The Lexus HS 250h is the first luxury hybrid sedan that doesn’t have a non-hybrid version (think Lexus RX 350 / Lexus RX 450h for an example of a non-dedicated hybrid), and like the Toyota Prius—which has no non-hybrid equivalent—it feels different than its Lexus stablemates.
The Lexus HS 250h shares the fundamentals with the other parallel full-hybrids from Toyota/Lexus with a gasoline engine, continuously-variable transmission and an electric motor that can power the vehicle either alone or in concert with the gasoline engine. The HS 250h is front-drive only.
The engine in the HS 250h is part of a system all tuned to maximize mileage and minimize emissions. It has a 2.4-liter Atkinson cycle—primarily defined by a “late” closing of the intake valve compared the traditional four-stroke cycle, plus long stroke and high compression ratio—four cylinder engine rated at 147 horsepower, and a 140-hp drive motor (another electric motor serves as generator, engine starter and controls the transmission ratio). Altogether it’s rated at 187 total system horsepower, not higher because it’s not additive. Power peaks occur at different rpm. It meets California SULEV and federal Tier 2 Bin 3 exhaust emission standards.
The power system—it can’t be called just an engine—includes a number of different efficiency factors, such as combining the aluminum engine radiator, hybrid system radiator, air conditioning condenser and fan into a single unit to reduce weight. The oil pump for the transmission is electric, saving parasitic drag for when it’s not needed.
Lexus also took pains to control engine heat, keeping it from recirculating into the engine air intake for improved low speed an idling performance. Additionally, the Lexus HS 250h has exhaust heat recovery, which recycles engine exhaust heat for faster warm-up and more efficient operation in low ambient temperature conditions, something that is a problem for hybrid vehicles in cold climes.
The Lexus HS 250h also squeezes out more mpg via improved aerodynamics. The five-passenger—actually, more like four-plus-one—four-door sedan has a drag coefficient of 0.27, matched by very few other production automobiles. The most obvious feature is the blanked-off grille, but Lexus body engineers smoothed body transitions, added subtle spoilers and overall shaped the vehicle to slice through the air more cleanly.
Acceleration to sixty miles per hour takes 8.4 seconds, not that we would know from a 9.2-mile hypermiling “test drive” that included feather-footing and working the drive-mode switch, which has four modes, Power, Normal, Eco and EV. The first three set the responsiveness of the throttle opening, though not the maximum output. Think of it as a foam pillow betwixt foot and gas pedal.
The EV mode is what it sounds like: Electric Vehicle. It allows the HS 250h to be driven solely under electric power up to about 20 mph or until the gas pedal is pressed too hard. We used that as much as possible.
We also watched the power gauge to the left of the speedometer, where a tachometer would otherwise be. The dial is marked in four colors, blue, dark green, light green and white. When the needle is in blue, the HS 250h is in charge mode, as when coasting or braking. The needle will swing from dark green to light green to white—“power”—progressively as the accelerator is pressed harder. Obviously, staying in the green is how to get better gas mileage.
Stay in the green we did, even it meant slower acceleration than those behind may have wanted. Really, the sound waves from their horns could not have added all that much fuel savings, though we appreciated the assistance. We also liked the people who told us we were number one by holding up a single finger, even if it weren’t the one we would have used. This may have been a local New York custom, however, so we told them they were number one with us too!
Just kidding, though our slower than usual pace probably—definitely—annoying. We coasted up to traffic lights, timing them as closely as we could. We let off the gas when approaching the crest of a hill, making up speed on the downhill side. We conserved momentum whenever we could.
The most difficult part was the final leg on a long winding private drive—all uphill. We pressed the EV button, kept a light touch on the throttle and stayed in electric drive until about thirty yards from the finish, when we felt the gasoline engine restart. Our final mpg reading: 46.2 mpg.