That's not why a shroud works.
Just sayin,
It pulls the air better because the fan is surrounded, AND uses the entire core area to pull air through instead of just where the fan is.
Actually it's all of the above wouldn't say? I didn't want to get all technical. I've read what I stated online somewhere. I mean you really would have to be an idiot not to think the air isn't coming through the radiator core and blowing on the engine. lol
