What if they stopped for gas?
"Why are you stopping for gas, the gauge says it's ¾ full?" Jo asked from the back seat.
"Old car, the gauge is broken, I go by mileage," Dean asked and gave Sam a warning glare at his confused look. "Maybe you ladies should you the facilities."
Ellen got out of the car without a word and Jo followed after shooting the boys an apologetic glance. Dean got out of the car, but as soon as Ellen and Jo were inside and out of sight, he hopped back in and started driving off.
"What are you doing?" Sam asked.
"I'm not going to put up with the silent treatment for 2,000 miles," Dean replied.
"You do realize we can never go to the Roadhouse again," Sam said, regretfully, as Dean shrugged and cranked the music.