which stemmed from the early days of motoring when 10% was as accurate as they could manufacture pumps. With the improvement of technology the pumps got more accurate but the law stayed the same. So it got to the stage where the pumps were set to underfill by 9% and still remain legal. Weights and Measures did ask for the law to change but I don't know if it ever happened.
 
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