Q:I have a question for you and would like your opinion on the topic, too. I have asked a few friends and am getting a variety of answers. This is on a 1936 Chevy street rod project. Do I need to put a sort of shroud on the sides of the radiator? The reason I'm asking is that I was thinking that air (like water) finds the area of least resistance. If I don't block off the sides of the radiator, will this reduce the effectiveness of the radiator? I have a great dual 11-inch puller fan and shroud set up for the back of the radiator but was thinking that maybe I need to fabricate a shroud for the sides of the radiator. - Jerome B., Andover

A:Let's look at how the radiator works and proceed from there. A car radiator takes hot water, which in large volume holds its heat well, and spreads it out thin over a wide surface area. The water's heat is transferred to the metal and then dissipated by moving air.

When the radiator sits in still summer air, it heats up quickly so that little heat transfer can take place. Hot water from the water jackets gets pumped through hot radiator fins, which don't cool it much, and the same hot water flows right back into the engine - watch that temp gauge climb.

The fan's job is to get that hot air radiating from the fins out of there so it can't keep the fins themselves - and therefore the water passing through them - hot. Which finally brings us to shrouds. I need a shroud for my V-8 TR6 project. Right now, the fan is whipping away gamely right behind it, but it's not cooling the radiator enough when the car is sitting and idling. That's because, as you mention, air from all other sides of the fan can move more easily than air that has to pass through that tight grid of radiator fins. Instead, the fan just whips up air all around itself and doesn't pull much through the radiator. (This problem diminishes when air from the car's motion rushes through the grille opening into the radiator fins.)

Attaching a radiator shroud confines the air moved by the fan to a fixed path. A shroud closes off the space between the fan and the radiator. Because the fan's blades are angled to pull air from behind the radiator, once the shroud is in place, that pulled air must pass through the radiator.

You're asking about the radiator sides. The shroud I envision for my V-8 TR6 will attach at the outer perimeter of the radiator all the way around and taper in to form a circle close to the ends of the fan's spinning blades. The shroud will be like a vacuum cleaner attachment with a mouth the exact size and shape of my radiator. As soon as it is attached all the way round, virtually all the air my swiftly spinning fan moves, like a vacuum cleaner pulling through the shroud, will be pulled over those radiator fins.

The sides of my radiator are not finned; therefore, it doesn't matter how much of the sides my shroud covers as long as it leaves no gap between the back most portion of the radiator's perimeter and the front of my shroud.

Sounds like your radiator sides are finned. In that case, I probably would cover the sides with the shroud so air is drawn through the front of the radiator. Running the shroud just up to the back of the sides would leave a small area of fin at that juncture with low resistance to airflow, which might cause lots of airflow around the periphery, and less through the rest.