The shrouded radiator RPO was not available on any Advance-Design 3100 trucks, at least as far as it being listed in Truck Data Books and in Specifications Manuals.
The RPO-256 Heavy-Duty Radiator was available from 1947-1952 on 3600, 3800, and 4000 series trucks. I was 17.5 qts or 17 qts depending on the year (compared to regular 15 qts) and included a shroud for the fan.
Larger trucks (5000 and 6000 series) had a standard higher capacity radiator with shroud.
In 1953, there were two sizes of these H-D radiators with shrouds, the larger size was for 5000 & 6000 series trucks. This larger size H-D radiator became the standard radiator on 1954/55 5000 & 6000 series trucks.
