Don't want to be totally ignorant here, but how exactly does a fuel tank work - everyone says don't run down the fuel tank to empty or you will pick up all the carp from the bottom of the tank. But surely the pipe from the tank must be at the bottom of the tank? Or is it slightly higher in which case how would the carp get from the bottom of the tank up into the pipe?
Don't laugh at my ignorance please!
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I'm guessing that the amount of carp remains reasonably constant, but the amount of liquid becomes less, increasing the concentration of carp and the likelihood of sucking it up.
Having said that, during many years of being poor, I ran cars down to fumes or out of petrol completely and never suffered any rubbish in the carb - not that I noticed, anyway.
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I've twice had to strip and clean carbs when friends have let their cars run out of petrol. Another trick to suck the carp out of the jets if the engine will start is to remove the air filter and place your hand over the air inlet, thus restricting the diameter and increasing the velocity of inrushing air. Careful doing this, don't seal the gap completely, or if you do, don't balme me for the pain.
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I read often, only post occaisionally
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Pipe to feed engine should be above the bottom of the tank but this does not guarantee that any carp doesn't float on the surface, or get sucked into the pipe - especially when vehicle is at an angle e.g. going uphill. NB If there is little fuel in the tank, it will slop around and stir up any debris.
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Ivor - I believe a tank also has baffles to stop surging?
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Most but not all tanks have baffles, but this does not stop the sloshing which stirs up the debris.
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Ivor - I should think the baffles help to stir things up.
And I forgot to mention the effect (rare over here, but more common in Canada) of fuel starvation caused by an inch-thick block of ice at the bottom of the tank.
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It depends what you mean by 'empty'. It is probably impossible to run an engine till the tank is truly empty, as the outlet is probably not at the lowest point. Everything sinks in fuel: grit, water, carp generally. If there is enough carp it may get into the float-tube for the gauge-sender, causing it to stick and give false readings - then you *may* run the tank dry (it happened once to SWMBO).
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Everything sinks in fuel: grit, water, carp generally. If there is enough carp it may get into......it certainly can.
Many years ago I filled up with what I think was the very bottom of a filling stations tank and thus payed cash for some water.
Much later the fine rust from my tank blocked the fuel line and the tank started to loose fuel. No one would even consider patching the tank and the car was too new to get a scrap one. So a full price new tank was installed.
I hope and assume that this is a rare happening because it was a very expensive exercise apart from the breakdowns. I cannot recall if I ran the tank low in those days but I certainly would not do it these days.
The fuel filter was just a crude mesh in the carb.The fuel line was a real pain to clear. I guess the filter by the tank avoids the aggro I had.
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Apart from the inconvenience of getting air in the fuel lines, and having to prime the system (especially a diesel), I'm not sure why people feel what comes from the tank is cleaner when it is full or nearly empty? The crud is still at the bottom, either way?
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Fuel tanks have swirl pots where the pickup 'collects' the fuel to ensure it stays submerged in relatively 'air free' fuel.
There may also be baffles to avoid fuel surge (as has been said previously)
Plus a (usually) rather over-complex breather and fume recovery system!
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Apart from the inconvenience of getting air in the fuel lines, and having to prime the system (especially a diesel), I'm not sure why people feel what comes from the tank is cleaner when it is full or nearly empty? The crud is still at the bottom, either way?
I agree - I can't understand that point. And if the pipe did go right to the bottom, it would pick up the dirt even from a full tank?
Old cars like my Triumph 2000 have a glass goldfish bowl with a mesh filter attached to the fuel pump. If any other freshwater fish gets in I can release the clip and clear it out.
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Years ago before the days of fuel filters and plastic tanks, all sorts of crud used to build up in the fuel tank. Water and rust flakes, etc. Volvo used to use cork sealing rings on the filler caps, they used to break up and end up in the tank. With a full tank all of this stuff swilled about and didn't stick to the crucial part - the little strainer on the end of the fuel pickup pipe. With a low fuel level all of the crud was concentrated around the strainer - which became blocked ! After an hour or so the stuff might fall away and enable the fuel to flow again - for a short while. A couple of gallons of fuel usually washed it away.
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