Hi to All
I recall the tanks nestled in behind the front seat of my 1/2 Tons and me being a smoker oft wondered "Why Their?"
By Jim Kerr
A vehicle introduction a few days ago got me thinking about how vehicles have changed and even the simplest items can be an important part of the complete vehicle design. Take fuel tanks for example. We usually only think of them when the gauge reads low and there is no fuel station close by. Then you wonder: how large the reserve is? Does the gauge read right? What happens if I run out of gas?
My first experience with a vehicle fuel tank occurred when I was eight. Always interested in how things worked, I tinkered with and eventually disassembled a 1928 Chevrolet one-ton truck my grandfather had abandoned decades earlier. Getting at the fuel tank was easy on that truck. Tip the bench seat forward and there it was - bolted to the floor directly beneath the seat. Even into the 1970's it was common to find fuel tanks mounted behind the seat of a pickup, keeping it out of harm's way, but it didn't provide a very safe environment for the occupants.
Some of you may remember the problems the Pinto had with its rear-mounted gas tank. It seems that under certain rear end collisions, the fuel could ignite because of the position of the tank and the rear fuel filler. What is amazing is that there were many other vehicles of this same vintage that had similar fuel tank mountings and most survived with little problems. This safety issue did change the way vehicles were built however. Fuel tanks were moved inside frame rails and in front of the rear axle to better protect them in collisions.
In most passenger cars, the fuel tank is located beneath the back seat. There are exceptions of course: Porsche puts theirs in the front, but they also have the engine behind the driver. Some tanks are carefully contoured to fit into the tightest places. Tanks may be shaped to fit above the driveshaft, with half the fuel on each side. Removing these tanks involves more work, and they do need to be removed because most vehicles now have the electric fuel pump mounted inside the fuel tank. Ask any technician who has had to remove the two-part fuel tank from a modern Corvette and they would likely tell you they prefer having their fingernails pulled out rather than do it again!
So what triggered all this thoughts of fuel tanks? It's Honda's 2007 Fit subcompact hatchback. Honda engineers were looking to provide more interior space in the Fit and succeeded by placing the fuel tank in the unused space beneath the front seats. Unlike my old '28 Chev, this fuel tank is below the floor pan and meets the toughest crash test standards, but it does enable full use of the rear seat volume in this car. Honda took advantage by lowering the rear seat floor pan and building seats that flip up, so tall packages can fit into the vehicle - all possible because of a change in fuel tank location.
As for those unanswered questions, manufacturers do not build a reserve into the fuel tanks. They do design interior baffling and fuel wells to keep the fuel pump immersed in fuel so it will be cooled as it operates, but there are no specific reserves. If your gas gauge drops below empty and the vehicle still runs, it is just because of variances in calibration of the fuel level sender and gauge assembly. Don't rely on a magic supply of gasoline to get you to the next station. It's as easy to drive with the tank full as empty, so why not keep it full?
When you run out of fuel, the pump starts to suck air. No fuel pressure can be developed and the vehicle stops running almost immediately. You might have a few hiccups before it stalls but there won't be much warning. Fill it with fuel and it will start pumping again. A few people have concerns about an electric fuel pump inside the fuel tank, but there should be no concern. There is very little oxygen inside the tank compared to fuel vapours, so even if somehow a spark did occur, it couldn't ignite anything.
Finally, you may have noticed many newer cars take longer to fill with fuel. This is because the fuel filler pipes are smaller and are designed to create a venturi effect. Fuel flowing into the filler creates a vacuum that pulls the fuel vapours into the tank too. These vapours are stored in the tank or vehicle's charcoal canister until the vehicle is driven again. It may take a little longer to fill, but it is helping protect the environment too.