Review: 2015 Volkswagen Passat TDI

Volkswagen’s diesel offerings have come and gone many times over the years, but they appear to be back for good. Unlike just a few years ago, nearly every model in the lineup is available with a TDI. Are these hybrid alternatives for the highway-dependent worth the price premium? We spent a few hundred miles in a 2015 Passat TDI SEL Premium to find out.
What is it?
The Volkswagen Passat has been many things over the years–an underdog, the enthusiast’s choice, an eight-cylinder sleeper–but at its core, it’s a good, old-fashioned midsize sedan. Our TDI is one of three different engine options. The others are conventional gassers–a turbocharged four-cylinder and a naturally aspirated VR6–and the diesel under the hood of our tester rounds out the field.

The Passat’s TDI differs from that found in Volkswagen’s compact models for reasons we’ll get to shortly. It’s a 2.0-liter, four-cylinder, turbocharged and common-rail-direct-injected diesel. It makes 150 horsepower at 3,500 RPM and 236 lb-ft of torque at 1,750 RPM and in our tester it’s paired to a six-speed automatic transmission. This combination is good for EPA fuel economy ratings of 30 mpg city and 42 on the highway.

As our testing time was spent largely on the interstate, we managed to do a little better than the EPA highway rating, averaging just over 44 mpg according to the multi-function display in the gauge cluster. We didn’t do a hand calculation, but we did manage nearly 800 miles before having to refuel, which backs up the computer’s claim.

So, what’s unique about the Passat’s TDI? It’s all in the exhaust. Unlike the Jetta and Golf/Beetle, the Passat uses a chemical after-treatment to reduce particulate emissions. This allows Volkswagen to turn up the wick a bit without running into the emissions ceiling present in vehicles not so-equipped. It’s added maintenance, sure, but relatively minor as such things go.

What is it up against?
The Passat typically competes directly with the rest of the midsize segment. Fellow niche competitors are found in the Mazda6 and Subaru Legacy. More mainstream examples would be the Honda Accord, Toyota Camry and Nissan Altima.

But the Passat TDI is a bit of a unique snowflake in that it’s the sole representative in the segment with a diesel engine. If you take that into account, the closest competitors would be the various hybrid options, as they tend to be more fuel efficient and thus, like the TDI, tend to carry a bit of a premium. But that’s not to say they compete directly, as diesel and hybrid cars tend to excel in different categories.

What does it look like?
Put all the Passats side-by-side and you’d be hard pressed to tell them apart. Our TDI model sports a badge identifying itself on the rear deck. As a SEL Premium model, there are some other flashy visual upgrades, such as a chrome grille and side moldings.

Otherwise, it’s standard Passat–conservative, classy and somewhat anonymous. It’s fine, if that’s your thing, but there’s a distinct absence of flair, even by German standards.

And the inside?
Our SEL Premium model sounds like it should be fairly loaded, but there are obvious blanking switches on the center console and the cabin, dressed in “Cornsilk Beige” feels airy, but empty.

The seats are relatively comfortable, holding us in place well enough for a full-tank highway excursion that took us up and over the Appalachians. Most of our interior gripes come from the control interface. The infotainment controls on the wheel are context-dependent, so if you shuffle around menus and absent-mindedly flip an arrow that previously controlled, say, song selection, you may find yourself scrolling through Nav destinations instead. Once you get used to it, it works well enough (except when the Navigation can’t find a destination it claimed to know, which happened to us a handful of times).

Our Premium model also came with some other niceties, such as an upgraded Fender audio system, a tilt/slide moonroof, and heated leather seats.

But does it go?
The Passat is a bit of a mixed bag in the “go” department. It handles competently enough and has a compliant ride, but it’s not what you might call “sporting.” It’s… mature? Less in the young professional sense than the AARP sense, feeling more like a golden-era Toyota Camry than an example of German precision.

But the TDI model is not meant to be a dynamic performer, so that’s forgivable. What makes it special is under the hood, so that’s where we’ll focus.

Let’s talk about torque for a minute. Horsepower is the most popular number to describe an engine’s performance, but it only tells half the story. Torque is the other half, but what exactly is it? Shade-tree physics alert!

Torque represents the “grunt” of an engine. Torque is the rotational force being delivered to the drivetrain via the crankshaft. Explosions in each cylinder produce force. That force pushes the piston downward. The piston pushes the connecting rod, which is connected to a pin on the crankshaft. This connection converts the downward(ish) force into rotational force, or torque. Multiply that amount by the number of cylinders that are applying force to the crankshaft at any given moment (it’s never all of them) and you have your advertised torque figure.

Home version: Stick your arm straight out in front of you, palm up. Pretend your arm is 3 feet long from shoulder to fingertip. Take something that weighs 1/3 of a pound and balance it on the tip of your middle finger. That’s 1/3lbs of force at the end of a 3 ft. arm, or 1lb of force for every 1 ft. of arm. That’s 1 lb-ft of torque being applied to your shoulder joint.

Mathematically, making more torque is easy. You just need more fuel and more air to make a bigger explosion. There are two ways to do that, whether you’re talking about a gasoline or diesel engine (forget hybrids for the moment): either increase the displacement or add cylinders, or utilize forced induction to supply more air to the engine. Diesel engines tend to employ the latter.

Horsepower represents how effectively (and more importantly, how efficiently) the engine can put that grunt to work. All else being equal (fuel type, aspiration, etc.), if you make the engine better at producing torque, you get more horsepower at the same RPM. There are many factors at play when it comes to the characteristics of an engine that contribute to its final torque and horsepower outputs, and we won’t get into them here, but suffice it to say that diesels, with their heavy rotational assemblies and energy-dense fuel, don’t lend themselves to being run at high RPM. So the trick to a good diesel engine is pumping a bunch of fuel into a few (relatively) large cylinders and using a turbocharger to supply enough oxygen-dense air for a nice, fat shove of torque.

So, if more torque comes from more fuel (rather than from, say, pixie dust), it should stand to reason that taking advantage of an engine’s thrust results in a mileage penalty. Thus, even in a forced-induction application, it makes sense to engineer the vehicle to spend as little time in boost as possible to maximize fuel efficiency.

Thus, in a (very) round-about way, we’ve arrived at a defining characteristic of the Passat’s performance.

It’s slow.

You may be thinking that a simple glance at the spec sheet would be enough to support this assertion, but when it comes to diesel-powered cars, there’s an illusion of speed brought on by the low-end grunt that can fool the driver into believing this is not the case. But it is. The power comes on as soon as you get into boost, then vanishes just as quickly.

The TDI’s torque band may look wider and flatter than the Colorado Plateau on paper, but when you actually need to summon all the go the engine has to offer, it can be an exercise in frustration. To get to that torque, you first need boost. To get boost, you need exhaust pressure. To get exhaust pressure, you need RPM. To get RPM, you need lower gears.

So, like the gutless wonder powering the Honda or Kia next to you, your TDI will ask the transmission for lower gears. And you shift. And you shift. And then you finally find the power. Then it’s gone.

If you’ve ever been behind a TDI that launched itself onto an on-ramp with gusto, only to find yourself braking to stay off its bumper before you reach the merge area, you’ve seen this in action.

The TDI then is all about expectation management. If you, as a buyer, put a priority on flat-road, long-distance cruising, then there is no better family sedan in this price bracket, period. If you want something that is genuinely fast and fun, you may want to take a longer look at the VR6 model instead.

Leftlane’s bottom line
A competent, fuel-efficient car that appeals more to the frugal than the frenetic. Buy it for the engine, not in spite of it.

2015 Passat TDI SEL Premium, base price: $33,585. As tested, $34,405.
Destination, $820.

Photos by Byron Hurd.