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 Dodge Ram'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.
"It's a trade-off," Black said. "You have to be careful where you put that energy to make the best use of it."
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 equipped with a 2.0-liter engine. Ford says it improves fuel economy about 1 percent.
Recycling exhaust heat
Tenneco, a Monroe, Mich., supplier of catalytic converters and exhaust systems, has spent the past decade finding ways to recycle exhaust heat.
In 2002, the company 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 -- instead of engine coolant -- to warm transmission fluid.
Jackson says this technology should be ready for production in 2015 or 2016, and he speculates that automakers could market it as part of an optional cold-weather package.
It's too early to estimate the likely improvement in fuel economy, but Jackson says the additional hardware would not be overly expensive.
Tenneco's second new use of exhaust heat -- to generate electricity -- may be the most challenging. The company is experimenting with a thermocouple that converts 1 to 3 percent of the wasted exhaust heat into electricity.
A thermocouple generates electricity when it is exposed to extremes of temperature. 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 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 is that researchers will have to reduce the system's cost by 90 percent to make it commercially viable.
Jackson predicts the researchers will need another five or six years to develop it. "Tenneco is in advanced study" of the technology, Jackson said. "We are still doing computer simulations. We are pretty happy with our progress so far."