LT1 Fan Temps and Pressures

So I found this chart info below, and thought it might help others that were concerned about their fans both coming on.

B/D-car LT1 (Caprice/Impala/Roadmaster/Fleetwood) Cooling Systems:

Standard equipment for all LT1 equipped B/D-cars is a dual electric fan setup with a 150-watt primary (RH) fan and a 100-watt secondary (LH) fan. The electric engine coolant fans are independently operated by the PCM (Powertrain Control Module) based on the inputs from the Engine Coolant Temperature (ECT) sensor, A/C Pressure Sensor, Vehicle Speed Sensor (VSS), and various other inputs.

The B/D-car coolant fans operate under PCM control at the following engine temperatures and A/C system pressures:

Fan Mode ... Temp ... Pressure

Primary (RH) Fan ON ... 109°C / 229°F ... 189 psi
Primary (RH) Fan OFF ... 105°C / 221°F ... 150 psi
Secondary (LH) Fan ON ... 112°C / 234°F ... 240 psi
Secondary (LH) Fan OFF ... 108°C / 227°F ... 210 psi

Additionally, the PCM will turn off the fans at higher vehicle speeds (above 48 MPH I believe) since running fans can actually impede airflow through the radiator at high speed. Each fan also has a minimum running time. Once activated, the primary fan will run for a minimum of 50 seconds, and the secondary fan for a minimum of 26 seconds. Finally, certain Diagnostic Trouble Codes (DTCs) may cause the PCM to turn on one or both fans.

Hope that helps!

-Texas Mike