The life of an exhaust system
Coolant loss is normal. Typically a BMW cooling system has a fill capacity of 6.5 litres. It is expected that in a 6 month period - coolant loss is about 15%. This is because the expansion tank has a cap that reliefs pressure at 1.4 bar.
So this would mean that about 900ml of volume may need to replaced. Best practice would be to replace the coolant and water in a 50/50 ratio. It is recommended that distilled water be used as mineral water contain elements that are not water pump friendly.
If a coolant loss issue is picked up by the technician then the next steps would be to isolate and determine where it has sprung a leak in the cooling system.
Starting off with a pressure test would be a good start. Exert a pressure of about 1.4 bar and keep your eyes peel for bubbling, noises or coolant traces. Since BMW coolant is blue - that would be easy to spot.
Follow the coolant hoses starting from the expansion tank. Make sure you look at the water valves, radiator, water pump and thermostat.
A good quality expansion would be able to hold at least 1.4 bar of pressure. Over time the seams and joints of the expansion tank would deteriorate. It is recommended that the expansion tank as well as the coolant hoses be replaced every 100k of mileage.
The pics of the expansion tank attached showed that it failed where the coolant level sensor connector is located. Leaking innocuously.
Expansion tanks sold by BMWPartsCo.com are of at least OEM quality and comes with a new coolant level sensor.
Punch in your VIN number on the site to find the expansion tank for your ride or chat with customer support to find out more information.
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