RAY: Roger Meyer sent this puzzler in to us. I always attribute the puzzler. There are no innocents here at Car Talk.

Here it is:

A group of explorers were trapped in Alaska for the winter season. Stuck in the ice and snow, they only had one means of escaping to civilization before spring. They had in their possession an old World War Two airplane with skis, which they could use in the event of an emergency.

The plane had a placard on the instrument panel that said, in bold red letters, "Do not attempt to start engine with oil temperature below minus forty degrees Fahrenheit."

Did I mention it was cold?

Well, wouldn't you know it, but a medical emergency arose, and when the pilot checked the oil temperature gauge, he discovered it was broken. As luck would have it, this being an international kind of team, all of their instruments were in Centigrade.

Unfortunately, nobody could remember the formula for converting Centigrade to Fahrenheit. Skip, who had been carefully looking over the engine for the last couple of days, emerges from—are you ready for this?—the inky shadows of the dimly lit Quonset hut.

The others ask, "Do you know the formula for converting Centigrade to Fahrenheit?"

He says, "I don't need no stinkin' formulas. But, I know you can start the engine. It will be all right."

They say, "Okie dokie!" And, sure enough they start the engine up, and it's fine. Of course, the propeller fell off-- but that's another story.

The question is, how did Skip know they could safely start the airplane's engine?