IT IS unusual to test a new vehicle that’s being hailed as a big deal that has had exactly zero exterior changes and almost no interior changes. The 150 Series Prado has been in service since 2009, and received a pretty big makeover in 2013, so Toyota hasn’t seen it necessary to tweak it further.

“This vehicle still researches incredibly well,” said Toyota Australia executive director sales and marketing Tony Cramb. “It’s a great-looking, tough 4WD that a traditional four-wheel driver loves the look of.

“We did make some changes just a couple of years ago and they were fairly extensive exterior changes. The opportunity this time was engine, fuel efficiency and those kinds of things. There have been a couple of small specification changes, but the vehicle is selling very well, and we’re satisfied with it.”The biggest change, of course, has come under the bonnet, with the fitment of Toyota’s new diesel engine, the 1GD-FVT. The level of technology that has been poured into this engine family is impressive – but necessary, given how widely it will be spread across the Toyota family.

While Prado is the first to carry it, the 1GD (or Global Diesel) will end up in both the HiLux and the Fortuner, both of which we will see in Australia soon.

In 1GD form, it’s a single-turbo four-cylinder diesel of 2.8 litres capacity, with an output of 130kW and 450Nm when coupled with Toyota’s new six-speed automatic, which also makes its debut in the Prado.

The numbers aren’t significantly different from the 1KD – up just three kilowatts and 40Nm – but one big change is fuel efficiency, where it drops from 8.5 to 8.0 litres per 100 kilometres in auto guise (the manual is 7.9L/100km).

Another big change comes in the area of noise, vibration and harshness (NVH) reduction. The Prado’s old 3.0-litre diesel felt like… well, a 15-year-old diesel engine. While it was tractable and capable, it was quite noisy and harsh, especially when pushed.

The new Euro 5-rated motor sports several key improvements over the outgoing engine, including replacing the timing belt with a longer-lasting, quieter timing chain, a lightweight resin valve cover, roller-rocker valve gear and a water-cooled exhaust gas recirculation system.

Toyota’s engineers have also reprofiled the pistons, reinforced the turbo mounting point and engine mounts, and added extra insulation to the oil pan to reduce the engine’s noise.

The six-speed automatic, too, is new and quite clever, with a couple of key modes to aid progress. A so-called high-speed gear-effective utilisation mode, for example, assesses whether the car needs fifth or sixth gears, based on the incline and road speeds.

A deceleration downshift control mode also maximises the fuel-cut sequence, combining with the throttle that now also has an instant open/closed mode.

What does all this tech mean in the real world? The new 1GD engine gives the Prado a new lease on life. It’s quiet at idle and at cruise, is muted under all but the heaviest of right feet and wafts the Prado along with real composure.

Highway and country road cruising is now a quiet and relaxed affair, with more wind noise from the big external mirrors in evidence than diesel grumble, even up to 110km/h.

The Prado’s soft suspension tune just adds to the character of refinement, with even the worst of undulations and broken tarmac gobbled up by the supple wheel travel.

The new automatic gearbox quickly defaults to its tallest gears, but can be manipulated via a Sports mode or overcome completely by the sequential shift lever.

Over 150km of testing, we saw fuel figures of 8.5 litres per 100 kilometres.

Off-road, the engine is hugely tractable and flexible, making short work of even the steepest pinches. Though we really didn’t understand the science, Toyota has managed to minimise throttle flutter in steep and undulating terrain by smoothing out the inputs to the engine, even if the driver’s foot is being jerked around on rough ground.

All is not perfect, though the Prado is a weighty SUV – in base GX trim, it weighs 2205kg, pushing out to over 2400kg in top-spec Kakadu – and on steep, long road climbs, the new engine combo can be found wanting, especially when looking for a little more zip to make a pass or blend with traffic.

One gets the feeling that the 1GD’s being stretched almost to the edge of its performance envelope with the big Prado, and that it will perform better in the smaller, lighter HiLux/Fortuner models.

This is borne out by the towing capacities of the respective cars – the Prado is limited to 2500kg, while the forthcoming HiLux will use the same engine and gearbox to lug around up to 3500kg.

Despite the uphill shortfall – and despite minor price rises across the line-up, the new diesel engine for the Prado is a big step forward in refinement and comfort, while providing better fuel economy and lower emissions. The Prado will still be a top seller for Toyota for some time to come.