ST. GEORGE, Utah — Jeep has been on this quest for decades — “the Holy Grail,” said Jim Morrison, the marque’s boss since June — for a diesel engine suitable for the Wrangler.

“Since I’ve been in this job, the three things Jeep customers keep telling me they want are a pickup truck, a diesel in a Wrangler and the return of the Wagoneer,” Mr. Morrison said last month at a media event in Utah. “We delivered on the truck with the introduction of the Gladiator. Here, we’re unveiling the first Wrangler EcoDiesel. No comment on the Wagoneer.”

He added: “The customers were right. This version of the Wrangler has the perfect mix of driving dynamics, four-by-four capability, fuel economy and torque.”

In a way, it has made little sense that the Wrangler never had a diesel option in its decades of existence. Gasoline engines are suited for speed — which the boxy, high-riding Wrangler itself is not. Gas engines get inherently worse fuel economy.