V8 uses a two speed fan. V6 uses a single speed fan.
If a single speed fan is used in a dual speed application, the fan will run only on low speed. The fan would shut off when the PCM called for high speed fan. Overheating is the result.
If a dual speed fan is used in a single speed fan application, the fan will run only on low speed. The V8 low speed fan is slower than the V6's.