The thermostat regulates the temperature of the engine. If you keep the same t stat there should be no change in engine temps. The z3 s54 radiator just gives extra coolant capacity and exchanges the heat more effectively. So the cooling system has a greater thermal reserve if you decide to push the car harder. I run the S54 rad in my m54 coupe and I deleted the mechanical fan, I did not replace the mech fan with an electric unit. __________________ ~Dave~ 98 328ti Morea Grun slicktop 11 128i space gray slicktop 13 JGC WK2 Deep Cherry Search | RealOEM |