Dear Car Talk:

Our daughter was driving her 2005 BMW X5 in town at around 20 mph when it suddenly stopped. She pulled over to the side of the road and tried to start it, with no luck (it acted like it had a dead battery, and would not do anything). It was towed to a BMW dealer, and the dealer said that the engine had seized. There were no warning lights on when the car died, nor did anything on the dashboard indicate that something was wrong -- even after the car died when we turned the ignition switch to "run." Just the usual lights. What happened, and was there anything that could have prevented the catastrophe? Thanks.

-- Don
 
Well, Don, there are several possibilities here, depending on why the engine seized.

The most common reason engines seize is that they run out of oil, or lose oil pressure. If that's what happened to your daughter's X5, one possibility is that the oil light was flashing, the orange "warning" triangle was lit up, the chime was ding-dinging, the lifters were clacking like mad and your daughter just didn't notice any of that. Or she's too embarrassed to tell you she ignored it all so she could get home in time to watch "Game of Thrones."

Whether that's a realistic possibility is something you'd know better than I would, Don. You're her father. So you know both her fibbing propensity and her obliviousness-while-driving quotient.

There aren't many people who would not notice that kind of three-alarm cacophony. Although there are people who would keep driving to "try to get home" rather than pull over and shut off the car right away (which is the proper, engine-saving response).

So a more plausible scenario is that the timing chain broke. In that case, there would have been no dashboard warnings.

A timing chain is supposed to last the life of a vehicle, within reason. But if it breaks, the pistons will come up at the wrong time and crush a bunch of the valves, leaving the crankshaft unable to turn. That would lock up the engine, just as if you had run out of oil and melted the crankshaft to the bearings.

Could your timing chain disaster have been prevented? Probably, yes. But not by looking for lights on the dashboard.

When a timing chain gets loose -- which is its first step in breaking -- it'll start to make noise. A lot of noise. That's something her regular mechanic probably would have noticed. If she has a regular mechanic. And if she took her car to him regularly.

So if she had taken the car to a good mechanic every 5,000 or 7,500 miles for oil changes and regular maintenance, she might have been presented with a $1,500 bill for a timing chain replacement (a bummer) rather than a $10,000 bill for a remanufactured engine (a catastrophe).

And, in general, that's a primary reason we recommend regular service to our customers -- not just so we can afford HBO. Sorry for your loss, Don.