Did a cooling system flush.
After the flush filled it with 1 gallon of MB Original Antifreeze and 1gallon of distilled water.

Still having the same symptoms.
While on the highway, I can keep engine ~ 100C, however on long traffic lights temperature is getting really high.

During the flush I checked for spots of oil in the coolant, however everything was clean, I also checked for pressure buildup in the upper radiator hose (when engine is still cold) and did not notice any pressure there.

I need to check for CO level in coolant, but I have no idea how to do this.
Can somebody give me an idea how to do this (what tool will I need to get)

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AlexS