Last month I marveled at the comfort of my fiancée’s . It was old-school American luxury mixed with the kind of delightful hubris that led General Motors to believe that it would pull buyers from Mercedes and BMW. But that car, with its La-Z-Boy levels of comfort is now dead after hydrolocking on a bright and sunny day. Here’s why.

The heart of the Oldsmobile LSS was GM’s Buick 3800 V6, an engine known for being practically bulletproof. The 3800 is one of those engines that you’d think will survive the end of the world, outliving mankind itself. But there is an easy way to kill one, and it’s making it drown in its own coolant.

Last Wednesday, I hopped into the LSS to drive myself to the airport for a press event. We’d had the car serviced by a mechanic only a few days before. The LSS now had new tires, spark plugs, wires, PCV valve, belts, EGR, throttle body and a coolant flush. It got an alignment and new bearings, too, which eliminated a lot of the sloppy handling that I described in my post.

The LSS felt faster, too. I accelerated onto the highway toward O’Hare International Airport and settled into an 80 mph cruise, setting my sights on getting there just in time to slide through security.

It wasn’t long into the trip before the car began requiring a bit more throttle input to maintain speed. I couldn’t put my finger on why, but the reason would reveal itself as soon as we hit Chicago traffic. We came to a dead stop and the 3800 made a loud metallic noise.

The noise was louder than the rod knocks that I’m used to hearing, but not quite something like a lifter tick, either. The engine was also idling like crap and the temperature gauge began a march towards the red. I hoped for something simple like a destroyed serpentine belt slapping about the engine bay but before I could pull over the engine shut off and would not restart.

With the help of an awesomely helpful trucker we got the car onto a shoulder. It was the wrong one, but we weren’t blocking traffic anymore.

The belt was still there and the engine leaked no fluids. The only thing that looked bad was the coolant reservoir, which spilled over the top with coolant that smelled like it was tainted with oil.

Particles were also in the coolant that weren’t there before.

Unsure what’d happened, I tried starting it and the starter couldn’t turn the engine over. Huh.

We called in a tow truck and I tried to revive the Oldsmobile while we waited for rescue to arrive. As the engine cooled, the starter was once again able to turn the motor, but it would never turn over fast enough to start the car.

Amusingly, we faced another, really stupid problem.

The tow company said that we could not ride in the truck, so we had to book an Uber. This would be fine if we were able to find an Uber driver willing to pick someone up from a highway shoulder. Instead, drivers told us to ride in the tow truck or to run across four lanes of busy traffic. Sure, I’ll get right to playing real life Frogger.

One driver gave up after he overshot us and pulled over. The tow truck to also overshot us then attempt to tow the Uber. This was supposed to be a super serious situation, but I couldn’t help but laugh.

The car was towed to a new mechanic, who gave us a saddening diagnosis: The engine hydrolocked after four cylinders filled themselves to the brim with coolant.

Those four rods were bent with plenty of cylinder scoring and so much coolant got where it didn’t belong that the engine block itself cracked. As you’d expect, those four cylinders make basically zero compression. The engine will start after you clear the coolant out of the cylinders, but it’ll run on two cylinders just long enough for the other four to clog up with coolant again.

According to the mechanic, the engine most-likely overheated due to a massive air bubble in the cooling system. They also discovered that the plastic intake manifold on top of the engine, which has coolant flowing through it, was cracked and leaking. Intake manifold failures are a pretty common sight and there are even aftermarket versions available made out of far sturdier materials. It’s unknown whether that crack happened before or during the engine’s meltdown.

Either way, the engine is toast, with a rebuild costing more than the entire car is worth. The Oldsmobile is parked outside for now. And its future is uncertain. She wants to save it, but it might be easier to cut her losses and move on.

One thing’s for sure, even a supposedly bulletproof engine can be killed if you have a bad enough day.