Diesel, How Much Radiator Should Be Blocked Off
 

New today to the site. Have been observing from a distance. 2004 Dodge Diesel: how much of the radiator is acceptable to block off for the winter ?
Would assume that one might block off between the intercooler and the radiator. Or would the recommendation be to block off on the outside of the grill as the OTR semis do?

You're going to have to discover the first answer for yourself, since much depends on your individual grill shape, winter temperatures, and type of driving. Your second question is easier. Block on the outside to smooth the airflow around your truck.