What Happened When I Accidentally Filled Up A Diesel Cadillac Escalade With Gasoline

Photo: Cadillac

During our first pit stop near Hagerstown, Maryland, I jumped out of the 2023 Cadillac Escalade I was reviewing, dunked my credit card in the pump, and filled the tank — two-thirds empty after about 350 miles. highway driving – with premium unleaded.

I had missed all the signs. The faint redline, the cranky torque, the 25 mpg fuel economy, even the warning message on the fuel-filler door. Turns out the Escalade I was borrowing for a week-long vacation with my boyfriend’s family was powered by GM’s 277-hp, 460-lb-ft 3.0-liter turbodiesel inline-six . The existence of a diesel Caddy in the 2023 model year – especially after the ignominy suffered by the brand with its appalling diesel dabbling in the 70s and 80s – was beyond me.

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I fully accept blame for my mistake, but I was driving the truck under the influence – of SuperCruise, the world’s best hands-free highway driving system. During our freeway ride, it dazzled me on several occasions, able to speed up, slow down, steer, stay on course and detect obstacles, all without the help of my big mitts. Even more fun, when another motorist inhibited our set speed, the Caddy would automatically find an opening, change lanes, overtake and return to the right lane, a skill that 90% of human motorists lack. I was thrilled, which rarely happens when driving a barn-sized SUV.

Amazingly, my daydream continued for another 250 SuperCrusing miles after my accidental gas-up. In fact, it wasn’t until we were within walking distance of our AirBnB, on a winding lane plunging into West Virginia’s Greenbrier River Valley, that the first hints of a problem arose. Big Slade began to shiver; as we pulled into the driveway, it collapsed in a dramatic miasma of soot.

Photo: Cadillac

Photo: Cadillac

A look in the trunk while unloading our bags confirmed my worst guesses: 600 D – for Diesel, or Duramax, or in my case, Dumb. I was so ashamed that I didn’t tell my boyfriend until the tow truck was on the way.

Everything I had read about this stupid error suggested that simply starting the engine with the wrong fuel would render it permanently inoperable. So how did I manage to drive the equivalent of Detroit to Chicago without realizing it?

“It’s a bit of a compliment to me and our team for this engine, to say it didn’t even look like a diesel,” John Barta, deputy chief engineer of GM’s Duramax small engines, told me over the phone. . “But while he box running on gasoline is not the right fuel mix for this,” he said. “And then all these other bad things happen.”

These “bad things” happen in an increasingly negative cascade. In the best case, you realize the error before starting the engine. “Now your problem is just inside the tank,” Barta said. “If you can stop there, it’s a lot easier to manage. Have it towed to a dealer. They can empty the tank and put fresh diesel in it, and you’ll be good to go.

If you start the vehicle, the low pressure fuel pump in the tank feeds fuel to a high pressure pump in the engine compartment capable of 36,000 psi. Very soon after, gasoline and diesel are completely mixed; bad fuel is everywhere. It’s corrosive. “The diesel actually lubricates the pump,” Barta said. “Gasoline is basically a solvent. So when you remove that lube and then wash it off, you end up with a significant amount of wear in that pump. After just a few miles in that condition, it’s necessary to drain and flush the entire fuel system.

The greater the exposure to gasoline, the greater the wear becomes. Eventually, metal shavings from unlubricated pumps enter the fuel and travel through the system. Filters in each fuel injector help somewhat, but if the particles are fine enough, they can pass through the nozzle and interrupt fuel flow, causing what Barta called “terrible injection events.”

After that, things get really ugly. A diesel engine burns its fuel without a spark plug, under intense pressure. Gas fouls this equation, causing late burning. This generates a huge amount of soot. This soot then enters the diesel particulate filter in the exhaust system. Typically, when a DPF fills up, the engine computer briefly injects more fuel, which automatically burns the DPF. But gasoline does not have the necessary energy content for good ignition here. “Eventually you create so much soot, it clogs the filter, and then you basically have a blockage so the exhaust has nowhere to go,” Barta said. “Probably, that’s why your engine eventually stalled.”

Fixing this properly requires all of the above fixes, plus replacing low and high pressure fuel pumps, injectors and fuel lines. Not a cheap procedure.

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

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

It all makes sense. Yet I wondered how this cataclysm had never arisen for hours on the road with the wrong fuel flowing into the tank. In the end, our steady-state SuperCruising must have helped. “Our engine is quite fuel efficient,” Barta said. “So if you were just working at low load – if you burn less fuel, you’ll get less soot.”

At gas stations, diesel fuel nozzles are larger in diameter than gasoline nozzles, to prevent customers from inadvertently filling a gasoline car with diesel, but you can easily slip a larger gasoline nozzle small in filling a diesel. This protection is a bit counter-intuitive, as it is much less damaging to refuel a petrol car with diesel than the other way around. “Diesel fuel, although it doesn’t allow the gasoline car to run well at all, at least is not corrosive to the system,” Barta said. A simple fuel system flush will fix a gas powered car without worrying about long term damage or durability. Perhaps in response to my recent confusion, Barta added, “We would never recommend that you put the wrong fuel in your engine, and our warranty coverage does not cover those accidents.”

GM doesn’t really track the incidence of this kind of idiocy among its customers, but Barta noted that errors like mine are not unheard of. “I mean, does that happen? Yes, it happens. I don’t have a rate on how often that happens,” he said. “But I think it happens in all of our diesel products. It’s like having a car accident. It’s an accident. Nobody plans to do that.

While the folks I spoke with at GM wanted the flatbed SUV at a Caddy dealership, the closest was 130 miles away. Luckily there was a Chevy shop just ten minutes away that had handled this fix several times. The Caddy was due back in New York at the end of the week, so the Chevy dealer simply drained and flushed the entire fuel system and refilled the tank with good diesel – a $750 bill, but way less than what I expected. (Despite my protests, GM’s fleet management company, FMI, graciously footed the bill.) Then the service manager tested it for 300 miles, to make sure it ran smoothly.

I risked a catastrophic failure by driving the Caddy north. But in 600 miles it didn’t even stutter and felt as solid as before my filling accident. Overall fuel economy for our 1,500-mile trip, despite running on gasoline, was 26 mpg.

It’s not a mistake I see myself making again. However, given our continued shift to electrification, there’s always the chance I’ll try pumping unleaded into a Celestiq.

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