Dear Tom and Ray:

Yesterday a vehicle crashed into some trees near my house. The driver apparently had passed out while driving and was not conscious, but his foot was still on the gas. The engine was racing and the tires were spinning, and there was a lot of smoke. My son was able to reach through the passenger side and turn off the engine. I was afraid it was going to blow up. Which leads to my question: How long would it take for a racing engine to blow up? Or would it "blow up" from racing like that?

-- Judy

RAY: The engine would not blow up, Judy. Just to be sure, I went outside and drove my brother's car into a tree to try it, and I can confirm that, unlike the front grille, the engine is still completely intact.

TOM: In the old days, you could make an engine "blow." What was meant by that was that you could rev the engine so fast that centrifugal force would cause important engine parts to start flying apart.

RAY: But you can't even do that anymore. All modern cars have rev limiters, which cut the fuel supply to the engine before the engine speed reaches the danger zone.

TOM: The smoke you saw likely was coming from one of two places: Either the radiator was fractured when the car hit the tree and what you were seeing was lots of steam, or the tires may have been smoking.

RAY: And while we commend your son for helping the gentleman, and we'd certainly try to do the same thing, there are three types of dangers in a situation like this, for future reference.

TOM: One is that the car breaks loose from the tree or whatever is holding it in place. If it's a small tree, or if he hit it with the corner of the car, and the wheels are really spinning, the car could free itself and take you with it while you're leaning into the passenger window.

RAY: The second danger could come from the tires. If the tires are spinning quickly on the ground, they'll be creating tremendous friction. And if they get hot enough, they could catch fire.

TOM: Or, if a tire ends up spinning while it's off the ground, the speed of the spinning tire could cause the tire to fly apart and potentially hurt somebody.

RAY: And the third danger is that the guy who passed out could wake up and say: "Hey! Who the heck are you, and what are you doing in my car?"