[relkeel]

Hi All

I was thinking about people warnings of running a car right down to the bottom of the fuel tank. They say that is where all the gunk and impurities gather, and letting this run through the engine could cause it damage. So I had the following questions for any techies or anyone who has actually experienced problems:

1. Isn't the pipe out of the fuel tank at the bottom, so there's going to be no room for gunk to accumulate as the petrol at the bottom will be sucked out of the tank first?
2. Doesn't driving a car reasonably energetically mean the petrol will slosh and mix around, meaning any gunk gets mixed and goes through fuel lines anyway?
3. Are Petrols a lot cleaner nowaday's, so this used to be more of a problem than it is now?
4. if it still is a major problem, does it impact certain types of engines or older cars more than newer cars?

Though everyone will apreciate the answers!

Alex

 

[archiegibbs]

Very good questions, I too have heard the same thing. The techie answers will be interesting as I am always telling my wife to top up her tank when the guage is on 1/4.

 

[Pete04222]

In answer to your questions:
1 - Yes. There is usually a small sump in there also. The pick-up tube has a screen on it also to prevent dirt and stuff from being picked up. But yes, fuel is always drawn from the bottom of the tank, not the top.
2 - No. If you did have junk in the tank and you start sloshing things around the junk will stay in suspension rather than just sitting in the sump. But normally there isn't a whole lot of gunk in there anyway.
3 - Yes. Refinerys are better, the materials used in storage tanks and transport hoses are better, and quality control is strictly monitored. Most places have regulations defining the quality the fuel must be to maximize efficiency and minimize pollution.
4 - Poor quality fuel would affect newer cars more than older cars by plugging up cats, ruining O2 sensors, gumming up injectors with the tight clearances, etc.

But on a car that is driven regularly, gunk and impurities is not usually an issue. Anything that makes it past the screen on the pickup tube is trapped by the filter. When a car sits for long periods of time gum and varnish can form in the fuel, but this does not just affect the fuel in the tank, it affects the entire fuel system and it doesn't matter whether the tank is empty or full. And like we said before, if there is junk in there it also doesn't matter whether the tank is empty or full.

The issue is condensation. When you have a large amount of air in the tank and the temperature drops below the dew point of the atmosphere in the tank then the water vapor will condense and droplets of water will form on the sides of the tank and since water is heavier than gas they will sink to the bottom. More air = more water. No air = no water. So with a tank near empty on a humid day and then it gets cold at night, the next morning you will be wondering why the car was so hard to start and why is it running so rough?

So whenever I store a vehicle I always make sure the tank is full and I add fuel stabilizer and run that through the system to prevent gums and varnishes from forming.

 

[Chrishawk4]

Great explanation Pete!

Any shell hats yet

Chris

 

[JazzyO]

W.r.t to point 3 - petrol quality varies over time but also by geographical location. From my own experience I can say that petrol in the 3rd world is definitely not up to 1st world standards, and may be worse than what US and European citizens put in their cars in the '70ies. Fortunately, my 550 has not had to experience that herself...


Onno



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[archiegibbs]

Great explanation Pete!


Chris

+1, very informative Pete. You should try to get a job in the petroleum/oil business

 

[relkeel]

Thanks Pete.

Managed to get 14.77 miles to the gallon from my first tank of petrol in the 550, although I didn;t realise fuel light comes on with still 8 gallons left in the tank!

Was mainly 60/70/80 mph driving on the M25 (forced on me by traffic) so that explains the good MPG.

About 10.5mpg from my latest tank, a bit more like it.

 

[archiegibbs]

Thanks Pete.

Managed to get 14.77 miles to the gallon from my first tank of petrol in the 550, although I didn;t realise fuel light comes on with still 8 gallons left in the tank!

Was mainly 60/70/80 mph driving on the M25 (forced on me by traffic) so that explains the good MPG.

About 10.5mpg from my latest tank, a bit more like it.

60 on the M25, that's good going. Whenever I venture south, it's always at a standstill.

 

[Dmitri]

Looks like Pete wins this one!

 

[Dmitri]

Oh yeah, and nice answer too!

 

[kk61]

Following Petes comment about condensation, this is the basis of the bottom of fuel tanks rusting out on cars that sit for a long time with low fuel levels.

Found out the hard way!

Kon

 

[Pete04222]

You should try to get a job in the petroleum/oil business

I've often thought about that Archie but I've got a pretty good gig going on right now. The outfit I'm currently with sends me to Singapore and gives me money to drink beer and chase Asian women. They haven't really asked me yet if I know anything about drilling oil wells. I'm not gonna press them, they're busy people you know. I'm pretty sure they'll tell me when they are ready for me to take the ship out. Until then, why rock the boat?

 

[Boxer]

Following Petes comment about condensation, this is the basis of the bottom of fuel tanks rusting out on cars that sit for a long time with low fuel levels.

Found out the hard way!

Kon

Which is why if you have to store a car, you should do so with a full tank and add stabilizer.

 

[archiegibbs]

I've often thought about that Archie but I've got a pretty good gig going on right now. The outfit I'm currently with sends me to Singapore and gives me money to drink beer and chase Asian women. They haven't really asked me yet if I know anything about drilling oil wells. I'm not gonna press them, they're busy people you know. I'm pretty sure they'll tell me when they are ready for me to take the ship out. Until then, why rock the boat?

Absolutely, why spoil a good thing Just keep away from the ladyboys

 

[Pete04222]

Absolutely, why spoil a good thing Just keep away from the ladyboys

You are sure right there Archie. It's kind of funny though, some of the best looking women in Singapore are actually guys. You do need to reach down and do "the check".

 

[Dmitri]

You are sure right there Archie. It's kind of funny though, some of the best looking women in Singapore are actually guys. You do need to reach down and do "the check".

Looks like the Cap'n has experience here...:rofl: