how does my petrol tank/gauge work?

[Tidy Max]

This is something i have thought about but never found out the answer, in my head a petrol tank looks like a toilet cystern with the floating ball which would be an indicator to your petrol gauge on how much fuel you have left?

since installing my gsi clocks my gauge goes all the way to the bottom of the red, then when the light comes on that basically means get to a petrol station asap because your on fumes. is this right? i thought the light might indicate your into a reserve etc

thanks!

[Spudly]

Basically it works how it looks, the float stays on top of the fuel and indicates how much fuel is in the tank, the light is supposed to be a warning when youve only got a few miles left but vaux guages (especially older ones) are notorious liars so often wait till youre about to run out before warning you lol
Hth:thumb:

[Dod]

Yeah, to keep it simple, you got it in one!!

There isnt a float in all motors though, but its the same principal is the same but with a depth indicator. They need to be slowish to give an accurate measurment as cornering can cause all the fuel to rush to or away from the sender. Same reason you need a Swirl Pot in your tank as well.

[Tidy Max]

cool, i used my powers of deduction as taught by a one mr sherlock holmes lol

right so ill just keep ontop of my fuel then, the gauge is very unreliable, i dont understand why the less fuel i have, the quicker it sups it, maybe thats because of the swirl pot, i just dont know!!

thanks for your help though, another thing i can tick off the list :) cheers

[Spudly]

Because the bottom half of the tank is smaller than the top half, so when your guage reads half, due to the shape of the tank there isnt actually half left hence why it seems to drink it all faster and also why the guages are unreliable as feck lol

[Dod]

Glad to be a help.

[Welsh Dan]

Also if you get to the bottom of the tank you'll suck up all of the crap and cause problems with the pump/filter/carb.

[Tidy Max]

lol

[Tidy Max]

yeahh i know, bit late now, conked out on my drive the other night :(

[meritlover]

the float acts on a potentiometer. the gauge is really just an ammeter.

the dampening effect is achieved by the slow action of the bi-metallic strip in the gauge, hence why it apprears to fill the tank on hills, before returning to normal after a few mins of stable driving, and why the gauge doesnt bounce violently as the fuel sloshes about.

[Shaun_O'Donnell]

Also if you get to the bottom of the tank you'll suck up all of the crap and cause problems with the pump/filter/carb.

I've always had a slight doubt about this. No matter how much fuel is in the tank, you can technically still suck up crap from the bottom, it's not as if the pick up pipe rises and falls with the level of fuel. The fuel pick up is at the lowest part of the tank, is this not where the crap would settle, therefore still able to be sucked up regardless of fuel level???:confused: :confused:

[Dod]

Something I've often wondered about. Realisticially what dirt can you pick up, it has to be extremely minimal and microscopic, anyway, anything big enough to do damage surely would be picked up by one of the filters?

[meritlover]

agreed.

this man is the correctest.

pump fuel is clean anyway, and the filter is there to stop the crap getting into the carb/injectors.

if youve ever cut open a tank. (even a very rusty one) it is often nice inside.

[Dod]

Thank you.

[Shaun_O'Donnell]

I'm sure the pick up pipes also have a gauze filter on the end.

[meritlover]

it does, but it should really be a minimum of 40microns to be any use. thats mostly to stop BIG lumps getting in and violating the pump. :(

[mowgli]

what happens is that when the fuel level gets low, the remaining fuel sloshes about, collecting all the crap & suspending it in the fuel. when you stop, this crap then settles to the lowest available point, which is usually the pickup point.

pump fuel can have some right crap in it........ My dad once filled his lorry from a garage that had, overnight, received a delivery, and got 20 gallons of water as well as his diesel..

[meritlover]

crap and water is 2 separate issues. water will always collect at the bottom due to the densities.

fuel always sloshes around so iam not convinced by your argument.

the pick up point is no lower than the rest of the tank.

[Dod]

The pick up point is always inside the swirl pot which is filtered. I've stripped old cars and removed the intank pumps and theres never any issues with the filter content, and after that theres a second filter anyway.

That said, I found a Lucozade bottle in a Cav tank once. :s

[meritlover]

i found petrol in a petrol tank once. thought that was strange too.

[Dod]

I love that, I keep it and put it in my lawn mower. The poor sheep is usually sick for a week.

[hendrix]

nice explanation of potentiometer mr meritlover, i must agree with you

[Tidy Max]

your portentiometer description is impeccable meritman lol