GCC recently had the chance to get behind the wheel of several 2015 Jetta TDI models along with other VWs. However, given our recent look at the Chevrolet Cruze Diesel (the contender, earlier post), we wanted to focus on the latest version of the US diesel leader. The bottom line is that the 2015 Jetta TDI enjoys a double boost. It benefits from model-wide improvements in exterior, interior, and features; and especially benefits from the new diesel engine, with its improved fuel economy, performance and refinement.

The EA288 under the hood. Click to enlarge.

The EA288. The EA288 is based on the Volkswagen MDB, its modular diesel engine toolkit (Modularen Diesel Baukasten) (earlier post). The new EA288 engine will eventually replace all the 2.0-liter diesels currently fitted in Audi and Volkswagen TDI Clean Diesel models. This turbocharged, common-rail, direct-injection four-cylinder engine makes 150 hp (112 kW)—an increase of 10 hp over the prior engine—and 236 lb-ft (320 N·m) of torque. This powerplant shares only the bore spacing with the previous diesel engine that had the same designation.

It is one of the most fuel-efficient engines in its class, and already conforms to the LEV3 emissions standard in the US.

Fuel economy improvement
	2014 Jetta TDI	2015 Jetta TDI	% Δ
City mpg (l/100km)	30 (7.8 l/100 km)	31 (7.6 l/100 km)	+3.3%
Highway mpg (l/100 km)	42 (5.6 l/100 km)	46 (5.1 l/100 km)	+9.5%
Combined mpg (l/100km)	34 (6.9 l/100 km)	36 (6.5 l/100 km)	+5.9%

The engine block is cast iron, with a forged steel crankshaft that runs in five main bearings and has four counterweights. In order to counteract engine vibration and maintain smooth operation, the EA288’s crankshaft is connected to two gear-driven counter-rotating balance shafts that spin at twice engine speed.

Friction has been reduced by about 15% throughout through the use of roller bearings for the drivetrain side camshaft, increased piston-to-wall clearance, and lower piston-ring tension, among other measures.

Novel valve layout and VVT. The aluminum-alloy cross-flow cylinder head has a novel placement of intake and exhaust valves; the intake and exhaust ports for each cylinder are positioned one behind the other in the direction of flow. Because of the arrangement of the intake and exhaust ports, each overhead camshaft operates one intake valve and one exhaust valve per cylinder (as opposed to one camshaft for intake valves only and one for exhaust), allowing for greater air delivery and swirl. In other words, there is not a separate intake or exhaust camshaft.

Top: Valve layout. Bottom: VVT operating mode and valve timing with the new valve layout.Click to enlarge.

Normally on an engine, you have the intake valve on one camshaft and you have the exhaust valve on the other camshaft. What we did here, we rotated the valve stem by 90 degrees. This means we have on the one camshaft one intake valve and one exhaust valve. And on one of the camshafts we combined this with a cam phaser. This gives us the opportunity to run a kind of a Miller cycle on a diesel engine, because at low rpm, low load, you are only utilizing one intake valve. We can now adjust about 50 ˚ crank angle.

—Oliver Schmidt, General Manager, Engineering and Environmental Office, Volkswagen Group of America

The camshafts are driven by the crankshaft by a toothed belt and the camshaft gear of one of the camshafts. The two camshafts are joined by a spur gear. The camshafts are integrated into a separated housing by a thermal joining process, helping ensure a very rigid camshaft bearing while keeping the weight low.

To reduce friction, a needle bearing is used for the first bearing that receives the highest forces from the toothed belt drive. A sensor wheel is located on one camshaft; the signal from the sensor tells the ECM the current position of the camshafts.

The cylinder head features a two-section coolant jacket, as well as a three-part cooling circuit and switchable coolant pump. The lower coolant jacket core has a larger volume, to provide a high level of heat dissipation in the part of the cylinder head close to the combustion chamber. The flow of coolant from the upper and lower parts merge at the spur gear side of the cylinder head where it exits through a combined outlet.

Fuel system. Volkswagen raised the fuel injection pressure on the base engine from 1600 to 2000 bar. Schmidt noted that in Germany, pressures in the engine are as high as 2500.

Volkswagen worked with Bosch to modify the injector for the system, which now contains a mini-rail—a small chamber with pressurized diesel so there will always be 2000 bar available.

The injector with with solenoid valve technology can perform several injections per work cycle. In the past only injectors with piezo actuators were able to meet these performance demands.

Emissions. The 2015 TDI Clean Diesel is the first Jetta to have a Selective Catalytic Reduction (SCR) catalytic converter and complex exhaust gas recirculation system. This layout enables extremely fast response by the oxidation catalytic converter and the SCR catalytic converter. This helps reduce the oxides of nitrogen (NO_x) using the AdBlue additive. Compared to the NO_x storage catalytic converter (NSC) of the previous model, the use of the SCR catalytic converter helps reduce emissions and improve fuel economy.

Top. The close-coupled exhaust aftertreatment system already enables LEV III compliance. Bottom. Characteristics of the integrated DPF/SCR unit. Click to enlarge.

The EA288 engine has the intercooler for its turbocharger system integrated directly into the intake manifold, which serves a two-fold purpose of increasing throttle response and performance as well as helping lower emissions.

The diesel particulate filter, with optimized porosity, has high washcoat amounts of a thermally stable SCR coating. The design results in low exhaust back pressure and high filtration efficiency. Mixture preparation is in the in transfer tunnel, and uniform NH₃ distribution avoids urea deposits .

The exhaust gas aftertreatment module is mounted very close to the engine, helping to lower heat and pressure losses. Volkswagen improved the pressure losses in the low pressure EGR system by some 90%, bringing it down from 200 to 20-25 millibars.

Overall, Volkswagen was able to reduce raw NO_x emissions out of the engine by some 40%; with the use of the scaleable emissions treatment possible through the modular exhaust gas aftertreatment components through the MDB, Volkswagen is currently able to meet emissions standards up to EU 6.2 and LEV III/Tier 3.

Like the Jetta GLI, the Jetta TDI sends its power to the wheels through either a standard six-speed manual gearbox or an available DSG dual-clutch automatic transmission.

Chassis and Suspension. All Jetta models are fitted with a strut-type front suspension with coil springs, telescopic dampers, and an anti-roll bar. They also have a multilink independent arrangement that features three transverse and one longitudinal link per wheel. This enables the longitudinal and transverse dynamics to be precisely configured almost independently of each other. The result is more agile, responsive and precise handling. All Jetta models have an anti-roll bar as part of the rear suspension.

2015 Jetta TDI. Click to enlarge.

Exterior. The sixth-generation Jetta (introduced in 2011) was bigger, with a longer wheelbase and 2.9 inches added to the overall length, than its predecessor. For 2015, Volkswagen further refined the design. The 2015 model brings a redesigned radiator grille with three cross fins, a new bumper, and optional Bi-Xenon headlights with Adaptive Front-lighting System (AFS). Each daytime running light is formed by 15 LEDs arranged in an L-shaped string alongside and beneath the xenon modules.

This new look is further accentuated by a chrome element between the LED daytime running lights and the xenon lights. The visual band formed by the radiator grille and headlight clusters, as well as the larger lower air intake, give the Jetta a wider and more substantial appearance. This new look is finished off with optional foglights mounted in the outer areas of the bumper.

These lighting elements are available as part of a new Lighting Package, which is available on the Sport, 1.8T SE with Connectivity and Navigation, 1.8T SEL and TDI SEL trims for $995. It includes interior ambient lighting, the Bi-Xenon headlights with dynamic cornering and LED daytime running lights, and an upgraded display in the instrument cluster.

Aerodynamics. Aerodynamic improvements affect fuel economy. The new bumper and air intakes up front help to reduce air drag, as do updated rain gutters near the A-pillars. The underside of the Jetta now features paneling at the rear axle that, along with the sill covers with wheel spoilers and modified brake ventilation channels (1.8T only), help maintain a smooth flow of air along the car.

On Jetta 1.8T and 2.0 TDI Clean Diesel models, the radiator grille features a closeable shutter, a feature which assists in improving aerodynamics (by guiding frontal airflow around the body) and fuel efficiency, as well as offering greater thermal control of the engine.

By keeping the shutter closed during warm-up, the engine can reach operating temperature faster, after which the shutter is automatically opened and closed as needed.

The 2015 Jetta features an updated rear design, including a new trunk lid, taillights, emblems, and bumper. The new trunk lid features an aerodynamic trailing edge—an integrated spoiler that lines up with the car’s silhouette near the character line, extending smoothly into the rear fenders.

2015 Jetta TDI (manual transmission). Click to enlarge.

Interior. A benefit of the Jetta’s extended wheelbase (104.4") is a spacious interior, with rear-seat legroom of 38.1 inches. The gently arcing roofline provides headroom of 37.1 inches for rear-seat passengers.

The Jetta offers a class-leading 15.5 cubic feet of usable trunk space, which can be increased by folding forward the 60/40-split rear seatback. The rear seatback is also offered with a pass-through to help accommodate longer items, such as skis.

The new Jetta offers several optional features based on trim: a new multifunction steering wheel; redesigned air vent controls; interior piano black and chrome accents; ambient lighting; and new seating fabrics. Standard equipment and options packages have been updated and reconfigured throughout the model line-up, and now include a selection of new driver assistance systems not available on 2014 Jetta models. (Volkswagen has yet to add USB ports, however.)

Entry-level Jetta models come well equipped. The Jetta 2.0L S has standard air conditioning, Bluetooth connectivity, a multifunction steering wheel, cruise control, one-touch auto up/down power windows, power locks with keyless entry, aux-in for the radio/CD player, and power heated exterior mirrors.

Premium features that are offered on Jetta’s various trims include: a six-way power driver’s seat; a leather-wrapped multifunction steering wheel; dual-zone automatic climate control; a sunroof; a soft-touch dashboard; two-tone V-Tex leatherette sport seating surfaces; RNS 315 navigation system; Fender Premium Audio System (400 watts of power through nine speakers and a trunk- mounted subwoofer); Keyless access with push-button start; Volkswagen Car-Net connected services; and a rearview camera.

Safety. The 2015 Jetta comes on sale with a Top Safety Pick+ award (the highest award) from the Insurance Institute for Highway Safety, after a structural upgrade to improve small overlap protection and the addition of an optional front crash prevention system. (Earlier post.)

Safety in the 2015 Jetta starts with a stiff and rigid bodyshell constructed using seamless laser welding and high-strength steel in key areas. Also standard on all Jetta models are driver and front passenger front and side thorax airbags and Side Curtain Protection airbags front and rear. There is also a standard suite of advanced electronic safety features, such as Anti-lock Braking (ABS), Electronic Brake-pressure Distribution (EBD), Electronic Stability Control (ESC), and Hydraulic Brake Assist (HBA).

Driver Assistance. For 2015, a number of new driver assistance systems are offered on the Jetta, including Blind Spot Monitor plus Rear Traffic Alert and Forward Collision Warning. Also available are the new Bi-Xenon headlights with LED daytime running lights and the Adaptive Front-lighting System (AFS), in which the headlights track the Jetta’s steering angle and can turn up to 15 degrees in response, helping to better illuminate corners in turns.

The available new Blind Spot Monitor system utilizes a flashing symbol in the outer area of the side mirrors to help indicate the presence of vehicles in the blind spot next to the Jetta. The system uses radar sensors to help monitor a space around the vehicle with a range of approximately 65 feet. Jetta models that are equipped with Blind Spot Monitor are automatically equipped with the Rear Traffic Alert system as well.

The Blind Spot Monitor system utilizes a flashing symbol in the outer area or the side mirrors. Click to enlarge.

This new available Rear Traffic Alert system not only helps alert the driver to stationary and moving vehicles directly behind the Jetta, but also helps detect vehicles approaching from the side that may be difficult for the driver to see. Like the Blind Spot Monitor, it offers a range of 65 feet (20 meters), and will present an acoustic warning and apply the brakes if a potential impending collision is detected.

Similarly, the Forward Collision Warning system uses radar sensors to help monitor the distance of traffic ahead of the vehicle. Hidden behind the Volkswagen logo on the radiator grille, the radar sensor acquires both the position of stationary cars and motorcycles as well as those moving in the same direction as the Jetta.

Within physical system limits, Forward Collision Warning helps warn the driver of critical front-end collision situations, both acoustically and visually by a clear warning symbol in the instrument cluster.

These systems are either standard or optional depending on trim. Blind Spot Monitor with Rear Cross Traffic Alert and Forward Collision Warning are available in the Driver Assistance Package, which can be had on SE with Connectivity and Navigation and 1.8T SEL trims, while the TDI SEL trim offers them in the Driver Assistance and Lighting Package, which combines them with the Lighting Package equipment.

Driving. The Jetta TDI is fun, smooth, relatively quiet and quite efficient to drive in both manual and DSG configurations. In our opinion, the enhanced power, handling, refinement and further improved fuel economy allow the Jetta TDI to maintain its competitive lead over the Chevy Cruze diesel, itself a fine car.

In a combustion-engined car, especially one that encourages some spirited driving (as opposed to a more leviathan-style cruising), we strongly prefer a diesel/manual transmission combination. Here, Jetta does not disappoint at all. The new EA288 is wonderfully responsive, and the six-speed manual delivers smooth shifting.

One of our subjective niggles with the Cruze diesel was the responsiveness of the Aisin-Warner six-speed automatic under certain conditions—e.g., kickdown from stop or from very slow speed. We ended up adopting a hybrid shifting strategy for those conditions: manual select mode to step rapidly up through the lowest gears, then over to automatic.

The 2015 Jeta TDI with DSG forced no such compromise. The automatic is quick and responsive, and worthy of the splendid new EA288 engine.

Subjectively (as controlled measurement is somewhat difficult under the conditions of the quick drives), the Jetta TDI appears to err on the conservative side for its fuel economy numbers. In other words, we seemed to be able to deliver better-than-rated fuel economy under the different driving routes; while the 2015 Jetta TDI has a EPA combined rating of 36 mpg, we found ourselves looking at returns along the line of 42 mpg by drives’ ends. (And clearly, road driving conditions were quite different than the EPA test cycles, but these were far from highway-optimized routes where diesels shine.)

In terms of noise, the Jetta TDI, like the Cruze diesel, is pleasingly quiet, with the distinctive diesel sound almost undetectable in the cabin. From the outside, however, both are clearly diesels.

At idle, the TDI is louder in cabin that its 1.8-liter gasoline counterpart: 48 dB vs. 42 dB, with no air conditioning, etc. On the road at 45 mph, however, that difference disappears: both the Jetta TDI and the 1.8L gasoline engine came in at 60 dB. (dB measurements made with SPLnFFT on iPhone 5s. Open access paper from the Acoustical Society of America on smartphone sound measurement applications available here.)

(Now if Volkswagen would just add a couple of USB ports…)

2015 Jetta TDI trim levels
Trim	Contents
2.0L TDI S	The 2.0L TDI S is the entry model for the clean diesel range, with a starting MSRP of $21,640. It offers the new 2.0-liter EA288 TDI Clean Diesel engine; six-speed manual transmission; electromechanical speed-sensitive power steering; 16-inch steel wheels; chrome grille; heatable front seats; cruise control; Media Device Interface (MDI) with iPhone adapter; SiriusXM Satellite Radio. A six-speed DSG automatic transmission will add $1,100 to the MSRP.
2.0L TDI SE with Connectivity	The SE with Connectivity (starting MSRP of $24,075) adds body-color exterior mirrors with turn signal indicators; chrome window trim, and power heated side mirrors. Inside, it offers V-Tex leatherette seating surfaces; driver seat lumbar adjustment; rear seat armrest with passthrough; soft-touch dash; leather-wrapped multifunction steering wheels and handbrake; sunroof; VW Car-Net® connected car features; Premium VIII touchscreen radio; rearview camera; and Keyless entry with push-button start. A six-speed DSG automatic transmission adds $1,100 to the MSRP.
2.0L TDI SEL	With an MSRP starting at $26,410, the SEL builds on the 2.0L TDI SE with Connectivity and adds: six-way power driver seat; Fender Premium Audio System; Homelink; keyless entry with push-button start; dual-zone automatic climate control; RNS 315 navigation system; rearview camera; foglights; and “Lancaster” 17-inch alloy wheels. The Driver Assistance and Lighting Package is available, and includes interior ambient lighting; Forward Collision Warning; Blind Spot Monitor with rear cross traffic alert; Bi-Xenon headlights with dynamic cornering and LED daytime running lights; and an upgraded display in the instrument cluster. Outfitting the car with a six-speed DSG automatic transmission will bring the MSRP to $27,510.