its a bit that sucks BEFORE the engine blows!
Some go to great lengths to ensure the VW engine is sealed air tight. Here's a photo of using thin foam to seal the dog house's tin covering to the shroud. Many installations are missing the lower tin piece directing the oil air exhaust and its rubber gasket. This allows the fan to such the oil cooler's exhaust air back into the cooling airs intake fan.
Many favor aftermarket shrouds too - many are just metal shells. Those that have disected stock shrouds (Jake Raby had a study out years ago when he was designing his DTM shroud) found that many aftermarket ones did not have the air directing vanes of the stock ones. http://www.volksbolts.com/faq/cooling.htm
Another area of discussion is the fan itself- the width, number of blades as well as balancing and welding of the blades (for higher than stock RPMs). Then there "do you add" the air velocity ring like was used in the 356 engine?
