THE Australian motoring media has long lamented the lack of a diesel engine option in the huge and hugely opulent Lexus LX four-wheel-drive. And now the brand has finally listened, transplanting the 4.5-litre twin-turbo diesel V8 from the Toyota LandCruiser 200 on which the big Lexus is based. 8650 less than the V8 petrol-powered LX570. After a week living with the derv-devouring LX, we remained unconvinced that the diesel transition was particularly successful or worthwhile. No two ways about it, the Lexus LX450d is bloody expensive. 134,500 plus on-road costs. 14,170 more than the LandCruiser 200 Sahara diesel on which it鈥檚 based. It costs about the same as a Mercedes-Benz GLS350d Sport or Range Rover Sport HSE SDV6. 23,600 more than the Infiniti QX80. 23,600 difference in fuel savings. But none of the above rivals can hold a candle to the Lexus鈥?LandCruiser breeding - although the Infiniti does have Nissan Patrol guts - and we鈥檇 wager the Lexus holds its value better than the Europeans and the Infiniti.

134,500 in a Lexus LX450d? But it鈥檚 what the LX450d doesn鈥檛 have compared with the petrol LX570 that gets interesting. For a start, it loses the third seating row, so it can only carry five rather than eight people. Also gone are 44 litres of fuel tank capacity, meaning the diesel鈥檚 extra efficiency has little impact on range. You can鈥檛 drown out the diesel drone with the petrol version鈥檚 19-speaker Mark Levinson premium audio system or entertain rear passengers with the LX570鈥檚 seat-mounted dual 11.6-inch screens. The LX450d also misses out on a sunroof and the six-speed automatic transmission has two fewer ratios than the eight-speeder in the petrol version. 17,490 Enhancement Pack that upgrades a petrol LX570 with 21-inch alloys, front seat ventilation and heating/ventilation for the outer second-row seats. But you do get the same Lexus-exclusive interior, and it鈥檚 a pleasant place to spend time. We happened to step into the LX after spending a week with the Infiniti QX80 and it was like travelling 10 years forward in time. Overall, the ambience is of hi-tech opulence. It looks and feels great.

The big 12.3-inch multimedia screen looks state-of-the-art, as does a similarly large head-up display readout projected onto the windscreen. The adaptive cruise control could be better in operation, frequently being more annoying than relaxing as the LX ran away with itself down hills or surged and braked as traffic changed lanes in front of us. Otherwise, the cabin layout is pretty straightforward and clutter-free for an environment with so many different functions on offer. Lexus has gone for a decent balance of buttons and screen-based operation rather than cramming everything into the multimedia unit at the expense of usability. We鈥檇 rather rotary climate controls than the push-button variety, though, and keep those rear climate controls hidden away in the fold-away rear armrest if you have curious toddlers onboard. As you鈥檇 expect, cabin storage is pretty comprehensive throughout and the chilled centre console compartment that can take four large drinks bottles is an inspired inclusion for road trips.

By contrast, the fold-and-tumble mechanism of the rear seats and the split tailgate operation are pretty agricultural and reveal this car鈥檚 LandCruiser origins. On that note, our ivory-upholstered example had clearly been used for some remote-area off-roading and some of the light-coloured surfaces seemed to be terminally stained and prematurely aged as a result. Not exactly practical, then. It鈥檚 just as well, because forward visibility over that precipitous bonnet is not great, even with the driver鈥檚 seat cranked right up. Side and rear visibility is OK considering the sheer height of the car, but even a normally conspicuous Tesla Model S managed to completely vanish into a blind spot during our week with the Lexus. Lexus has done its best to mute and muffle the big diesel V8 but on start-up, idle and on the move, there is no escaping its rattly burble and vibration under acceleration. 140k luxury apartment on wheels was closely related to, and sounded like, that of a 70 Series farm truck.

For comparison, the 5.7-litre naturally aspirated V8 engine in an LX570 develops 270kW at 5600rpm and 530Nm at 3200rpm, with an eight-speed automatic transmission and 14.4L/100km on the official combined cycle. It鈥檚 really hard to imagine this vehicle really being used out bush, so its lumbering and lethargic on-road character courtesy of this engine choice makes it a real chore. And that鈥檚 on top of the un-Lexus levels of noise and vibration already mentioned before. But we took it on some muddy forest tracks anyway, which is where it all made much more sense. The effortless, utterly controllable and predictable low-speed grunt is everything you want on tough terrain. The transmission shifts are spot on, selecting low-range is simple and everything just works. It鈥檚 just baffling that the tank range advantage this diesel engine would logically bring is squandered by a reduction in onboard fuel capacity. But for slow, difficult off-road work it probably would be much more efficient than the petrol and less likely to be troubled by water crossings. But who exactly is going to take this thing up the Gibb River Road?