Okay, longer vehicle life and lower emissions. ALL gas, whether high grade or not, gums up after only a short time in the tank, that's wjy stations try to never run dry and fuel trucks constantly keep gas stations over the 1/4 tank level. This gum, a result of additives in the gasoline such as detergents and anti-knock additives create a sludge in the bottom of the fuel tank. This is why manufacturers say to never run your car dry and if possible, refill at 1.4 tank. If you do run a fuel injected car dry, you should always replace the fuel filter as it becomes gummed up with that sludge, as do the fuel rail, injectors, valves etc.
As far as fuel contamination, Canada does have slightly stricter guidelines than the Us, that's why it has always been 'sketchy' or not recommended for Canadians to buy Us gas. Unless it is REALLY cheap, and yuo full with super, many Canadians would rather stick to our gas. It was more important during the days of the leaded gas vs unleaded but still stands today for some.
ALL gasoline has additives, these additives are mainly detergents and some anti-knock additives, supreme gas has a higher amount of detergents in order to purify the fuel by killing contaminants, however in older cars, the detergents can actually eat away at gaskets and seals that are reliant of grime to hold together (even on a 5 year old car). this obviously causes leaks and expensive repairs.
As far as better mileage. If you run yoru car low on gas for extended period of time, or as a habit, you will pick up grime off the tank. This then clogs injectors, burns hard carbon deposits on the back of the valves causing them to remain partially open, clogs the fuel rail and slows down/impedes the injector pins, this causes a sick burn which also results in a clogged PCV valve and hardened vacuum hoses due to excessive heat. This not only results in poor combustion and greater emissions, it also means that you get poor mileage.
"I think you may be a victim of a myth on that one"
Actually I am a licensed mechanic, alternate fuels certified and a member of the Society of Automotive Engineers (SAE).
"Well it is impossible to keep the tank full but I guess safety costs like it always has
Again you may be a victim of a myth
Most of the time petrol needs to be compressed to explode"
Well your almost right. Fuel VAPOUR needs to be compressed in order to explode. You can toss a cigarette into a 5 gal pail of gas without the gas igniting, it will just put the cigarette out.
A quarter tank of gas running with a 7lb vapour lock gas cap is like a bomb waiting to explode. On impact it takes all of the cars millions of dollars in engineering to stop it from exploding. With a full tank, there is less vapour to compress and combust.
This is all high school automotive 101, thought, pretty basic stuff.
"Where does the fuel line leave the tank in your car?
Top or bottom?
Or if you like
At what level is fuel to low to be sucked from the tank?"
Depends on the car, but usually the pickup screen sits just above the bottom of the tank with one pump attached just above it. The pump outlet has spigot that fits through a locking cap that is usually at the top of the tank, though that again does vary by manufacturer.
As far as siphoning fuel, it depends on the restrictor placement and also if the tank is baffled In which case you'd need a robotic snake. Sometimes you can suck it dry but for that last 15 or so years, they have been getting better at thwarting siphoning.
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