Engineers say that 60 percent of the energy used by a gasoline engine is wasted because of thermal losses from exhaust heat and radiator coolant.
By contrast, engine friction wastes just 3 percent.
Now, as consumers clamor for better fuel economy, suppliers and automakers are trying to reclaim some of that lost thermal energy.
Chrysler Group, for instance, uses heat from the 2013 Ram 1500's engine coolant to warm the pickup's TorqueFlite 8 automatic transmission to its ideal operating temperature. This improves fuel economy by nearly 2 percent, the company says.
Separately, supplier Tenneco Inc. is figuring out how to use recycled exhaust gases to generate electricity, warm the transmission and provide heat for the passenger cabin.
Gearboxes typically operate most efficiently when the transmission fluid is 180 to 190 degrees Fahrenheit, but on cold days, it may never warm up that much. So Chrysler and supplier Dana Holding Corp. figured out how to route the engine coolant through a heat exchanger to warm the transmission fluid, which has the viscosity of honey, during cold starts.
It's a balancing act, says Gregg Black, Chrysler's senior manager of advanced engine systems. The engine block also needs to warm up, so the system's computer must adjust the heat exchanger accordingly.
The heat exchanger, developed by Dana, is well suited for the Ram, and Chrysler may try it on other vehicles, too, Black said.
Dana also developed similar components to warm transmission fluid in the Ford Edge with a 2.0-liter engine. Ford says it improves fuel economy about 1 percent.
Tenneco, a Monroe, Mich., supplier, has spent the past decade finding ways to recycle exhaust heat. In 2002, Tenneco developed a space heater powered by heat extracted from the exhaust to warm the passenger cabins of commercial vans.
Tenneco marketed that device to European automakers until the vans went out of production, said Tim Jackson, Tenneco's executive vice president of technology.
Now, Tenneco is reviving that idea, and it has lined up development contracts with some unnamed automakers, Jackson said. Such a system would make use of 5 to 6 percent of a vehicle's waste heat, he said.
Tenneco also is working on two new ideas. The first would use recycled exhaust heat to warm transmission fluid. It's too early to estimate the likely boost in fuel economy, but Jackson says the technology should be ready for production in 2015 or 2016.
Tenneco's second new use of exhaust heat -- using a thermocouple to convert wasted heat into electricity -- may be the biggest challenge.
A thermocouple generates electricity when exposed to temperature extremes. Exhaust gases heat the thermocouple, while a heat exchanger provides the coolant. If Tenneco can improve the thermocouple so that it converts 3 to 5 percent, instead of 1 to 3 percent, of the waste heat into electricity, it would be efficient enough to recharge a vehicle's battery.
That, in turn, could improve fuel economy since the battery no longer would be recharged by an alternator powered by the engine.
That's the good news. The bad news: Researchers must cut the system's cost by 90 percent to make it commercially viable. Jackson predicts researchers will need another five or six years to develop it.
Engineers say as little as 14% of the energy in gasoline is used to propel a vehicle. Here's a sampling of sources of waste.
% of gasoline energy used
• Thermal losses, such as radiator and exhaust heat: 60%
• Wind resistance: 8%
• Rolling resistance: 5%
• Brakes: 4%
• Engine friction: 3%
Source: U.S. Department of Energy