BMW 1 Series Engine Problems

The B4820 two-litre four-cylinder engine in BMW's current F20-generation 120i uses a timing chain.

The current F20-series BMW 120i is rated on a combined cycle as using 5.9-litres of unleaded fuel per-100km. While it isn't as good as other small hatchbacks in the class it would still be considered good fuel consumption, especially given most large family cars would consume 10-12-litres per-100km.

BMW's F20-series 120i runs a timing chain on the B48B20 two-litre four-cylinder engine.

Your car is out of warranty, so you would have to make a goodwill claim for BMW to replace the bottle free of charge. I think they should come to the party with the cost of replacing the bottle, and by all means try that, but I doubt you will be successful. There are many plastic components used in the cooling system on BMWs, and like the expansion bottle on your car they all eventually give trouble. In my view it's poor engineering.

The official fuel consumption figures for BMW's 120i on a combined cycle is 5.8L per-100km driven.

I would certainly consider this good consumption as many large cars use nearly twice as much fuel per-100km.

An older BMW I know of doesn't use any oil at all between services, but I'm told that it's quite common for the newer engine like yours to burn oil. It's generally held that a consumption of up to 1 litre per 1000km is normal. If you are concerned that yours might be too high do a check of the actual consumption. That way you know for sure how much it is burning.

The engine is probably worn and needs honing and new rings.