I got down close to empty a couple of weeks ago and the alarm in the car went off. Drove about 25 km to the first caltex station and put in 50.1 litres according to the pump.
Same thing happened today, but I was a bit closer to the local Caltex/Woolies station so I went there to collect the $0.04/l discount. Still about 25 km, but this time it sold me 52.5 litres for the fill.
That's a 5% difference and at least one of them is wrong.
Anybody know how often pumps are supposed to be calibrated?
I'm not sure if petrol pumps are checked by the govt. any more [well...here in W.A. at least]
The difference between your two refills is more likely to be due to your vehicle itself.
Parked on a slight slope, on uneven ground, how your car is loaded [dragging it's bum]
Any or all of these can result in different fuel capacities due to the shape of the fuel tank and it's pipework.
However, recently - my local servo had a dodgy valve[or something like that] in one of their pumps which allowed fuel to drain back.
If the pump was unused for a while, it racked up about 40 - 50 cents before any fuel came out the nozzle, it was pretty obvious as you could hear the pump racing and surging.
I told the operators and they isolated & tagged the pump, drove past a few hours later and a service van was onsite with the pump in bits.
p.s. avoid overfilling your tank by "overclicking" the fuel nozzle, it floods the emission control charcoal canister and over time can stuff it up badly, letting bits of charcoal migrate into fuel lines, and the tank itself.
5% difference between 50 and 52.5 litres. The car was on level ground both times with the same load.
I did a quick search and found that pumps are allowed a 0.3% variation when they are made, but don't seem to be tested later.
State and Federal based weights and measures dept are supposed to check the calibration. They check the retail scales, packaging etc.
I think complaints to federal measurements will be investigated by state Fair trade.
www.industry.gov.au/strategies-for-the-future/national-measurement-institute't-get-caught-out-with-underweight-products!.aspx
They are supposed to do random checks but who knows how the funding is this term.
Anecdotally they came out to an extremely remote area I was in with a large tapered jug to check the fuel pump and set of weights to check the scales at a community store completely unannounced. They passed.
Could be as simple as your tank float / sensor going off earlier the first time, as you drove on a hill. eg my car beeps like mad and says 5km to go when its in the driveway, then down on the street it immediately says 80km to empty.
So in the first occasion you drove up or down hill which set the sensor off 2.5l "early"
But yeah, the lack of fuel bowser calibration in WA now is crap. A family member had a pump that was obviously wrong and brought it to the attention of the petrol station who knocked some money off the bill. Out of curiosity he rang the weights and measures mob at Consumer Affairs who said it is no longer done "because the public didn't really want it". Bovine faeces, I am sure we all want to get a correct measure 
Consumer affairs might be right about lack of interest. I Googled "petrol pump calibration" and got this thread on the first page of results.
I still think that the local Woolies/Caltex is suss, just because a few months ago it sold me very close to the theoretical tank size before the low fuel alarm sounded
I own a servo, We calibrate/check our pumps once a year. No authority has ever checked ours. If you fail to have the calibration checked by an accredited technician for more than two years and are audited, the pump will be shut down until checked and signed off by a technician.
We choose to test them annually.
The test measure is 15lt and I think 30ml is the tolerance either way( if I remember correctly)
The 15 lt test can is filled 3 times, fast, slow and stop start, this is particularly important for diesel because it foams and you have to make sure the systems on the pump are functioning correctly so customers are not paying for air.
When we bought the servo, the pumps hadn't been checked for years, they were still all within tolerance,, in favor of the customer.
My local servo has one pump that I never use because it consistently put a lot more fuel into my car than the size of the fuel tank. 
I have seen people stop the pump by pushing in the lever where the nozzle sits and then pull the trigger and draining the fuel that is still in the hose into their tank.
Im guessing there may be a litre or so free.
the next person gets duded as the hose has to re fill when pumping starts.
I don't now how common this is or if it actually works.
Select to expand quoteJolene said..
I own a servo, We calibrate/check our pumps once a year. No authority has ever checked ours. If you fail to have the calibration checked by an accredited technician for more than two years and are audited, the pump will be shut down until checked and signed off by a technician.
We choose to test them annually.
The test measure is 15lt and I think 30ml is the tolerance either way( if I remember correctly)
The 15 lt test can is filled 3 times, fast, slow and stop start, this is particularly important for diesel because it foams and you have to make sure the systems on the pump are functioning correctly so customers are not paying for air.
When we bought the servo, the pumps hadn't been checked for years, they were still all within tolerance,, in favor of the customer.
Interesting, cos weights n measures said they don't
How often do they do a random check?
Select to expand quoteHarrow said..
My local servo has one pump that I never use because it consistently put a lot more fuel into my car than the size of the fuel tank.
Yep, I've seen that happen where I am too. Dodgy as.
Select to expand quoteMark _australia said..Jolene said..
I own a servo, We calibrate/check our pumps once a year. No authority has ever checked ours. If you fail to have the calibration checked by an accredited technician for more than two years and are audited, the pump will be shut down until checked and signed off by a technician.
We choose to test them annually.
The test measure is 15lt and I think 30ml is the tolerance either way( if I remember correctly)
The 15 lt test can is filled 3 times, fast, slow and stop start, this is particularly important for diesel because it foams and you have to make sure the systems on the pump are functioning correctly so customers are not paying for air.
When we bought the servo, the pumps hadn't been checked for years, they were still all within tolerance,, in favor of the customer.
Interesting, cos weights n measures said they don't
How often do they do a random check?
I don't know Mark, as I said we have never been checked, maybe an audit isn't random but a follow up from consumer complaints or information provided from another dept such as dangerous goods (job details from fuel techs)
We have been audited by Dangerous Goods a couple of years back but to my knowledge they didn't inspect the pumps for the silver stickers that the fuel tech guys leave on them. There's lots of rumors around, things like dangerous goods licences not been renewed untill tank leakage and ground contamination levels pass tests, something that at one time had nothing to do with DG as it was an EPA issue but it all seems to be part of the pie now. Maybe fuel watch has inspectors, they seem to prosecute retailers for advertising a different price to what is at the bowser.
We also have post office weight scales in the store, same deal, we have them checked and adjusted by a tech,,, and he puts the little sticker on them,
Weights and Measures are suppose to check those too but we have never seen them.
Select to expand quoteCraig66 said..
I have seen people stop the pump by pushing in the lever where the nozzle sits and then pull the trigger and draining the fuel that is still in the hose into their tank.
Im guessing there may be a litre or so free.
the next person gets duded as the hose has to re fill when pumping starts.
I don't now how common this is or if it actually works.
Automatic fuel delivery nozzles require pressure from the pump to open the delivery valve,, so its basically impossible to drain the hose unless the valve is faulty. People that do it don't realize this.
The Anti drain allowance for the bowser to pass calibration is MinMeasureQuantity x 0.3% . So if MMQ is about 20 Litres then max allowable is only 60 mls.
So as per above. Two parts of stuff all.
If you are really worried , take a 20 ltr fuel container and fill that first, you can then see if it is accurate or not.
Because you can be really really sure that the 20l fuel container holds exactly 20l .............. NOT, it's a bit like the size of your fuel tank in the car, what it says on the spec is a rough guide if your trying to call someone out for cheating you.
I have heard of one case of a servo fiddling with the pumps and that was 25 years ago, he soon went broke and was hounded out of town when found out. I really doubt that the big guys would even dare take the risk, and like all conspiracy theories....... how are they gonna make everyone keep the secret?
Select to expand quoteJolene said..
I own a servo, We calibrate/check our pumps once a year. No authority has ever checked ours. If you fail to have the calibration checked by an accredited technician for more than two years and are audited, the pump will be shut down until checked and signed off by a technician.
We choose to test them annually.
The test measure is 15lt and I think 30ml is the tolerance either way( if I remember correctly)
The 15 lt test can is filled 3 times, fast, slow and stop start, this is particularly important for diesel because it foams and you have to make sure the systems on the pump are functioning correctly so customers are not paying for air.
When we bought the servo, the pumps hadn't been checked for years, they were still all within tolerance,, in favor of the customer.
I calibrate fuel pumps for many customers over the years. Since going federal with National Measurement Institute, there is no set guidelines on frequency of testing as the onus is left with the owner to get them tested. Like most sites as Jolene said they would call someone like myself to get there pumps tested and reverified. Everytime we carry out a test paperwork is sent to NMI to let them know that a pump has been tested and passed. Most cases with fluctuations in litre amounts is the tank itself when temperatures change.
You will probably find it's your car calculating your distance left on remaining fuel taking into account current instant fuel use. For example, the car will beep saying only 80km left much later if you have recently been doing long distances.
...or manufacturers overstating the size of the tanks.
My Troopy has 2 "90L" tanks... only ever got 85L into either of them - that's running them totally empty and fuel spilling out the overflow.
Rod - the fuel tank vent pipes may be sitting too low in the tanks.
I know of a couple of diesel GQ/GU patrols that gained a bit extra tank capacity by opening the tanks, bending the vent pipes upward so they are closer to the ceiling of the tank.
Between the 2 x tanks the fellas reckon they get about 15 to 17 litres extra.
Downside is they can only fill all the way immediately before a long drive, as the 2 x tanks are verging on overflowing, so not much good in city stop-start traffic with lots of cornering.
