What happened when a diesel accidentally filled a Cadillac Escalade with gasoline

Photo: Cadillac

At our first pitstop near Hagerstown, Maryland, I got out of the 2023 Cadillac Escalade I was reviewing, dipped my credit card in the pump, and filled the tank—two-thirds depleted after about 350 miles of highway driving—with premium unleaded.

I missed all the signs. Low redline, tight torque, 25 mpg fuel economy, even a warning message on the fuel filler door. As it turns out, the Escalade I borrowed for a weeklong vacation with my boyfriend’s family was powered by GM’s 277-hp, 460-lb-ft 3.0-liter turbodiesel flat-six. The existence of a diesel Caddy for the 2023 model year — especially after the embarrassment the brand faced with diesel engines in the ’70s and ’80s — was beyond me.

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I take full responsibility for my mistakes, but I was driving under the influence of the truck – SuperCruise, the world’s premier hands-free highway cruise control system standard. On our highway track, it dazzled me time and time again, managing to accelerate, decelerate, steer, stay on course and detect obstacles without the benefit of my big gloves. Even more amusingly, when another motorist interrupted our speed limit, the Caddy would automatically find an opening, change lanes, pass and return to the right lane, a skill that 90 percent of human drivers lack. I was impressed, which rarely happens behind the wheel of a warehouse-sized SUV.

Amazingly, my dream lasted another 250 SuperCrusing miles after an accidental gas fill-up. In fact, it wasn’t until we were within walking distance of our AirBnB, on a winding lane into West Virginia’s Greenbrier River Valley, that the first signs of trouble occurred. Great Slade began to tremble; As we pulled into the driveway, the soot conked out in a dramatic miasma.

Photo: Cadillac

Photo: Cadillac

A glance at his trunk as we unloaded our bags confirmed my worst guess: 600 D — for Diesel or Duramax, or in my case Dumb. I was so embarrassed that I didn’t go to my boyfriend until the tow truck left.

Everything I read about this stupid bug indicated that starting the engine with the wrong fuel would permanently disable it. So how did I manage to drive the Detroit equivalent to Chicago without noticing?

“It’s kind of a compliment to me and our team to say that it doesn’t even look like a diesel for this engine,” John Barta, GM’s assistant chief engineer for the smaller Duramax engines, told me over the phone. “But this time be able if you run on gasoline, it’s the wrong fuel mixture for it,” he said. “And then all these other bad things happen.”

These “bad things” happen in an increasingly negative cascade. Best case scenario, you realize the error before starting the engine. “Now your problem is inside the tank,” Barta said. “If you can hang in there, it’s a lot easier to deal with. Take it to a dealer. They can empty the tank and put in fresh diesel, and you’re good to go.”

When you start the car, a low-pressure fuel pump in the tank delivers fuel to a high-pressure pump in the engine compartment at 36,000 psi. Before long, gasoline and diesel are completely mixed; the wrong fuel is everywhere. It’s abrasive. “Diesel actually oils the pump,” Barta said. “Gasoline is basically a solvent. So when you remove that lube and then wash it, you end up with a significant amount of wear on that pump. In this case, after only a few miles, the entire fuel system needs to be drained and flushed.

The longer you are exposed to gasoline, the more severe the wear. Eventually, metal shavings from unlubricated pumps get into the fuel and circulate through the system. Filters on each fuel injector help somewhat, but if the particles are fine enough, they can get into the nozzle and stop the fuel flow, causing what Barta calls “horrible injection incidents.”

After that, things get really ugly. A diesel engine burns fuel under high pressure without a spark plug. Gas disrupts this equation and causes delayed combustion. This creates a large amount of soot. This soot then enters the diesel particulate filter in the exhaust system. Typically, when a DPF fills up, the engine computer injects more fuel for a short period of time, which automatically cleans the DPF. But gasoline does not have the energy for proper ignition here. “Eventually, you build up so much soot, it clogs the filter and then you’re basically clogged, the exhaust gas has nowhere to go,” Barta said. “That’s probably why your engine stopped at the end.”

Correctly repairing this requires all of the above adjustments as well as replacing the low and high pressure fuel pumps, injectors and fuel lines. Not a cheap procedure.

The Escalade's 3.0L Duramax diesel is so smooth and quiet that I took it to be a gasser in the worst possible way.

The Escalade’s 3.0L Duramax diesel is so smooth and quiet that I took it to be a gasser in the worst possible way.

It all makes sense. Still, I’m surprised this cataclysm didn’t rear its head while burning in a tank of fuel on the road for hours. Apparently, our steady state SuperCruising should help. “Our engine is pretty fuel-efficient,” Barta said. “So if you’re just running low-load—burning less fuel—you’re going to get less soot.”

Diesel fuel nozzles at gas stations have a larger diameter than gasoline, which prevents customers from mistakenly filling a gas car with diesel, but you can easily slide a smaller gasoline nozzle into a diesel filler. This protection is somewhat counterintuitive, since filling up a gas-powered vehicle with diesel is, on the contrary, less harmful. “Diesel doesn’t make a gasoline car run as well, but at least it’s not corrosive to the system,” Barta said. A simple fuel system flush will fix a gas-powered vehicle without worrying about long-term damage or durability. Perhaps in response to my latest confusion, Barta added, “We never recommend putting the wrong fuel in your engine, and our warranty does not cover these accidents.”

GM doesn’t really track this kind of stupidity among its customers, but Barta noted that mistakes like mine aren’t unheard of. “I mean, does that happen? Yes, it does. I don’t have a rate on how often that happens,” he said. “But I think that’s the case with all of our diesel products. It’s like being in a car accident. This is an accident. No one plans to do that.”

The people I spoke to at GM wanted the SUV flatbed at a Caddy dealer, but the closest one was 130 miles away. Fortunately, there was a Chevy shop just ten minutes away that had handled this fix many times. The Caddy had to return to New York at the end of the week, so the Chevy dealer simply drained and cleaned the entire fuel system and filled the tank with good diesel – a $750 bill, but much less than I expected. (GM’s fleet management company, FMI, graciously paid, despite my protests.) Then the service manager gave it a 300-mile test drive to make sure it was running properly.

I risked a catastrophic failure driving the Caddy north. But at 600 miles it didn’t even stutter and felt as rock solid as it did before the charging mishap. Overall fuel economy for our 1,500-mile trip was 26 mpg, even with gasoline.

It’s not a mistake I’m making myself again. Although, given that we’re continuing to go electrified, I’m going to try hitting the Celestiq unleaded.

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