Missed Signals and the Overheating Taxi

Dear Car Talk

Dear Car Talk | Mar 26, 2013

Dear Tom and Ray:

I drive a taxicab in Austin, Texas, and I'm feeling flummoxed! The 2008 Chrysler 300C that I drove blew its head gasket. Here's where I get confused. The temp-gauge needle stayed approximately in the middle, and there was no Hot Engine warning light and bell. When I started my shift, I noticed that the car was a little hard to start. But it got going with no noises and ran smoothly, so I thought, "No problem." I went to the airport and proceeded to wait a couple of hours for a fare. It was humid, so I idled with the AC going. I smelled coolant, so I checked on the ground to see if I had a leak. All I saw was water. It seemed like condensation, so again I thought, "Hmm, no problem." I pulled into the loading area. I loaded my fare in to the car and started off.

Here's where it gets interesting. The Check Engine light came on. Performance was a little squirrely for a bit, and then I noticed white smoke coming out of the tailpipe. I mistakenly thought it was because the fuel mixture wasn't right, causing the white smoke. The engine continued to run smoothly, though, and after a couple of miles the smoke stopped. But the warning light remained on. We cruised down the highway for about 10 miles before coming to a red light. As I came to a stop, the engine died, and when I tried to restart, black smoke came from the engine compartment.

I called a tow truck. When the mechanic checked out the car, he saw that a coolant hose that feeds into the coolant reservoir had a small hole in it. I guess this would explain the coolant smell from earlier. But why didn't the engine register as overheating? Wouldn't this be natural when a head gasket fails? This is where I become flummoxed! Tell me, please, what should I have done, if anything, to avoid this catastrophe?

-- Russ "The Cabbie"

RAY: If it makes you feel better, Russ, we can tell you there's not much you could have done to prevent this.

TOM: If that doesn't make you feel better, then we'll tell you the truth ... which is that you said, "Hm, no problem" when the better response would have been, "Hm, problem?"

RAY: You lay out a complicated series of events here, so anything we say will be pure speculation about what happened. But that's never stopped us before.

TOM: My guess would be that your head gasket was already leaking that day, but not enough for you to really notice it. It wouldn't leak coolant onto the ground; it would leak into one of your cylinders and get vaporized and sent out the tailpipe.

RAY: That could be the coolant you were smelling. Then, for any number of reasons -- the heat, the stress, the age of the car, the position of Aquarius in the southern sky -- your head gasket picked that day to get much worse. As it let more coolant seep into a cylinder, you finally noticed white smoke, which was the vaporized coolant, coming out of the tailpipe.

TOM: You never lost enough coolant to overheat the engine that day, but you lost enough to eventually stop it from seeping into the cylinder, which stopped the coolant vapor, or white smoke.

RAY: Then, my guess is that something completely unrelated made the car stall. My first guess would be that your alternator failed.

TOM: That could explain why the car was hard to start in the morning (the battery wasn't charging properly), why the car finally stalled and wouldn't restart (the battery and alternator both were dead) and why there was a brief billowing of black smoke (the alternator seized and caused its belt to heat up and smoke).

RAY: And then, upon examination, your mechanic discovered the blown head gasket.

TOM: What could you have done? Well, maybe nothing. But there were several red flags along the way that should have gotten you to at least scratch your head, if not pull over immediately.

RAY: The reddest of those red flags is when all the idiot lights on the dashboard lit up, the car's performance got squirrelly and you saw voluminous plumes of white smoke coming out of your car.

TOM: Those were hints that something was wrong, Russ.

RAY: And since you ignored all of those hints, your final hint was one you couldn't ignore: the car dying at an intersection with a paying passenger in the back seat.

TOM: For future reference, if you ever have any signs of overheating, it's important to pull over and stop driving the car. If you keep driving, you easily can turn a simple cooling-system problem into a blown head gasket, or turn a blown head gasket into a cracked head.

RAY: Pulling over and shutting off the car when you suspect it's overheating is good advice, Russ. Don't be afraid to stop next time. A cracked head or cracked block will cost you many times more than one lost fare.

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