BMW 525i Problem Report
BMW 525i Check Engine Light and/or Engine Overheating
The thermostat may fail resulting in engine overheating and/or illumination of the Check Engine Light. Replacement of the thermostat along with a complete inspection of the cooling system will be necessary to correct this concern.
Overheating can cause severe engine damage. If the engine begins to overheat it is recommended to stop at the first available location and have your vehicle towed to a repair shop.