Airlines have found a new way to save money on fuel. The Wall St. Journal last night reported on a booming business: Washing jet engines to remove the gunk that collects in flight and makes them run hotter. Those little fans that wizz all of that air through them get filled up with dirt and gunk and removing that saves fuel and helps the engines last longer.

Pratt and Whitney, a Connecticut jet engine maker, has developed a lucrative sideline business called EcoPower that uses atomized water sprays deep inside a jet’s turbines that washes them out, and then collects the dirty water and cleans it in a truck-mounted unit.

This small step has proven to be a big saver–according to Southwest Airlines, they’ve washed their Boeing 737’s engines 248 times and saved $1.6 million in fuel costs. It’s mostly because engines that are full of gunk run hotter and this means more wear and tear.

With the current frenzy over fuel costs, airlines are lining up, eager for new ways to save any way they can. It used to be prohibited at JFK, because the airport was worried about all of that toxic run-off. But EcoPower’s truck-mounted water treatment solves that problem, along with providing a way to run the engines cleaner and cooler.

Good news for the company: United has decided to wash its entire fleet twice a year, guaranteeing 3000 jobs for the company. United likes it so much that they are even going to wash their long-haul planes more, expecting that fleetwide, they’ll be saving three million gallons of fuel each year.