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Old 25th January 2013, 10:41   #1
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Question Letting your Car's fuel tank run empty? Drop the habit!

I am a very conservative kind of person & i usually let my fuel tank run empty before filling up. I keep a 2 litre gasoline jar filled with me for emergencies. Yesterday, i was asked by my mechanic not to do so. He said that doing so can harm the engine. He did not elaborate so i searched on the internet for this. I came up with the following.

Why you shouldn't let the car tank run empty?

1. Sediment from gasoline settles at the bottom of every gas tank. When you let your gas level run low, you force your car to use the dirtiest gas in its tank for fuel. The lower your car's gas level sinks, the more the dirt gets stirred up from the bottom of the tank. Drive on a near-empty tank and you risk this dirt getting into your car's fuel line and even into the engine. There's a good chance your car's fuel filter won't be able to catch all of it, especially if you drive with a barely filled gas tank on a regular basis. "You're going to pull the heaviest sediment into the fuel line," says Karl Brauer, editor-in-chief at Edmunds.com. "If it gets all the way to the engine, it could scar or damage internal parts of the engine." If this happens, you're putting extra strain on the engine. And you'll need to flush the entire fuel system if it clogs up with dirt. "You're talking a minimum of a couple of hundred dollars if it really jams up the system," Brauer says. At the very least, you'll need to replace your car's fuel filter more often. That will run you about $100. And if sediment deposits or sludge form on your fuel injectors, you won't like the way your car drives. "The car will run funny," says Tony Molla, a spokesman for the National Institute of Automotive Service Excellence. "It will feel like the car needs a tune-up."

Link to Source

2. The fuel lines, if starved of fuel, might allow air to enter which is not correct. Its like running engine without engine oil. Fuel Lines are lubricated by fuel. If not done they are going to harm it.

On the other hand, i came across this too.

Dear Terry,
With gas as expensive as it is, I've been driving my car until the gas light comes on. But this goes against everything my dad taught me.
He said to never let your gas go below a quarter of a tank, otherwise you could get dirt in your engine and ruin your car. Is he right, or does he just not want me to run out of gas?
-- Riding Dirty

Dear Riding,
Dear old Dad may have been right about many things, but when it comes to modern vehicles, he has this one mostly wrong.

Almost all cars have their fuel pumps installed inside the gas tank and the pump picks up the fuel from the lowest part of the tank, so you can get almost every last drop from the tank. If there is a lot of dirt and debris -- say, from a corroding fuel tank -- that gunk would normally settle to the bottom and be picked up by the fuel pump regardless of how much fuel was in the tank. But modern fuel pumps have a protective screen or porous sock-like cover that catches any contaminants before they enter the fuel system. And those small bits that might get through would normally be caught by a second filter closer to the engine. Back in the day, when manufacturers were churning out cars with very little rust protection, it was possible that after four or five years there could be some corrosion on the inside of the gas tank that could result in sediment. But most gas tanks these days are not prone to such issues. Where your dad may have been right is that you should always try to never run out of gas. That fuel pump inside the gas tank relies of the gasoline to keep it lubricated and cool, and if you frequently run out of gas you could cause the pump to fail. The good news is that the "low fuel" light comes on when there's anywhere from 1 to 2 gallons left, which is plenty to keep the pump safe. So it's OK to run the tank down to where the warning light comes on, but you should then get gas as soon as possible.


Link to source.


All this has left me more confused than enlightened. My questions are:

1. What according to you is correct?
2. Have any of the team-bhpians run into fuel-filter/fuel-pump/air-bleed problems due to empty tank?

Last edited by searchingheaven : 25th January 2013 at 10:43. Reason: Spelling mistake.
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Old 25th January 2013, 10:56   #2
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

I don't know what is correct, but while reading the article i was always having on the back of my mind the 'reserve' fuel i.e running your car till the time the low fuel indicator comes on and according to me it should be fine to run the car in with that. This was later confirmed at the end of the article, 'So it's OK to run the tank down to where the warning light comes on, but you should then get gas as soon as possible.'


I do not have much of daily running so instead of filling up the tank I usually fill it up for 1000 rupees and this is when the low fuel indicator turn on. However, having said that there have been times i keep my car running on low fuel as i know i do have around 3-4 L of fuel in reserve and should be sufficient for that drive. I would later fill up the tank either with 1000 rupees worth of fuel or tank it up in case the drive is long.

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Old 25th January 2013, 11:04   #3
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

What I don't understand is, once you fill up gas, it stays till you use it. (some evaporation happens, but then that is it) Why not tank up at 1/4th mark?

Why run the Car till the light comes on or you get warning beeps/chimes?

On occasions which are beyond your control, it is understandable. but otherwise...???

Be it my Car or Bike, I am yet to hit the reserve in both of them and have been riding/driving for over a decade now. It is not that hard to use and as an enthusiast, I usually keep all my energy (monetarily & the way fuel prices are going up) for refills. I don't have any reason for complaints which are beyond my control.

Last edited by Sheel : 25th January 2013 at 11:23.
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Old 25th January 2013, 11:39   #4
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Modern vehicles do have filters on the fuel pump as well as inline to the engine. So should not make a difference if you drive until the reserve light. But driving until stalling could cause a problem. Similar thread has come up today regarding a Skoda Fabia fuel pump failure:

http://www.team-bhp.com/forum/techni...ure-fabia.html
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Old 25th January 2013, 11:48   #5
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Quote:
Originally Posted by Maverick5490 View Post
So should not make a difference if you drive until the reserve light. But driving until stalling could cause a problem.
Dont have a reserve light. Ford Ikon 1.3 Flair.
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Old 25th January 2013, 11:51   #6
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Maintaining more than 50% fuel in the tank is the right method to keep evaporation losses to a minimum. Then fill as you run regime can be adopted which would eliminate all problems and hassles of going dry on the middle of the road.
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Old 25th January 2013, 12:04   #7
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

though not sure if less fuel in the tank more strain on pump, I always maintain 1/4 tank & keep filling like depending on the drive 500/=, 1000/= or full tank.
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Old 25th January 2013, 12:05   #8
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Quote:
Originally Posted by searchingheaven View Post
1. Sediment from gasoline settles at the bottom of every gas tank. When you let your gas level run low, you force your car to use the dirtiest gas in its tank for fuel. The lower your car's gas level sinks, the more the dirt gets stirred up from the bottom of the tank. Drive on a near-empty tank and you risk this dirt getting into your car's fuel line and even into the engine.
When the car is moving won't the sediments get mixed up with the fuel and will be present everywhere, rather than at the bottom of the tank? And if the particles are so big, I think it will be trapped by the fuel filter.
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Old 25th January 2013, 12:37   #9
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Nice article highlighting the risks of running dry. Apart from the risk of starving the pump of fuel, and introducing debris/contaminants into the fuel pump, which co-incidentally I was discussing on another Fabia pump failure thread just a few hours ago, it is a matter of convenience and peace of mind too.

It always beats me as to why many car owners don't simply tank up full everytime. It not only prevents cheating by bunk staff, but also lengthens the time between bunk visits. Instead of spending 500 Rs. 5 times, why not tank up for 2500 and prevent those 4 additional bunk visits? There is no extra money saved or lost with either method.

Quote:
Originally Posted by ArunV View Post
When the car is moving won't the sediments get mixed up with the fuel and will be present everywhere, rather than at the bottom of the tank? And if the particles are so big, I think it will be trapped by the fuel filter.
The fuel tank is a pretty big box (40-50 litres). When the volume of fuel is high in the tank, it is natural for the sediments to settle in the bottom. Unless the car is moving like a rollercoaster in all possible x,y,z axis movements , it is impossible that sediments settle anywhere other than in the bottom. Low volume has higher probability of sediments mixing with the fuel. Same reason why sugar added to a cup of coffee makes it taste sweeter when we are about to finish the cup.

jokes apart, I too am not sure about the sediments being trapped by the filter, or what impurity particle size escapes the filter and poses a problem.

Last edited by KarthikK : 25th January 2013 at 12:49.
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Old 25th January 2013, 12:48   #10
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Back to the root of the discussion, IMHO, I don't think that running with lower levels of fuel will cause any harm in terms of collection of sediments in the fuel line or pump or filter. The thing is that either you are low on fuel or have a tank-full of it, the sediments will always be settling in the bottom...apart from the slight mix up when the car is travelling (which can be negligible). The fuel out line is also at the bottom which ideally means that fuel from the bottom is only used regardless of the quantity of fuel in the tank which eliminates the sedimentation caused jam theory due to lower fuel level.

However, I must add that running low & ultimately stalling the engine will not be too beneficial for the engine! Not to mention that you might get stuck in the middle of the road which of course you will not want! Continuous flow of fuel also helps keep cool the fuel pump. I remember even my old Fiat 1100D AC fuel pump going bad after repeated fuel outages which resulted from a miniscule leak in the fuel line!

Regards.

Last edited by saket77 : 25th January 2013 at 12:51.
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Old 25th January 2013, 13:30   #11
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Quote:
Originally Posted by searchingheaven View Post

After reading all this, i will have at least 500 INR gas in the tank at all times.
In a few months, 500 INR should fetch us only 1 liter or 2

Jokes apart, here's a set of tips that I picked up from an email forward. I suspected it to be dubious, but my gas mileage has gone up by nearly 1 kmpl after I began following these tips. Hope they're useful and not considered spam:

- Only fill up your car in the early morning when the
ground temperature is still cold. Remember that all service stations
have their storage tanks buried below ground. The colder the ground the
more dense the fuel, when it gets warmer petrol expands, so buying in
the afternoon or in the evening....your litre is not exactly a litre.

- When you're filling up do not squeeze the trigger of the nozzle to a
fast mode. If you look you will see that the trigger has three (3)
stages: low, middle, and high. In slow mode you should be pumping on low
speed, thereby minimizing the vapours that are created while you are
pumping.

- Fill up when your tank is HALF FULL. The reason for this is, the more fuel you have in your tank the less air occupying its empty space. petrol evaporates fast.

- If there is a fuel truck pumping into the storage tanks when you stop to buy, DO NOT fill up--most likely the petrol/diesel is being stirred up as the fuel is being delivered, and you might pick up some of the dirt that normally settles on the bottom
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Old 25th January 2013, 13:48   #12
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Question Re: Letting your Car's fuel tank run empty? Drop the habit!

Fiesta does have a low fuel warning indication which appears when the DTE read 80 which means that assumably there is still 5 ltrs of fuel left in the tank and sufficient to make a run to the nearest bunk. I do the refulling normally when the indication comes on as this helps me calculate the FE.

Going OT: How often does one have to clean the fuel tank to eliminate the sediments accumulated at the tank bottom. Any ideas how the fuel tank are cleaned?
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Old 25th January 2013, 14:08   #13
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Quote:
Originally Posted by searchingheaven View Post
I am a very conservative kind of person & i usually let my fuel tank run empty before filling up. I keep a 2 litre gasoline jar filled with me for emergencies. Yesterday, i was asked by my mechanic not to do so. He said that doing so can harm the engine. He did not elaborate so i searched on the internet for this. I came up with the following.

Why you shouldn't let the car tank run empty?

1. Sediment from gasoline settles at the bottom of every gas tank. ...
Link to Source

2. The fuel lines, if starved of fuel, might allow air to enter which is not correct. Its like running engine without engine oil. Fuel Lines are lubricated by fuel. If not done they are going to harm it.

On the other hand, i came across this too.

Dear Terry,

...
Link to source.


All this has left me more confused than enlightened. My questions are:

1. What according to you is correct?
2. Have any of the team-bhpians run into fuel-filter/fuel-pump/air-bleed problems due to empty tank?

I dont want my fuel pump to get damaged by runnning dry. The sediment theory getting into the fuel lines dosent bother me much though. The Fuel Pump strainer does a good job of keeping the muck away - i got it cleaned once for my Accent after 4 years of use.

I get my tanks full all the time, except when I am not near my preffered fuel station in city, when the reserve light is on for around 20 KM. This is just to avoid multiple trips to the fuel station. There have been instances where I have driven cars beyond my comfort zone after the low fuel warning (around 40 KM for Accent, 25 KM for Estillo and 50 for Altis), but I try my level best to get the car tanked up after driving 20 KM in reserve.

With the ambassador, I dont remeber that we would have ever gone below the quarter mark. The thumb rule was - get it fuelled when the needle drops to half.

For my two wheelers, it was always 500/- of fuel once it was in reserve and I crossed my preffered fuel station. When I was in college, it was 100/- every monday morning - peteol was below 30/- a litre that time. I dont have a two wheeler for few years now, desperate to lay hands on one
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Old 25th January 2013, 14:22   #14
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Default Re: Letting your Car's fuel tank run empty? Drop the habit!

Quote:
Originally Posted by ghodlur View Post
Fiesta does have a low fuel warning indication which appears when the DTE read 80 which means that assumably there is still 5 ltrs of fuel left in the tank and sufficient to make a run to the nearest bunk. I do the refulling normally when the indication comes on as this helps me calculate the FE.

Going OT: How often does one have to clean the fuel tank to eliminate the sediments accumulated at the tank bottom. Any ideas how the fuel tank are cleaned?
That is an inaccurate way of calculating FE. As you know, the warning light depends on the DTE reading, which itself varies from time to time, based on driving style and traffic. The real test is tankful-to-tankful.

As regards me, I've seen the DTE light on my Fiesta only 3 times in the past 6 years. I invariably fill up after driving 250 to 350 kms. I do the same on the WagonR too, which has neither DTE nor low fuel light. And I've been doing this for the past 2 decades, including on my erstwhile M800.

On the other hand, my son drives the Figo till the tank is nearly empty. I discovered recently that the Figo has 3 warning chimes associated with low fuel apart from the warning light--they come on when the DTE is 80, then at 40 and finally at 20. I've heard the chimes at a reading of 80 and 40, but never dared till 20 reading.

Last edited by vnabhi : 25th January 2013 at 14:24.
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Old 25th January 2013, 14:30   #15
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Question Re: Letting your Car's fuel tank run empty? Drop the habit!

Quote:
Originally Posted by vnabhi View Post
That is an inaccurate way of calculating FE. As you know, the warning light depends on the DTE reading, which itself varies from time to time, based on driving style and traffic. The real test is tankful-to-tankful.
Venu sir,
I still use the tank ful to tankful method using the low fuel indicator as the reference point. I cant think of a situation when the indication comes up and the fuel in the tank can be more than the reserve fuel. If the fuel in the tank does not reach the reserve levels, the DTE will self correct and start reading more than 80 and the indication goes off. I have seen this happening. Pls clarify if my understanding is wrong.
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