Gas tanks used to be pretty simple devices.  Basically, they were a big metal box that gasoline was stored in.  And that was a good definition of a gas tank for quite a few decades, at least until the advent of emissions regulations.

In the early 1970s, the Environmental Protection Agency (EPA) did some testing and discovered that the vapors that escaped from vented car gas tanks made up a significant portion of a car’s overall hydrocarbon emissions.  As a result, in 1971, the EPA mandated that all vehicles needed to have sealed systems so that volatile gasoline vapors couldn’t escape into the atmosphere.  The solution, as designed by most of the car manufacturers, was to vent the excess vapors into charcoal canisters.  From there, the vapors are periodically purged to the engine, where it is burned along with rest of the fuel.

But sealed off systems, such as those discussed above, have many components.  Besides the fuel tank, there are lots of hoses, valves, filters, clamps and other things that make up the gas delivery system. And, unfortunately, a tiny amount of fuel still escapes.  Automotive engineers refer to this as “permeation” and it is well regulated by the EPA. The EPA’s current “Tier II Bin 5” passenger-car standard allows for a maximum leakage of 95 milligrams per day. To achieve California Air Resources Boards (CARB) really tight Partial Zero-Emission Vehicle (PZEV) rating, a tank must emit just 20 milligrams a day.

For this reason, according to Lynch Chevrolet in Mukwonago, WI ,starting in the early 2000s, most PZEV-capable vehicles have employed steel rather than the preferable, light-weight plastic fuel tanks for their superior permeation resistance.

But TI Automotive, which supplies gas tanks nearly every automaker around the globe, came up with the first weight-saving plastic tank to earn PZEV status. This is a significant advancement for car manufacturers who obsess over every pound that is added to a new car design.

TI’s PZEZ tank, which was first launched about 10 years ago, relocates all the fuel-delivery components (fuel pump, piping, etc.) which were the source of the most significant leaks, from outside the tank to the inside. In addition, the plastic, which is blow-molded around the other components in a process that TI Automotive calls “ship in a bottle,” is constructed of six separate layers of plastic. Today, TI says that roughly 75 percent of American vehicles have plastic tanks. And, compared with a similar steel tank, TI claims its plastic tank five pounds, lighter.

There is one drawback, though. The most common complaint that the car manufacturers hear about the plastic tanks is that with many hybrid cars, owners can hear the fuel sloshing about when running in electric mode!  This unwanted fuel-slosh noise is made noticeable because hybrids are running farther and farther in electric-only mode. TI is hard at work solving this problem with additional baffles and shielding so the gasoline noise is kept to a minimum.

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