Fuel Gauge not going down

[MikeSh]

1 hour ago, Roy124 said:

extra fuel will end up running into the small drain under the entry and onto the ground beneath your vehicle

I think that's very out of date. For a long time fuel systems have been sealed for emissions regulation - if you can see a small 'drain' there it's probably the return from the injection system.

There is sometimes a drain in the well outside the filler, but you'd be a bit daft to fill it that far 🙂

[Roy124]

2 minutes ago, MikeSh said:

I think that's very out of date.

I don't know enough to agree or disagree, all I note is this advice was restated only last year.

I did ask, how much fuel do you get it after the click?

[Trewithy]

The fuel tank is part of the fuel and emission control system and is a sealed system.  That's why you sometimes hear a hissing sound when you undo the filler cap.  The emission system connected to the filler pipe is there to collect petrol fumes.  When filling with petrol you should not fill beyond the first click off  as you risk getting liquid petrol into the emission control system which it is not designed to handle and could lead to an expensive repair at the next MOT.

[anchorman]

9 hours ago, Roy124 said:

I think the Car Care Nut had something on this.

How much more fuel do you up in after the first click?

Fixed or not, I don't know.

He does but he’s wrong.  I like his programs but he comes out with some tosh at times.  It might have been right many years ago with early charcoal filters but these days, the risk comes from expanding fuel on a hot day.  

[dannyboy413]

14 minutes ago, anchorman said:

the risk comes from expanding fuel on a hot day.  

When I fill up, I usually 'round up' to the next Euro. 9 times out of 10, I use the same petrol station and then drive 20 miles home, so use between a third and a quarter of a gallon, (I love the mpg figures of my car 😊). Out of interest, how much does 40 litres of petrol on a hot day expand ?

[Cyker]

It depends on the car and region - A lot of USA cars have charcoal canister EVAP systems which *will* be damaged by over-filling fuel; I think it's a lot rarer in the UK and Euro-zone cars though.

As for the fuel level, there are so many ways it could be made more accurate. The easiest would just be a lookup table or compensation curve coded into the readout - Trivial to program in once you'd measured things to know how much to compensate. Another way would be to change the resistance strip in the sender - The float is very simple; It's just an arm that moves a contact on a resistance strip; I suspect the default one is linear, so they'd just need to put in a more logrithmical (Is that even a word?? )-type one

[MikeSh]

1 hour ago, dannyboy413 said:

Out of interest, how much does 40 litres of petrol on a hot day expand ?

Assuming it comes out of the pump at 15°C and while in the car gets to 25°C then about 1/3 litre.

In an extreme case of say 10 - 30 about 3/4 litre, but that's very unlikely. (Fuel comes out the refinery fairly warm, so I'd be amazed if the underground tanks at the filling station got below 15 even in winter. And even on a 30°C day a full tank isn't going to heat up to ambient before the sun goes down.)

[Mooly]

12 hours ago, Cyker said:

As for the fuel level, there are so many ways it could be made more accurate. The easiest would just be a lookup table or compensation curve coded into the readout - Trivial to program in once you'd measured things to know how much to compensate.

Exactly, it is easily do-able and at zero cost, it is just a change as you say in the look up table.

 

11 hours ago, MikeSh said:

Assuming it comes out of the pump at 15°C and while in the car gets to 25°C then about 1/3 litre.

It been said for a long time that the best time to get fuel is in the early morning because of this. Probably fairly small in the scheme of things but better to have it than not.  

[Roy124]

@MikeSh all of 4 miles extra.  Hardly worth the effort to hold the trigger. 😂

[Guest]

I can only echo what othes have written about the fuel gauge. My car has a "conventional" gauge and when the tank is filled to the first click (yes, I still don't want to risk overdoing it) I have to drive about 40 miles before there is any movement of the needle from full. Then it drops like a damn stone! I have found it to be accurate though once it does move downwards. At half a tank, on the gauge, there's room for about 20 litre in the tank (42 litre capacity?).

When possible I fill up at just under half, allegedly the fuel remaining helps to keep the pump cool?

[Mooly]

7 minutes ago, Slartybartfast said:

When possible I fill up at just under half, allegedly the fuel remaining helps to keep the pump cool?

It does I believe. A couple of years ago I covered around 30 miles in our Corolla 1.4 with the low fuel light on. I knew there would be enough in to get home but I noticed a strange low frequency 'hum' whenever I pulled up at lights near the end of the journey. It was constant and unchanging with revs. It was also a very hot day. 

Got home and then went to fill up. Noise still there. I think its a 55L tank and I got something like 51 or 52L in. Noise gone. I did a quick search on-line about the noise as I guessed what was happening and the lack of fuel was not dampening the sound of the pump. Lots of hits for 'Toyota' and 'Low Fuel' and 'Pump Humming'.

[MikeSh]

2 hours ago, Mooly said:

It been said for a long time that the best time to get fuel is in the early morning because of this. Probably fairly small in the scheme of things but better to have it than not.  

They said for a long time the sun went round the earth. The fuel in the station thanks won't change temp, so it won't be cooler in the morning.

You also won't get 'more' as it warms up in your tank because the energy is in the mass not the volume.

1 hour ago, Roy124 said:

@MikeSh all of 4 miles extra.  Hardly worth the effort to hold the trigger. 😂

I wasn't saying that's the volume you get by filling longer, just how much what's in there might expand. If there isn't enough space for that expansion then something has to give, but I suspect the manufacturers have thought about that.

[TonyHSD]

Lol I missed on this one. 
All these petrol overfilled tanks are simply a myths , at least on our cars made  MY 2000-> .
In London there are some garages located on hills, such a big  one that when you fill up you can get your petrol tank and filler neck full , plus some fuel getting out of the car on the floor, but then when drive off you have one bar less , because you actually had not filled up full but because the car was parked on incline the petrol got out and even the pump didn’t clicked and stopped. I don’t know why it is allowed to have petrol stations build on not level ground?! 
Happens few times to me at the same place. Shell on A406 near Neasden north west London.
I had been doing rounds after first click for many years, three full fill ups per week and never had any problems on any car.  
The first bar down usually happens at aroma 60 miles in my Auris hybrid, and I usually refill when below half or 1/3 petrol remained, once driven below 0 miles around 20-30 miles in negative, but that is not important. More important is that my car is 13.5 years old with 278000 miles and never had anything replaced on the fuel system except a recall on the filler tube done by Toyota back in 2016. So far everything is original and still works as day one. 
 

[ColinB]

Being an old biker I always set the trip to zero when filling up (bikes generally don't have fuel gauge and, if they do, they are totally inaccurate). Not really a problem with my RAV4 as it has a range of ~500 miles, but I will have to be more careful when I get my Yaris Cross with its much smaller tank. 

[Rhymes with Paris]

1 hour ago, ColinB said:

Being an old biker I always set the trip to zero when filling up (bikes generally don't have fuel gauge and, if they do, they are totally inaccurate). Not really a problem with my RAV4 as it has a range of ~500 miles, but I will have to be more careful when I get my Yaris Cross with its much smaller tank. 

I had a bike with a fuel gauge on it Colin, but pretty useless as it guzzled fuel and had a small tank underseat instead of on top of the frame.

Damn thing wouldn't do more than 50 miles or so without the fuel warning light coming on.

It also had a handy design feature that resulted in the key and fob that I had to use to open the seat to get to the filler, dropping into the gap in the super heated exhaust pipes.

Which was handy, considering I had to fill it up several times on a ride.

 

[Cyker]

Ack that sounds painful; A bit like the bonnet strut on my Mk4, which lives riiight over the engine, which it turns out gets quite hot during use!  

 

Actually do petrol engines have return lines to the tank? I know diesels generally do, which is how they try and stop it gelling up in winter, as hot diesel returning from the engine helps warm it back up...!

[Rhymes with Paris]

30 minutes ago, Cyker said:

which is how they try and stop it gelling up in winter, as hot diesel returning from the engine helps warm it back up...!

Can you remember the lines of stopped wagons on the A1 with small fires 🔥 under the fuel tank to de-wax the diesel during the really bad winters 🥶.

I think this was before modern additives to prevent this were widely available.

Not really recommended on a small Citroen diesel though, as apparently setting fire to your own car was not covered by insurance.

 

[Juedan2011]

An update 😁 

It's finally dropped one blue bar today after about 120 miles 👍

So now I should see a regular drop now it's started to drop? 

[Cyker]

Not only regular but probably rapid  

[yossarian247]

49 minutes ago, Rhymes with Paris said:

Can you remember the lines of stopped wagons on the A1 with small fires 🔥 under the fuel tank to de-wax the diesel during the really bad winters 🥶.

I think this was before modern additives to prevent this were widely available.

Not really recommended on a small Citroen diesel though, as apparently setting fire to your own car was not covered by insurance.

 

The owners manual of my 1980s Citroen diesel actually recommended adding a gallon of 2 Star petrol to the diesel tank in winter to improve cold starting and help to prevent fuel waxing!

[anchorman]

1 hour ago, Rhymes with Paris said:

Can you remember the lines of stopped wagons on the A1 with small fires 🔥 under the fuel tank to de-wax the diesel during the really bad winters 🥶.

I think this was before modern additives to prevent this were widely available.

Not really recommended on a small Citroen diesel though, as apparently setting fire to your own car was not covered by insurance.

 

I was lay under the things with ice cold diesel running down my arm.  

[Cyker]

Yikes, that doesn't sound fun at all... no wonder you're so grumpy!   

 

 

[Primus1]

I never go to the first click, when filling up, I just wait till the wife shouts “ how f#### much” then I stop..

[MikeSh]

21 minutes ago, Primus1 said:

I never go to the first click, when filling up, I just wait till the wife shouts “ how f#### much” then I stop..

Yeah, you spend your life as their personal 'free' taxi driver and they still moan about the cost.

[anchorman]

9 hours ago, Cyker said:

Yikes, that doesn't sound fun at all... no wonder you're so grumpy!   

 

 

Compounded by age and made exponentially worse by modern wokeness.  I’ve started growling like Clint Eastwood in Gran Torino.