DETROIT -

When you fill your tank this summer, you might not be getting all the gas you pay for because of the heat. However, American drivers are fighting
back, and some gas chains are giving in.

We've watched gas prices go up. We've watched them go down. Drivers are held hostage by the ever-changing cost of something most of us can't live without.

Even worse, consumer advocates say sometimes you're not even getting the gas you pay for.

"It's a huge rip-off of American drivers," according to consumer watchdog Judy Dugan.

How heat and gas mix

Here's the issue: when gas gets hot it loses energy, meaning your car gets fewer miles per gallon. For example-- fill your tank on a 60 degree
day and the average car can go 500 miles. However, when you gas up, and it's 90 degrees- you get ten miles less from that same tank of gas,
but you're paying the same price.

Dugan said, "There's technology on that market that would fix it today."

That technology involves special mirrors on the pumps that adjust for temperature, so you get the correct amount of gas every time. Those pumps
are in use at 90 percent of the gas stations in Canada, but not here in the U.S.

Stations fight the change

In fact-- station owners have been fighting the switch to high tech pumps. They say customers benefit in cold weather, and the change would be too expensive.

"Put 2.4 billion dollars cost on gas station owners would only transfer that 2.4 billion dollars to the consumer." said Dan Gilligan of the Petroleum
Marketers Association of America.

Twenty one states, most in the south, have filed class action suits trying to force stations to change their pumps.

While some stations are still fighting, others are looking to settle, Costco has agreed to install the new pumps at its gas stations in warm weather
states. BP, Shell and ConocoPhillips say they're looking to settle as well, which could save you some money.