Coolant shouldn't expand enough to come out the top of reservoir. Even though you have to vent the pressure if the engine is warm. At operating temp there will be some normal pressure but if your coolant is concentrated enough it shouldn't boil at atmospheric pressure.

Did you dilute with distilled water when replacing the hose?

You should be able to run the car up to operating temp (use hidden menu or an IR thermometer on the upper hose to measure the thing on the dashboard is pointless).

Once warmed up, shut down and let it cool just a few minutes then slowly open the reservoir to vent pressure.

Then you use the tester and only vapor should come out no fluid. If fluid comes out suggests either the head gasket is blown or the coolant is diluted and boiling.


–awr–

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)