A thermal management unit for a vehicle powertrain includes an integrated oil heater, a control valve, and a pressure relief valve. A remote oil cooler is connected to fluid ports of the thermal management unit. Transmission oil is received into the thermal management unit and is directed to one or both of the transmission oil heater and the transmission oil cooler. A portion of the flow of oil can be internally bypassed through the pressure relief valve to maintain the pressure of the oil below a threshold. The flow of oil is directed through the control valve after having been heated and/or cooled, and the proportions of oil being directed through the oil heater and the oil cooler are determined by the temperature of the oil in the control valve.