Dear Car Talk:

When starting my Camry cold, white smoke billows from the rear tailpipe. What is this? -- Sherry



This is the universal signal to grab a new auto-loan application, Sherry.

Well, maybe not. But white smoke usually is caused by vaporized coolant, which often is the result of a blown head gasket.

At the middle of the engine, you have the cylinders, which combust gasoline and air. All around those cylinders are passages for coolant, to keep the cylinders from overheating. And when everything is correct, the twain never shall meet: Coolant stays outside the cylinders, and the combustion materials stay inside.

But when there's a breach -- like a blown head gasket -- the coolant, which is under high pressure, will seep into one or more of the cylinders after you turn off the engine. Then, when you restart the engine, that coolant gets combusted, along with the gasoline and air. And that makes white smoke.

So, the first thing to do is ask your mechanic to do a head-gasket test. If he believes the head gasket is bad, then you'll have to decide whether to put $1,000-plus into the car.

That'll depend on how old the car is, what kind of shape it's in, whether you still love it, and how much credit is available on your home-equity line.

Of course, once he opens up the engine, he might find that it's worse than a blown head gasket: that it's a cracked head, or a cracked block -- which both are way more expensive. So be aware that there's some uncertainty going into any such operation.

And depending how close the call is regarding whether to fix the car or dump it, you may want to issue a DNR in case the mechanic discovers a crack in the head or block. I'll think good thoughts for you, Sherry