Question

2006 BMW 325i 3.0L with code P0128, new thermostat, new radiator. code still comes up the next day

Answer 1

P0128 Coolant thermostat malfunction

What the coolant mixture? is it it just plain water?

 When it comes to BMW you need the proper coolant mixture. The owner of this vehicle replaced the thermostat and used plain water. The fix drain the water add the proper coolant. If the proper coolant is mixure is  added clear the code, the engine will go thru a readaptaion

Answer 2

P0128 BMW Code - Thermostat Low Coolant Temperature

Read more: https://www.autocodes.com/p0128_bmw.html