You guys running diesel vehicles

[aboard_epsilon]

I'm not using the autostop ...you can bypass the auto stop on most pumps if you fill slowly ...and end up with fuel on your shoes

[aboard_epsilon]

North Wales, UK, imperial gallons -- 8 pints 4.54 LITRES

[A.K. Boomer]

Aboard - unless not topping off --- the autostop is highly recommended due to overfilling if not used, you can saturate emissions stuff and even hydrostatic lock your tank and cause a rupture if you put the fuel in cold and to where there's no expansion room and then drive home a short distance and the day heats up,,,

I guess i assumed you were already using it --- I would totally go that rout and recalc all your readings after a few rounds of doing that..

[A.K. Boomer]

North Wales, UK, imperial gallons -- 8 pints 4.54 LITRES

still very good mileage - good for you...

[Willy]

The brimming technique works for you, no argument from me on that level.

The very fact though that the OP brings up regarding the inconsistency of brimming in his particular case speaks volumes about this method as an unreliable method of determining an accurate mpg figure across the board. That and as mentioned, this has not been the accepted practice to those that do this on "professional' level both on air and in any publication that I have ever read. The tank only has to be filled to a consistent level. The percolation of the fuel in the fill pipe that activates the auto shutoff nozzle does this task at a very repeatable rate.
We would not even be having this discussion if your method was as consistent as you say. I suppose I'll finalize by saying...your mileage may vary.

[Mark Rand]

Diesel (at least in the UK) is more prone to foaming than petrol is. Probably just because it's got a higher molecular weight?

There is air entrainment, but it's a side effect of the auto-cutoff fuel nozzles that have become standard once ordinary punters were allowed to fill their own tanks. The original 'spout with a valve' nozzles would dispense a solid stream of liquid. All over the vehicle, pump attendant and forecourt if one lost concentration.

*Worked as a forecourt attendant for 22 hours/week from age 13 to age 18 in the '70s. Paid a lot better than pocket money, even if it was 'technically' illegal.

[A.K. Boomer]

Umm yes brimming - but whilst doing so i noticed putting it in slowly, "possibly" made the pump counter count less ...that's what the discussion is about ..
The actual fuel coming out of the nozzle frothing or with laminar flow ---- not the fuel frothing up the fuel tank filler ..and if it made a difference on the pump counter.

Aboard the answer on that one is NO - there's no difference - if there was believe me everyone would be milking a gallon and a half out of what just showed a gallon on the pump lol they are very much positive displacement meters - just like the gas meter on my house is charging me for just running my pilot lights for the cook stove... fluids are even easier to keep track of...

I read Willy's stuff and agree a double click after letting set would not be a bad thing and I have done that - I never "brim a tank" not even if expected to immediately get back into the vehicle for a long trip as you can still wreak havoc to the emission system...

[A.K. Boomer]

I will add this --- fluids aren't "dead" as far as expansion rates, they need room to grow also - heck even a typical car cooling system has to have room to grow with just 2 gallons in it, it will raise the line on the purge tank a good 2 or 3 inches sometimes --- now X that by 10 as in a 20 gallon tank of fuel, all fluids expand differently but you getta the picha,,,

"birm" a tank and then park the vehicle so that there's no room to grow and guess what? the tanks is not the only thing you may be hydrostatic locking up, with all the emissions crap routing off of tanks and running directly to the engine's intake system it's very possible the sun could come out - the day heats up and you start pumping copious amounts of raw fuel directly into the intake system and past an open intake valve and filling up a combustion chamber --- then you get in - go for a start and immediately snap a connecting rod in half... all depends on design and layout,,, these are the things a seasoned expert thinks about when bypassing what's written in every modern day cars owners manual... difference being is I know exactly as to "WHY"..

[MattiJ]

Diesel (at least in the UK) is more prone to foaming than petrol is. Probably just because it's got a higher molecular weight?

There is air entrainment, but it's a side effect of the auto-cutoff fuel nozzles that have become standard once ordinary punters were allowed to fill their own tanks. The original 'spout with a valve' nozzles would dispense a solid stream of liquid. All over the vehicle, pump attendant and forecourt if one lost concentration.

*Worked as a forecourt attendant for 22 hours/week from age 13 to age 18 in the '70s. Paid a lot better than pocket money, even if it was 'technically' illegal.

Diesel foams lot more than petrol/gasoline. Some brands are also more foaming than others.
I’m not sure if it is a molecular weight thing as kerosene/paraffin foams barely at all.

[aboard_epsilon]

OK will not brim in future ..will keep the nozzle all the way into the tank and keep clicking until it wont flow ...it will then be about 8 inches down the filler , so has room to expand ..and what with the 1/2 mile journey home should use another bit - its winter so not going to expand much
There could also be the possibility that the pump in the forecourt was faulty that day....oh yeah ..many a time I've been at a forecourt when they were delivering with a tanker ..refinery is about 30 miles away ...and the fuel was quite warm, one time i remember the stuff was very warm ...you could feel the heat radiating from the tanker when you stood within 6 feet of it.

[genea]

Don't know if i'm mistaken about this , I'm new to the diesel world - . early days

Noticed the diesel froths a lot when filling - i was brimming the tank to check mpg .

So i put it in very slowly - and noticed I put in a lot less than i usually did, strange very strange ( same pump , same side, same mileage, same runs , same driving style)

Could the stuff be cavitating in the forecourt diesel pump ...so counting froth instead of pure fuel when put in fast.

Nuts i know --- Just a thought ..how about you guys fill up very slowly and make some observations. that's very slowly so you see the fuel coming out of the nozzle without any froth in it. (laminar flow, i think its called)

all the best..mark

If the pump, fuel lines. and meter have been properly sized cavitation, before the meter, shouldn't be a problem. Air in the fuel coming out of the nozzle is introduced after the fuel has been metered.

In the US every fuel pump available to the general public for commercial use uses a calibrated, inspected, and sealed flow meter. It should be accurate to (and state inspectors certify that it is) published specs plus or minus quantization errors (errors introduced by rounding off the last digit of the readout at the beginning and at the end of each pumping session). These errors are the same whether you're topping off or relying only on the pump's meter. Topping off increases the probability of introducing additional errors.

So, why not rely on the pump reading?

[genea]

Umm yes brimming - but whilst doing so i noticed putting it in slowly, "possibly" made the pump counter count less ...that's what the discussion is about ..
. . . .

Fuel pumps use positive displacement meters. The metered fuel should be the same at a 0.1 l/minute rate for 10 mins as it is for a 1 l/min rate for 1 min. That's a characteristic of positive displacement meters, they're linear over their full design range. Turbine meters or wheeled meters are not linear except in the middle of their design range. That's why they aren't used.

[aboard_epsilon]

"so why not rely on the pump reading,"

i am ...I'm looking at the litres delivered and noting it from one fill to the next

as regards brimming ..i will not do it anymore ..i will pear down the hole and let it come up to the height of the nozzle

as regards relying on the auto shut off .......there is inconsistency with that ....they shut according to how much pressure there is back up the extra hole in the nozzle ...too much going in ..click ...too much froth coming up filler tube - click .............if you fill it too quickly - click.................. wrong angle on the nozzle - click ..............how you can say that is consistent and leads to accuracy ..i don't know

The method of brimming brought it up to the same spot within a few CC - probably plus or minus 30cc which would not even work out to be a 0.5 mpg error when you are talking a full tank.

The ambient temperature and temp of the fuel would lead to inconsistencies on how much you could get in - cant do anything about that ...but Britain is mostly the same this time of the year between 2 and 10 c degrees in the past month.

all that does not matter ...as the question was ...does frothing fuel fool the metering apparatus

[PStechPaul]

Perhaps you can check the pump meter's accuracy by filling a 5 gallon fuel container once as rapidly as possible, and another time as slowly as possible. Once that has been verified, you can use whatever method you like to determine the vehicle's fuel economy.

[genea]

...as the question was ...does frothing fuel fool the metering apparatus

Any frothing you're seeing takes place after the meter. If frothing took place before or in the meter it would show up when the pump was being calibrated.