Subaru has built the world's first flat four-cylinder diesel for production cars. Europeans have been driving it in the Legacy and Outback since January, and in about a month, after the Paris Auto Show, they'll have it in the new third-gen Forester, too. Americans...well, we'll have to wait, but we could get the boxer-diesel Forester sometime in 2010. If, that is, Subaru gets the message (wink wink) that American buyers are seriously interested.

Yesterday I drove the new Forester 2.0D through the idyllic rural roads of Austria and neighboring Slovenia, and it's an appealing piece indeed. The boxer diesel is essentially an all-new engine, sharing its bore centers with Subaru's 3.0L gas six (to help reduce machining costs) but otherwise made mostly of unique parts. The twin-cam, four-cylinder mill displaces 2.0L, feeds off a common-rail fuel-delivery system, and breathes via 16 valves and a variable-nozzle turbo. Output is 145 hp at 3600 rpm but the engine makes a manly 258 lb-ft of torque at just 1800 rpm (compared with 226 lb-ft for the Forester's 2.0L turbo gas engine).

Subaru notes several advantages to the boxer's design. Most important, the horizontally opposed configuration is naturally balanced, requiring no weight- and friction-increasing counter-rotating shafts for smooth spinning. The engine is extremely compact, thanks to a bore pitch reduced 6mm over the 2.0L gas engine. An aluminum block minimizes weight, while a low-mounted turbocharger helps drop the car's center of gravity. The engine also wears a diesel particulate filter (DPF), a closed silicon-fiber honeycomb that traps particulate matter as it passes through the exhaust.

Mated to the new engine is a new six-speed manual transmission designed especially for the boxer diesel. Subaru currently has no automatic capable of handling the diesel's lofty torque output, and given the relatively low volumes anticipated for the diesel the company isn't inclined to spend big bucks on creating a new one. Expect the manual to be the one and only transmission offering when (if?) the Forester diesel eventually makes its stateside debut.

Official EPA fuel economy figures of course aren't yet available, but in Europe the Forester 2.0D is rated at an amazing 37 mpg city/highway combined. If you're a driver who likes to pour on the miles, here's your rig: With its 16.9-gallon fuel tank, the 2.0D has a range of more than 600 miles. Got a boat or a trailer? No problem. With the tank-like boxer-diesel, the Forester 2.0D can tow up to 4400 lb (compared with just 2400 lb for the gasoline-drinking, turbo 2.5L four in the Forester XT).

The engine lights off with a pushbutton starter and settles into a subdued clatter. You know right away it's a diesel, but the sound from beneath the hood isn't intrusive. Pull away from a stop and in a blink the turbo spools up and you're surging ahead. This isn't a quick car by any means: Subaru claims a 0-to-62-mph time of 10.4 seconds. Instead, think "stout." On an incline, the diesel powers up without fuss or undue shifting. On the autobahn, it hovered along at 90 mph with a refined thrum.