Transmission Fluid and Coolant Maintenance Questions

[smackboy1]

The manual states that the transmission and differential fluids are supposed to be changed at 90K miles and the coolant is never changed. Is it good practice to change out the tranny and diffy oil and coolant after a certain number of years regardless of miles? Can it hurt anything (except my wallet) to prophylactically change these fluids at say 4 year intervals? I only drive on the street, but I have no idea how the car was driven the 4 years the original owner had it.

[viper501]

Change the fluids... the technology has gotten better but the real reason for the increased service intervals is the companies like JD Power that provides data on cost of operation. Various manufacturers, Mercedes, BMW, etc, have increased service intervals to decrease the perceived cost of ownership. Frankly, it is a huge disservice to the buyer but it typically won't affect the manufacturer as failures will occur after the expiration of the relatively short time frame for warranty coverage.