The four-door Unlimited model was the biggest change to Jeep's iconic Wrangler in years. But the next generation of the Wrangler may need to be very different to survive, Fiat's CEO says. Source: Fiat Chrysler.

Jeep fans, take note: Fiat Chrysler (NASDAQOTH: FIATY) CEO Sergio Marchionne is threatening to mess with your icon. 

Marchionne said this week that the next-generation Jeep Wrangler may need to undergo radical changes in order to survive. It may be based on a carlike unibody platform, have a small turbocharged engine, and have aluminum body panels instead of the current steel.

And it may not be built in Toledo, where Wranglers have been built for decades. 

Would such a vehicle even be worthy of the Wrangler name?

The iconic Wrangler is the Jeep brand
The Jeep Wrangler is, of course, the heart and soul of the Jeep brand, something that Fiat Chrysler executives acknowledged when they laid out their plans for Jeep earlier this year.

But in recent years, the Jeep brand has evolved. Other Jeeps now have "soft-road" versions, versions that aren't quite capable of the off-road feats that have defined the Jeep brand for decades. 

That has helped draw a lot of new customers to the brand. Softer Jeep SUVs can be more comfortable to drive on normal roads than the serious off-roaders that Jeep has long built. Of course, Jeep has made sure to offer a "Trail Rated" version of each new Jeep, one that carries on the brand's tradition of serious off-road prowess.

It's working: Jeep sales are up a whopping 45% this year, thanks in big part to the success of the unibody Cherokee.

New unibody Jeeps like the Cherokee have shown that they can be capable off-roaders. Source: Fiat Chrysler.

Jeep enthusiasts have grudgingly accepted this compromise -- partly because the "Trail Rated" Jeeps have turned out to be pretty good, but also because there's still one Jeep that hasn't gone soft: The Wrangler. 

The Wrangler is still built with traditional body-on-frame construction that provides the right stiffness and clearance for its extremely capable suspension. It's still built with rugged steel body panels and torquey, naturally aspirated engines -- and it's still built in the Toledo, Ohio factory that has turned out Wranglers for many years.

For all of the changes that have come to the Jeep brand, the Wrangler is still the Wrangler -- at least for now. Source: Fiat Chrysler.

All of that is extremely important to Jeep enthusiasts. In many eyes, the purity of the Wrangler is what makes Jeep "Jeep."

But what Marchionne said this week is that all of that might be about to change.

Why even the Wrangler may have to evolve to survive
Here's the problem: The next Wrangler has to get better fuel economy than the current model. 

Current Wranglers are powered by Chrysler's "Pentastar" 3.6 liter V6. It's a good engine with plenty of power: 285 horsepower and 260 lb-ft of torque. But even the smaller of the two Wrangler models, the two-door version, only gets 17 miles per gallon in the city and 21 on the highway. (The bigger four-door Wrangler Unlimited is rated at 16 city/21 highway.) 

Part of the problem is weight: A two-door Wrangler weighs almost 3,800 pounds. The Wrangler Unlimited is about 300 pounds heavier. Wranglers aren't huge vehicles, but all of that sturdy steel adds up. 

Reducing the Wrangler's weight would allow Fiat Chrysler to fit a smaller engine. Done right, that would improve fuel economy without sacrificing performance. A turbocharged engine could add additional improvement: Simply put, modern turbos allow a small engine to give big-engine power when you need it, while using less gas in normal day-to-day cruising.

One way to reduce the Wrangler's weight without reducing its size would be to build much of it out of aluminum. Another would be to shift from its current body-on-frame construction to a lighter "unibody" platform -- to build it like a car rather than like a truck, in other words. 

But building such a Wrangler would require hundreds of millions of dollars' worth of changes to the Wrangler's current factory in Toledo, and those changes may not be in cash-strapped Fiat Chrysler's budget. It's likely that an aluminum unibody Wrangler would be built in one of Fiat Chrysler's other North American factories, Marchionne said.

Now, none of this means that the Wrangler will be ruined. Jeep has shown with its other models that it can still get Jeep-like off-road performance with unibody construction. 

But it will definitely be different, even if it doesn't look much different on the outside. Will Jeep fans buy it?

There's a precedent for these kinds of changes
These are probably the same questions that Ford (F 0.08%) executives were asking as they began the redesign of the Blue Oval's own iconic product, the F-150 pickup.

As you've probably heard by now, the 2015 F-150 will have body panels made of aluminum instead of steel. It'll be offered with a smaller engine, Ford's 2.7 liter "EcoBoost" turbo V6 -- though more powerful options will be available. And the weight savings are significant: It'll be as much as 700 pounds lighter in some versions than the outgoing truck.

Ford has spent months reassuring its customers that the new aluminum F-150 is a properly tough and brawny Ford truck. That careful groundwork looks set to pay off. Source: Ford Motor Company.

Ford's leaders felt like this was something they had to do. Corporate average fuel economy regulations are going to get a lot tougher over the next few years. Ford CEO Mark Fields has said that the new F-150 will actually help Ford's corporate average fuel economy ratings, rather than holding them back as past versions have.

But there's no getting away from it: These are radical changes for America's top-selling vehicle, and they're very risky ones: This is Ford's most profitable and important product. It won't be on sale for a couple of months yet, so we don't know for sure how buyers will react. But Ford executives are very confident that it'll do well.

How a radical Wrangler could succeed
Of course, Ford has spent months laying the groundwork for its new truck in the market, talking in detail about the harsh field-testing it went through and its many improvements.

Ford's track record suggests that the new truck will probably be very good, and it'll probably sell very well. 

It's certainly possible for Fiat Chrysler to build a lighter, more efficient Wrangler that will also be very good and sell well -- and that will be accepted as a Wrangler, just as the new F-150 is  being accepted as a proper new Ford pickup. 

But the company will have to go to great lengths to sell it to its wary enthusiasts, just as Ford has with its new F-150.

Will they? We'll find out.