Dear Tom and Ray:

Love your show and your column! I'm sure you have seen the Viagra commercial on TV in which the intrepid driver notices that his muscle car is overheating. He swings jauntily into a service station, buys a cold bottle of water and immediately pours its contents into his radiator, then drives merrily on his way. Now, I'm just an old schoolmarm, so maybe my information is out of date, and if so, you can set me straight. But I was always told: (1) Never even try to take the radiator cap off of a hot radiator. It could blow scalding steam in your face. (2) Never put water in an overheated engine, as you could crack the block. (3) When you do add water, you should start the motor before you pour anything into the radiator so that it circulates. If I'm right, and the guy in the advertisement is wrong, then ED is the least of his problems. Please comment!

-- Chrissy

RAY: You're right, Chrissy. On most cars, if he popped off the radiator cap while the car was overheating, he'd have second-degree burns all over his face and arms. And no amount of Viagra is going help him if he looks like he just got worked over with a bag of chisels.

TOM: In general, you never, ever should remove a radiator cap while an engine is hot. Especially if the car is overheating. You want to give it a good 45 minutes to an hour to cool down, and then, still, open it very slowly and carefully, using a large rag for hand and arm protection.

RAY: Unless you have a car with a separate, unpressurized coolant-recovery bottle. Then you can remove that cap right away. The 1969 Camaro used in that ad may have been one of the last cars to have one of those. So you're right, Chrissy, but this particular car is an exception to the rule.

TOM: Normally -- like you say -- you would wait until the engine cools off before removing the cap. So you wouldn't add any fluid to the radiator when the engine is red hot, either. Adding cold water to an overheated engine can potentially damage the block.

RAY: But with an unpressurized recovery bottle, you can add fluid anytime, because it doesn't go directly into the radiator. It sits in the recovery bottle and gets sucked into the cooling system later, when the engine cools down.

TOM: On most cars, you would want to wait until the engine cooled off before adding cold water. In fact, that's why old-timers suggest you run the engine -- so the cold water circulates and mixes with the hot water immediately.

RAY: But in reality, once the engine is cool enough that you can safely remove the radiator cap, you can pour in cold water without fear of damaging the block. So, at that point, running the engine while adding fluid is unnecessary. Although some purists will argue that it's best to run the engine anyway, to avoid trapping any air in the system.

TOM: But here's where Romeo went wrong: Adding a 1-pint bottle of Fiji water is unlikely to solve his problem. It's not enough water to make a difference if he's really overheating, and more importantly, it doesn't solve the problem that led to the overheating in the first place (probably a leak, a stuck thermostat or a plugged radiator).

RAY: So if the commercial continued for another three minutes, he'd be overheating again. Not as much as he'll be overheating from all that Viagra, but overheating nonetheless.