One of the economy tips given recently is keeping your tank low on fuel to save weight. I was telling someone this, and he recounted that famous motoring old wives tale that "running your tank on empty brings the muck out of the bottom of the fuel tank". Whilst I've heard it repeated many times over the years I've never believed it.
As a teenager my tank was always run on dregs, fuel going in £5 (or less) at a time. These days I run from full to dregs to spare the pain of filling up.
In 28 years of driving in 25 different cars I've never had a problem with dirt in fuel so is it time to consign this piece of "wisdom" to the bin ?
Edited by *Gongfarmer* on 23/07/2008 at 16:29
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Yes.
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Why wouldn't the engine's fuel filter catch any debris that may be lurking ?
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I had a Fiesta (1990 H plate) that suffered from this. It was running on dregs when I first got it. Iit would hop down the road when it had the problem. In the end my friendly garage cleared out the system with liquid and fitted an inline fuel filter. Problem went away.
So on a 6 year old car I certainly suffered from this and it wasn't nearly empty when i was running it but it was running on vapours when I test drove it.
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I emptied out an old Morris Minor fuel tank - lots of sugar, some rust and other rubbish. No problems with the thing running!
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It is possible that there could be so much grunge in the tank that it could block the filter. Beynond that I don't see a problem, particularly with plastic fuel tanks rather than mild steel = rust flakes!
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Why wouldn't the engine's fuel filter catch any debris that may be lurking ?
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Things may have improved in recent years.
A long while ago, I took on some water when, I guess the filling station tanks were low.
It rusted my tank, filled the fuel line with rust powder and it got through into the carb bowl.
In the end I got serious fuel starvation and had to get a new tank and the system "blown " through.
I am not sure if an in line filter was fitted but it certainly got through the fine mesh filter at the carb.
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One of the economy tips given recently is keeping your tank low on fuel to save weight.
The amount you save you will probably use going to and from the fuel station every day.
Not sure about potential damage from running on low but it won't do the engine any good if you run out, which you are increaseing the risks of if driving around on dregs.
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Breifly modern cars have counters on the fuel caps! & calculations are made to fuel monitoring based on how many times the fuel cap is removed & refitted. They vary on various makes but I have known a large well branded car to bring a dealer on its knees only to discover months later that the guy had refulled £5 at a time ( mangement system thinking car drinking fuel ! )& the management system kept weaking off the mixture so much so that it misfired more than it fired! this problem has now been resolved with software download.
CR diesels will suffer with air going through the pumps if the fuel runs too low & can shorten their life considerably!
Injection in tanks pumps are cooled by fuel so when it gets low they run hot!
Most manufactures recomend in their handbooks leaving 20 ltrs of fuel in a tank!
rgds
I Doc
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Breifly modern cars have counters on the fuel caps! & calculations are made to fuel monitoring based on how many times the fuel cap is removed & refitted..... ( mangement system thinking car drinking fuel ! )& the management system kept weaking off the mixture so much so that it misfired more than it fired!
For the reason you outline, I can't imagine this is very useful, i.e. monitoring how often fuel cap is removed. If the software governing how rich/lean to make a mixture is (at least) partially governed by this method I'm surprised there aren't more problems apparent & reported. Surely the parameters to cope with 'filling-up' patterns would need to be so wide that nothing useful could be deduced?
On the general point - I could imagine constantly running with just a few litres could produce more 'waves' with little fuel moving around a big space - this could well, one imagines, stir up more sediment & overwhelm or clog filters so reduce fuel flow etc.
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I keep mine tanked up - habit from 2001 when I was made a victim of the so called fuel blockades, which in my opinion, was the result of self centred egotism.
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The trouble with refilling often with a small amount of fuel is that on an old steel tank (corroded internally through condensation) is that it constantly swirls up the brown sludge which then lies in suspension ready to be drawn through to the engine. It takes an hour or so for the sludge to sink back to the bottom of the tank after filling and of course no one stays at a petrol station for an hour to let it settle.
This can suddenly start to be an issue (dont know why suddenly - just started to happen to me one day) and cause your car to grind to a halt about 2 miles from the filling station. I would not totally trust a fuel filter to catch all of the sludge as I have subsequently found traces of brown powder residue in the carb float bowl.
The only long term solution is to flush the tank, keep it full to avoid condensation thus corrosion and fit a filter.
Most modern cars have plastic tanks so this phenomenon generally only occurs to the older car.
BTW what cars have counters on the fuel caps?
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Since you didn't respond 'injection doc' to my querying of the fuel-cap 'counter' & having found no mention or trace of this googling, I must assume it is indeed a an invention yet to find a purpose - or indeed, yet to be invented at all!
There are fuel cap sensors, but they don't measure on-off cycles, merely vapour pressures & such like - or absence of cap.
Edited by woodbines on 24/07/2008 at 00:38
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Doc
What was that on? New one to me; I've only seen cap sensors on a FAP-equipped car? Why wasn't the HEGO flagging a LTFT issue?
Some of the CRs will now first go to limp and then cut the engine before it runs out to protect the pump.
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needless to say it was french & a top of the range car. The magnetic sensor is related to FAP's on diesel's but petrol cars now have them & they can be a pressure sensor on the tank. Your right the LTFT should flag a fault but the software conflicted!
Some of the CR;'s do indeed now delibratley induce a misfire when the tank is very low & some even turn the AC off to conserve fuel but rumor has it ( and from a very good scource) that low fuel could contribute to the TDCi problem. Big flat shallow fuel tanks don't help
I Doc
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Doc
"The" TDCi problem?
Shouldn't that be "one of?" Was that the "Failure of the rollers to bed in" problem; the flimsy con-rods, or the regraded injectors that need software correction?
Yes; flat tanks, allied with no primary pump, could indeed have an effect.
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Injection Doc, Screwloose -- genuine question.
Could the "TDCi problem" happen if you run the car on fumes regularly, even though there's a fuel filter?
Obviously a filter can't trap every particle, it will just trap 99.5% of debris or whatever. So is the idea that running the tank low regularly, will send more debris to the filter, and increase the chance of muck getting through to the high-pressure pump etc?
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The danger of running a TDCi low on fuel is air getting into the HP pump and it running dry.
Debris/water will be dealt with by the filter - just not an issue these days. [Carburettors? What they?]
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So where does this gunge come from in the first place ? I would have thought the refineries worked to very high standards of cleanliness to protect what must be a very substantial investment in equipment ?
On the topic of refueling frequently in small amounts, Is it true that an amount of pollution is caused whenever the (petrol) filler cap is cracked open. I seem to recall somewhere (Germany?) a large sleeve/bellows affair that sealed the area around the filler neck and hoovered the fumes away?
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Its a load of nonsense these days, with plastic tanks, and large screens on the pickup, and inline fuel filters. Any muck in the tank will sink anyway, so it will always be around the bottom. A car sip tea from the top of a cup with tea leaves at the bottom.
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"Its a load of nonsense these days, with plastic tanks, and large screens on the pickup, and inline fuel filters. Any muck in the tank will sink anyway"
Try telling that to customers who have had to buy new intank pumps where the filter screen has totally blocked & the pumps ground to a halt!
I Doc
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cars are fitted with EVAP systems now where the fumes are drawn of the tank to a charcol canister & the canister is purged by using the vacum in the inlet manifold normally around 3000rpm & ECM controlled. The engine then burns the excessive fumes off. So when you open the tank there is only a small amount of vapour.
Most of the vapour comes from the actual fill & in some countries is drawn off by a rubber sleve on the filler pipe.
I Doc
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I saw some in the States - rather cumbersome.
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The question should be "Why are we breathing benzine when we fill up?" It causes leukaemia - no question.
There's no safe exposure limit and extraction equipment would be required by law if the same process was carried out in an industrial environment. You can't expose employees to even one part per billion.
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??Does running your tank on empty cause problems ?<<
Only for any "toe=rags" that manage to "nick" your motor! - means that they've to spend some of thier money om fuel if they are going to take it any distance, which may help to leave a "traceable" trail, cctv cameras, being recognised etc. - besides it would do thier street-cred no good to be seen pushin a motor!
One of the best anti-theft devices is an empty tank!
Billy
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I don't see how a bit of gunge, lurking about in the bottom of the tank, knows how much fuel there is above it. If it is near the outlet pipe it will be sucked out anyway.
I'd have thought cornering and going over bumps would slosh everything about anyway.
If tanks had floating intakes it might be true, but they don't?
Any reported problems would much more probably be down to air locks and the need to reprime some systems.
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The people that run on empty and runout on a corner of the road give me problems.
Local filling station - driver comes in daily and buys up to £5.00 - some days less- enough to put the petrol light off and get to & from work.
Cutting matters fine in my opinion.
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I don't run around on empty, but I always refill when the light comes on, or when the gauge hits the red. It never seems to have caused any problems on any car I've had.
Cheers
DP
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Car fuel tanks are plastic, but petrol station tanks are usually steel. They can rust, let in water, and let out fuel. As well as collect sludge, which can be stirred up on delivery, especially if the franchisee lets stocks run down, or doesn't pay for tank cleaning, except on an emergency basis. Double skinned tanks with inter-skin (interstitial for the fussy) monitoring are an answer, but they are not universal by any means. So, those without have to monitor. More than you want to know here: tinyurl.co.uk/pe4t This might be out of date but it gives the gist.
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i used to fill up to the brim when ever i filled up but now i rarely put more then £20 in at a time and i havent had more then half a tank in about 2 months but im finding im actually saving a bit by doing it that way im not sure why whether its weight or what i dont know but im by no means saving a small fortune but these days every penny counts
Edited by welshlad on 24/07/2008 at 15:35
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My Shogun has a steel tank that had rusted through and contaminated the fuel pipes.
And I think it *might* have run out of fuel, despite the fuel gauge showing 1/4 tank left. It started running down on power, and then cut out going up a hill....
So, jerry can in hand I'll be trying to get it going at the weekend!
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