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Can anyone settle an arguement my wife and I were having yesterday. Is it true that repeatedly driving the car when the fuel light is on and there is not much petrol in the tank is bad for the car. She has heard that all sorts of sludge gathers in the bottom of the tank and can damage the engine if it gets in. I think this is a myth for many reasons: surely any sludge will be mixed with the fuel in the tank as a result of the car's motion; there should not be much sludge in the fuel anyway and there is a fuel filter somewhere in the fuel line to stop any muck getting in.
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You're right, with modern cars anyway. There won't be much muck to pick up, and the pick up pipe rarely sits in the "sump" of the tank in any case. With older cars (10 - 15 years plus), particularly if they've been standing, you can pick up bits of rust and dirt which will quickly clog the fuel filter and pipe. It depends how rusty the tank is inside. My mother would always drive on empty as a theft prevention tactic - she reckoned if anyone nicked the car they wouldn't get far!
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I think that you also have to be aware of condensation in the tank which will result in a water build-uo in the bottom of the tank.
Just had to have a motorcycle tank repaired due to rusting from that cause.
As a precaution I would advocate draining and cleaning any tank once about every six years.
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Personally, I think its out of date too.
I have looked inside many tanks when removing the level/sender/pump on top to reveal quite a big hole which you can look in with a torch, they have all been shiny silver with no debris, I have only seen rust on a Suzuki Motorbike, never on a car, and nowadays they have plastic tanks anyway.
The fuel pickup is sually near the bottom, but not so close it causes flow problems, but as foreign objects would be on the bottom, and so id the pickup, I don't see how the level will affect this as bottom is bottom no matter what's above it.
The pickup has a fine mesh screen which is continually washed anyway, so as bits do get on it, they are washed back off...then any that get through are picked up by the disposable fuel filter.
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I once had a colleague who had a company owned Ford Granada 2.9 injection circa 1990. Car was around 3 years old with 70k ish miles.
He ran out of petrol on the motorway.
A monthlater the entire fuel inmjection system had to be stripped and cleaned/replaced to solve a persistent misfire which started the day after he ran out of fuel.
madf
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A monthlater the entire fuel inmjection system had to be stripped and cleaned/replaced to solve a persistent misfire which started the day after he ran out of fuel.
I had to have all the fuel lines blown through on a carb car after running out of fuel. The misfire started within 20 miles. It was one of my classics, so I'm sure it was rust or water in the bottom of the tank.
Again, I think its largely a myth on very new cars, but I don't take any chances on my '96 Mondeo.
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My Mk4 Escort had done 55k when it ran out of fuel. Didn't cause any problems and was back on the road again once I'd put the "spare" petrol in from a can in the boot. I was surprised as the car had never been allowed to fall below half-way on the fuel-guage by the previous owner. I have had a couple of upsets of miss-fire, including the morning before it ran out when it just wouldn't start, even with a lengthly push! But these seem to clear by themselves.
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If there is only one feed from the petrol tank to the engine, why does it make any difference what quantity of petrol is in the tank?
i.e. if the feed is near the bottom of the tank, then whether or not it picks up any sludge is independent of the petrol level.
I was shocked at the filth that came out of the fuel filter when I changed it - is this normal?
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Logically I can't see why it should make any difference however much sludge there was in the tank. What is the sludge doing when the tank isn't nearly empty - mixed up in the petrol, being sucked through, or sitting on the bottom waiting to be sucked through?
Nonetheless people do report fuelling problems after running the tank right down, so there does appear to be something in the theory.
May be as the last few drops gurgle out, mixed up with a lot air, it creates abnormal turbulence in the tank which dislodges scale that otherwise stayed put?
Incidentally diesel is much more prone to the problems of condensation, and it is good practice, at least in marine use, to drain the tank entirely every year to eliminate accumulated water.
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Well with aircraft (in the RAF at least) the fuel tanks are filled after every flight, to ensure that condensation can not form, due to lack of space.
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Good point about marine use. I checked my narrowboat tank after two year's use and found about 10% of its full volume was water. Luckily, this was before a hairy passage down the Bristol Channel, from Sharpness to Bristol, when a breakdown could have been disastrous.
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My Mk4 Escort had done 55k when it ran out of fuel.
A world economy record?
I'll get my coat ......
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I am surprised that no-one has mentioned that most fuel tanks on modern cars are now made of 'plastic' rather than metal. This obviously eliminates the problem of rust forming in the tank and flaking off in later life.
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Don't be surprised - read the posts more carefully!
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As new fuel systems are sealed cant see any prob.water cannot get in if it does its in small amounts not enough to worry about.sludge isnt a prob as it used to be so why worry.in respect of filtering its unlikely any debris will get through if filter changed on regular basis should not have a prob?
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As new fuel systems are sealed cant see any prob.water cannot get in
Doesn't petrol contain a certain amount of water anyway?
Also, depending on how low the holding tanks are at the service stations, won't their tanks also suffer condensation?
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Systems can't be totally sealed - as a full tank gets used, air has to be drawn in from outside to fill the space. That air will contain water vapour, and if the inside of the tank is cooler than the air drawn in, then the vapour will condense.
I don't know the water goes though - it doesn't normally seem to be a problem.
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