running your car til it's empty - bad ?

Soldato
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Hi,

Have been told 2 things that running the car til it's totally empty is both good and bad ??

good in the sense that it cleans out all the rubbish from your car.

Bad that it's bad for your cat converter ?

Any truth to either ?
 
I would imagine that if there was any crud in your tank then it may well float on the surface of the fuel... so by running it dry you risk this crud getting into the engine. However if you fuel filter is working properly this shouldnt happen.

Other than that i dunno... i too have always heard its bad to run the tank dry. :confused:
 
No, generally it's percieved as a 'bad' thing as all the crap that can and usually does settle in the bottom of the tank can get drawn up and clogs, or obstructs, whatever filters your fuel system may have.
 
Bad idea - crud in bottom of tank will get into fuel pick up.

I had to spend a whole weekend cleaning out my carbs with an air line after running out of fuel once.
 
No, it's fine.

Most fuel tanks have the fuel inlet slightly above the bottom of the tank. Thus negating the crud problem.
 
I'm sure the 'crud in the tank' thing is largely a myth and that if you actually looked inside a tank you'd find that it's pretty much spotless.
 
kaiowas said:
I'm sure the 'crud in the tank' thing is largely a myth and that if you actually looked inside a tank you'd find that it's pretty much spotless.

It is. Anyone with a motorbike with a top mounted filler can tell you how much crud tanks have in them. There spotless. Tanks are lined and fuel these days are incredibly clean.
 
AcidHell2 said:
No, it's fine.

Most fuel tanks have the fuel inlet slightly above the bottom of the tank. Thus negating the crud problem.

the man makes a valid point. a lot of cars do have a slightly raised fuel intake. On medium-old diesels, or old petrol cars though, enough sludge can accumulate to mean that if you do run dry you'll take in a lot of sludge though. It usually just blocks the fuel filter on modern cars, but if the fuel filter isn't working right, it can cause a lot worse problems than that - fuel pump & injector type problems - big money and lots of downtime.

Also, you can get small amounts of water in the tank when you fill up - this is more an issue with diesels - which can build up over time.

It's not usually a good idea to run it till it's on fumes a lot, even if only because you might get caught with no fuel. If it's a diesel, running right to the bottom is NOT recommended - filters, and water drain plugs on filters are there for a good reason but they can only cope with so much abuse.

You do have the issue though, if you are always going round with >50% capacity, that you are using fuel to carry fuel.

My advice would be to not fill the car above 70% unless you absolutely need to, say, long journeys etc and not let it get below, say, 10% of tank capacity unless caught short - i've never had problems with fuel filters or anything to do with sludge (other than a couple of tanks i've had to flush) in 8 years of driving avg approx 30k miles a year in old petrol and old diesel cars, using this method.

If you want to clean all the gunk out of your car, get the tank flushed, and change your fluids and filters.

EDIT: and dont you believe it about fuel being clean. Petrol isn't as bad as it used to be but diesel cleanliness and quality can vary quite significantly.
 
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Skree said:
You do have the issue though, if you are always going round with >50% capacity, that you are using fuel to carry fuel.

But compared to the weight of the car and driver. It won't make a lot off difference to the mpg. I just brim it, then fill up when the tank is pretty much empty. Normally as I can't be bothered to stop for fuel earlier.
 
AcidHell2 said:
But compared to the weight of the car and driver. It won't make a lot off difference to the mpg. I just brim it, then fill up when the tank is pretty much empty. Normally as I can't be bothered to stop for fuel earlier.


It does make a difference though. 10 gallons of fuel isnt a light thing to carry, and if you're doing short journeys in town, you would find the difference increases.

I go by the rule that any difference is an unwanted one. If your local petrol station is like our local tesco one, always queueing for ages to get fuel, I can see the point in brimming it, or if you're going on a long journey.
 
Skree said:
It does make a difference though. 10 gallons of fuel isnt a light thing to carry, and if you're doing short journeys in town, you would find the difference increases.

Although all weight makes a difference, The hassle far out weighs *** tinny savings you make. for me anyway.
 
AcidHell2 said:
It is. Anyone with a motorbike with a top mounted filler can tell you how much crud tanks have in them. There spotless.

I guess you never owned a bike with a rusted out tank then? I've had loads of problems with fuel starvation and carb flooding caused by rust inside the tank of a couple of bikes in the past. Car tanks can also rust out. There is nearly always a small amount of water in fuel which settles out at the bottom of the tank.
 
Dogbreath said:
I guess you never owned a bike with a rusted out tank then? I've had loads of problems with fuel starvation and carb flooding caused by rust inside the tank of a couple of bikes in the past. Car tanks can also rust out. There is nearly always a small amount of water in fuel which settles out at the bottom of the tank.


Nope even the tank on my 1989 honda mtx was plated on the inside and had no rust.
 
I've seen plenty of tanks full of crud and seen a few cars stopped by sucking up said crud too, so saying "s' a non-issue" doesn't really work :D

Depends on where your fuel comes from too.......Seen some really crappy fuel full of debris from some stations.
 
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