The 2015 Golf TDI is one of the diesels VW has temporarily stopped selling in the US.

For motorists looking for sporty but environmentally friendly alternatives to sluggish hybrids, diesels like the Volkswagen Jetta TDI has been a welcome addition to the U.S. market. The ability to deliver real performance along with high mileage is one reason why diesel sales have continued to grow even as demand for gas-electric models has plunged in the face of cheap gas.

But that growth spurt is likely to sputter out, industry insiders warn, in the wake of the Volkswagen cheating scandal. Last week, the Environmental Protection Agency ordered the recall of 482,000 VW diesel models, revealing that the maker had used software to scam the government’s emissions tests.

In real world situations, vehicles like the Jetta TDI actually produce up to 40 times the permissible level of noxious emissions.

“This is another black eye for diesels,” said Mike Jackson, CEO of Florida-based AutoNation, the country’s largest automotive retailer. “You now have a passionate constituency that feels betrayed.”

(CEO’s resignation just latest twist in VW scandal. Click Here for the latest.)

If the VW mess isn’t enough, a new report from Germany indicates the government has found that at least one diesel model sold there significantly exceeds European Union emissions standards – which are generally more lax on diesels than in the U.S. Government officials are now calling for random roadside checks to avoid the possibility other automakers secretly developed software to game the testing process.

The Range Rover Sport TD6 could face a perilous challenge winning over buyers now.

In the late 1970s and early ‘80s, in the wake of twin Mideast oil shocks, high-mileage diesels experienced explosive growth. But the “oil burners” of that era were generally slow, noisy and foul-smelling. A variety of other problems caused the market to collapse here, especially as emissions standards were ramped up. By 2007, light-duty diesel sales – excluding a handful of heavy-duty pickups – fell to just 16,700.

In Europe, however, demand was soaring as a new generation of supposedly “clean diesels” was introduced. The technologies that helped make them more environmentally friendly – such as turbocharging – also boosted performance. In some cases, these new models also delivered highway mileage equal to comparable hybrids. By the beginning of this decade, roughly half of the vehicles sold in Europe were diesel-powered.

Though American and Asian makers were reluctant to return to the market here, German brands rushed over an assortment of diesel models. And sales started to take off, growing to 57,800 by 2009, and last year hitting 163,200, according to estimates from AutoPacific, Inc.

Until this week, the consulting firm was one of many to project even bigger growth as more manufacturers began to add new diesels. Fiat Chrysler scored a hit with the Ram 1500 diesel pickup, Chevrolet recently added a version of its Cruze sedan. Jaguar Land Rover is launching an array of diesel models, including the 2016 Range Rover TD6.

(Click Here for a review of the 2016 Range Rover Sport Td6.)

But such plans could be put in jeopardy by the VW brouhaha, warned AutoPacific’s Ed Kim. “The potential impact puts years of effort and millions of dollars of investments to waste,” he said.

With Volkswagen ordering at least a temporary hold on U.S. sales of its four-cylinder diesel models – which last year accounted for a quarter of its demand here – the numbers will take an immediate plunge, Kim said. But he doesn’t forecast much of a rebound, at least not initially.

Sales of heavy-duty trucks, like this Ford Super Duty are less likely to be impacted by the VW scandal.

AutoNation’s Jackson agreed, fearing potential buyers who wanted something efficient yet sporty will now be more reluctant to trust any manufacturer’s clean diesel claims.

During a Wednesday web conference, officials from the Washington-based Technology Forum attempted to put a more positive spin on the crisis, a statement from the trade group arguing that, “The circumstances involving a single manufacturer do not define an entire technology, or an industry. Vehicle manufacturers and engine makers have invested billions of dollars in research and development to successfully meet the most aggressive emissions standards in the world.”

But whether American motorists really will differentiate between brands is far from certain. And the situation would likely get only worse for diesel makers and proponents if BMW – or any other manufacturer – also proves to be missing those emissions standards.

Adding further downward pressure, petroleum prices are continuing to slide even as automakers introduce new gas-powered models that are getting better and better mileage, also without much sacrifice in performance.

Add it all up, said analyst Kim, “and this is going to push diesels back quite a few years.”

(Diesel still likely to be the engine of choice for 2017 Ford Super Duty. Click Here to check out the new pickup.)

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