Most new diesel cars still pollute beyond legal limits

Tests by consumer organisation Which? have found that a large number of new diesel cars still exceed the new, tougher emissions limits in “real-world” testing.

Much fanfare has been made about the new WLTP and RDE fuel economy and emissions tests that were introduced by the EU last year, and which will apply to all new cars from this September. But based on the Which? research, a number of car manufacturers are still exploiting weaknesses in the testing procedures to build cars that pump far more toxins into the air than they should.

The tests have found that although some petrol cars produce excessive emissions when put through more rigorous testing than the EU requires, it is new diesel cars that are still spewing the highest levels of pollution from their exhausts.

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Confirming what we already knew

Based on the outgoing NEDC emissions limits, Which? found that a whopping 77% of new diesel cars tested in the last 18 months exceeded the legal emissions limits when put through more rigorous testing. In reality, this is hardly news anymore – we’ve known since before the Volkswagen Dieselgate scandal broke that manufacturers had been gaming the emissions regulations for years.

The official government fuel economy numbers were a joke, and therefore emissions were as well, because the official NEDC tests simply weren’t tough enough (and yet Volkswagen still couldn’t build engines that could pass these basic tests without cheating…).

But all this was supposed to come to an end with the new, tougher WLTP laws. It was claimed that manufacturers wouldn’t be able to outwit the new tests, so the results would be truly representative of what buyers could expect when they bought a new car. Every new model released since September 2017 has had to comply with the new rules, and by September 2018 (just two weeks away as this is written) all new cars on sale must comply. So, good news all round, right?

Diesel cars still poisoning our air

Sadly, no. Which? claims that more than half of the new diesel cars they have tested in recent months still pump out far more pollution than the new rules allow, because those new rules still don’t properly represent real-world driving in sensible real-world conditions.

The test protocols used by Which? are stricter than the EU’s new scheme, yet they are hardly unrealistic. For example:

• Cars are tested in the default setting they start up in, rather than switching them to an ‘eco mode’ as the EU allows manufacturers to do for official tests.
• All test cycles are conducted with the air conditioning, headlights and radio switched on.
• In addition to running the EU’s new WLTP test, Which? also conducts a proper motorway cycle, which official tests do not have.
• Cars are tested with a 200kg payload, which is roughly equivalent to two adults, a bit of luggage and a tank of fuel.
• The tests are lab-based, but if the results seem suspicious, the car is driven on real roads and emissions are measured using a PEMS (portable emission measuring system).

Which? has tested 61 new diesel models using these protocols since the start of 2017. 47 of those 61 cars (77%) failed to meet the outgoing NEDC emissions requirements. 33 out of the 61 cars (54%) failed to meet the new WLTP emissions standards.

So how can these offending cars be allowed on sale?

The government tests are softer than the Which? tests, so manufacturers still have wiggle room to ‘optimise’ their vehicles for best possible results. And, obviously, they do everything they can to get the best results – even though they know the results will not be realistic.

They can switch the car into an eco mode (that most drivers never use because it makes the car sluggish and unresponsive to drive). They are allowed to turn off air-conditioners, radios, headlights and anything else that may use fuel. They don’t have to account for passengers, luggage or any fuel in the tank beyond what’s needed to complete the test. They can pump up the tyres way past a comfortable or safe level to reduce rolling resistance. Plus various other tricks and ploys.

All of these little loopholes add up to big differences in the final results, but the level of variation reported by Which? is astonishing. We’ve republished their full table below. The worst offender – the Subaru Forester – was found to be producing 25 times the legal emissions levels, yet still passed the old NEDC tests.

How does your car rate?

Here is the list of cars tested by Which? and their results. We’ve added columns to show how they rate against the old (NEDC) and new (WLTP) tests.

The new legal emissions limit from now until 2020 is actually double the current standard, as a sop to manufacturers from the EU for making the tests tougher. From 2020, the levels will decrease by 40%, although that still makes them 50% higher than the old NEDC levels.

As you can see, the Subaru Forester is the worst of all, exceeding the current limits by more than 2400% (in other words, it produces about 25 times the legal limit) and exceeds the new limits by 1100% (about 12 times the new limit). It also produced more than double the emissions of the second-worst car, the Renault Grand Scenic. Renault also has five cars in the ten worst offenders.

At the other end of the scale, the BMW 2 Series Active Tourer and Mercedes-Benz E Class are model citizens. Which? was so surprised by the big Mercedes’ outstanding score that it put the E-Class through the RDE road test protocol to check it against the lab figures, but the results were very similar so it is definitely a genuine score.

What does this all prove?

Well, firstly it’s important to state that all of the cars above passed their official government lab tests – even the Subaru and all those Renaults – so there is no question that they are legal. What is shows is how inadequate the regulations are at properly cracking down on emissions levels from diesel cars.

Industry bodies like the SMMT can bleat on about how efficient and environmentally-friendly modern diesel engines are, but the above tests show that it’s largely a charade. So don’t be surprised when governments and councils continue to levy additional taxes on diesel cars, and don’t believe industry representatives who complain that it’s not fair.