Sector: Lower medium Price: £22,335 Fuel: 72.4mpg CO2: 104g/km

Vauxhall has been subtly but effectively updating its core models for over a year now, and the Astra is the latest to get a small but important upgrade for its fleet presence, in the form of a new Euro 6 compliant 1.6-litre diesel engine.

Though the two are being sold alongside each other at the moment, the 1.6 CDTi is the unit which will replace GM’s long-running, hard-wearing 1.7-litre diesel family. So this single engine, which is already available in the Zafira Tourer and Meriva, and likely to be headed for the Insignia in the near future, stands to be a staple of Vauxhall’s future fleet presence.

It’s a thoroughly modern unit, too. Vauxhall has used a variable turbocharger to offer smooth and progressive power delivery, a new multiple injection common rail system for a more efficient combustion cycle and fitted a NOx trap in the exhaust to meet Euro 6 requirements. The six-speed gearbox is also new.

Like its predecessor, the 1.6 CDTi is available in two power outputs – with 108bhp and 134bhp – and headline fuel economy figures have improved with it. Likely to be the fleet engine of choice, the 108bhp version emits 97g/km CO2 and returns 76.3mpg, down from 74.3mpg and 99g/km for the equivalent 1.7 CDTi.

Unfortunately, this wasn’t available to test. Instead, we spent some time with the 134bhp unit, which in its most efficient form returns 72.4mpg and emits 104g/km CO2. That’s actually slightly higher than the nearest equivalent 1.7 CDTi, at 74.3mpg and 99g/km, though Vauxhall has hinted at further improvements in the near future.

Bringing CO2 under 95g/km for one or both of them would certainly be helpful from a BiK and capital allowance point of view. Especially PSA’s Euro 6 compliant BlueHDI 120 offering more power (118bhp) and CO2 emissions from 82g/km in the Astra-rivalling Peugeot 308. Even the larger Insignia isn’t far off the Astra, with 2.0 CDTi versions now down to 98g/km.

However, there’s a lot to be impressed with here. GM calls this the ‘Whisper Diesel’ and, even from cold, the engine lives up to its nickname. There’s a barely perceptible whirr, but almost no rattle even when idling and the engine is almost silent while driving. It’s a huge change from the 1.7 CDTi, which was hardly a noisy engine, but was starting to fall behind others on the refinement front.

Power delivery is strong and, even in the more powerful version, it lacks a mid-range spike which some downsized engines can suffer from. While the claimed economy isn’t the best in this class, Vauxhall has form for coming close to its published figures in real-world use and a 1.6-litre engine is neither overpowered nor overwhelmed in a car of this size, which should help. 

It’s also worth remembering that this generation of Astra is close to retirement. Spy shots have already shown its replacement being tested under heavy camouflage, rumoured to launch during 2015. So while improvements to fuel economy are minor in this car, expect the Whisper Diesel to have fuel economy to really shout about when it makes its way under the bonnet of the next Astra.

Verdict:

The 1.6 CDTi is a delight to drive in the Astra, with impressive refinement and on-road performance. However, this is a fiercely competitive sector and running costs are still behind several of its key rivals – a factor Vauxhall needs to address quickly.