Saturday, 23 August 2008

Hybrid vs diesel fuel consumption comparison

Quite a lot of fuel consumption comparisons among hybrid and diesel cars have already been or are run these days so here comes mine. This one, however, isn’t based on single test cases performed by automotive editors in specific atmospheric, road and vehicle wear and tear and driving habits conditions but on “real life” fuel consumption observed over a long time and published by cars owners on an excellent monitoring web page Spritmonitor.


1. It’s almost certain that a plug-in hybrid system is the way to go in terms of oil independence for (at least) automotive applications. Please see the comments for further information.

2. In compact and midsize cars, a hybrid drivetrain in its current setup provides same sort of fuel consumption advantage over a diesel-powered car as diesel-powered cars can provide over their state-of-the-art petrol counterparts. This applies to cars with very similar performance. Toyota Prius II uses roughly a liter of fuel less than most frugal VW Golf and Passat 1.9 TDI achieve when averaged (due to the Prius falling somewhere between those two cars in terms of size). The same liter of fuel more over average consumption of these diesels is needed to cover about 60 miles (~100 km) with a VW Golf TSI 120 HP. It’s worth noting however that some fraction of mileage advantage Prius offers is related to its very aerodynamic water-drop shape, low-grip tires and continuously variable transmission (CVT), none of the features VWs possess.

3. In midsize SUV category, the situation is far more surprising. While the Lexus RX 400h hybrid fares better than most diesels which either consume essentially more while not being able to match the hybrid performance or consume much more when performing equally good (this applies to V8 diesels with very heavy drivetrain components to withstand extremely high torque), BMW offers diesels which excel the hybrid easily. This does not only show in case of lighter and smaller X3, but also in case of full-size X5 with twin-turbo 3-litre diesel engine which is even quicker than the RX 400h and consumes less as well. Because technically most advanced competitors were present in the comparison, it turns out that BMW became the best diesel manufacturer in terms of performance and fuel economy in the world as for now. It’s also likely that, after the appearance of twin-turbocharged diesel cars from other manufacturers, non plug-in hybrid drivetrain in its current form may no longer be the benchmark of mileage in automotive industry.

See it for yourself

Compact and mid-size cars.


Mid-size SUVs.


Comments to this research

This comparison considers raw fuel consumption only, not the cost-saving and environmental factors (partly due to complexity of such analyses and prices of petrol and diesel fuel getting nearly equal at the time of writing).

Beside hybrids currently in production and widely available, a modified versions of Toyota Prius and Ford Escape Hybrid (which uses same Hybrid Synergy Drive technology) offered by Oemtek company [1] were confronted with all the rest. These aftermarket modifications install an additional battery pack, rendering the car a plug-in hybrid since it can be charged at home using a standard socket and then cover about 30 miles (about 50 km) running on electricity only. The manufacturer claims extremely impressive fuel consumption figures. This however, in my opinion can be achieved only when travelling short distances. That’s the only situation when the car can cover say a half of the distance without using its internal combustion engine. Still, since I believe most of drivers don’t travel more than 60 miles (~100 km) per day, a plug-in hybrid appears to be the way to go if the goal is to slash dependence on oil. Further reasons for a plug-in hybrid drivetrain to succeed are its long range (on petrol) if needed and already available charging infrastructure (electricity net), a statement false for any hydrogen-powered vehicle. Energy needed to power a plug-in hybrid car can be produced from sources (like nuclear, hydroelectric and coal power plants or natural gas) which are far less likely to deplete as quick as crude oil will probably do [2].

Since Toyota Prius is not easy to classify, it was compared with both VW Golf (which in its 4-door version is a bit longer than Prius but has much shorter wheelbase) and VW Passat (same wheelbase as Prius but overall longer). Two VWs have been picked as these are most popular cars [3][4] in its class in Europe. EuroNCAP classifies Prius as a large family car [5] which competes with Passat rather than Golf.

Following versions or makes of vehicles were compared: Toyota Prius II, VW Golf mkV, VW Passat B6, first makes of Lexus RX 400h, VW Touareg, Audi Q7 and Volvo XC90, second makes of Mercedes ML and BMW X5s as stated on the charts.

After realizing how well modern BMW diesels perform against hybrids in SUV territory, fuel consumption of BMW 118d (the 105 kW version of the engine, after first remake) was checked if it can beat selected contenders but with average consumption of 6,17 l/100 km (38,2 MPG or 45,8 imp-MPG) it was decided it can’t provide any new significant perspective to this comparison.

BMW X3 3.0d was picked despite its general classification as a compact crossover SUV [6] while the Lexus RX 400h is considered a midsize crossover SUV [7] as it has very similar wheelbase to the hybrid SUV tested.

Volkswagen 1.4 TSI engines were added to the comparison as, in my opinion, these are currently the best petrol powerplants on the market due to their low cubic capacity, presence of forced induction (turbocharger in the low output version and, additionally a supercharger in the more powerful one) and very desirable driving characteristics, with relatively much power in the low revs band (high torque). Presence of TSI engines was considered a good example of how much fuel consumption advantage can a modern diesel and hybrid setup provide over a modern petrol engine.

Audi Q7 is included in this comparison only for a SUV representing VW AG TDI technology in application other than relatively heavy duty off-roading (like in VW Touareg, a SUV much heavier than most of its competition) to be present in the comparison. Meanwhile, one needs to realize Q7 is not a mid-size SUV but a full-size one.

[3] Most popular compact cars in Europe in 2007
[4] Most popular midsize cars in Europe in 2007
[5]EuroNCAP Toyota Prius classification

Spritmonitor fuel consumption sources and 0-62 mph (0-100 kph) acceleration sources:

Fuel consumption data:

Toyota Prius II
VW Golf 2.0 TDI
VW Passat 2.0 TDI
VW Golf 1.9 TDI
VW Passat 1.9 TDI 105
VW Golf TSI 120 HP
VW Golf TSI 140 HP
Lexus RX 400h
VW Touareg 2.5 TDI
VW Touareg 3.0 TDI
VW Touareg V10 TDI
Mercedes ML 320 CDI
BMW X5 3.0d E53
BMW X5 3.0d E70
BMW X5 E70 3.0sd
Mercedes ML 420 CDI
BMW X3 3.0d
Volvo XC90 d5
Audi Q7 3.0 TDI

Acceleration data:

AMiS 2005/11 for Volvo XC90 d5, Mercedes ML 320 CDI, VW Touareg 3.0 TDI, BMW X5 3.0d E53.
Passat 2.0 TDI
Golf 2.0 TDI
Golf 1.9 TDI
Passat 1.9 TDI 105 HP
BMW X5 3.0sd
Golf TSI
Touareg V10 TDi Mercedes ML 420 CDi
Lexus RX 400h
Toyota Prius II

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