2013 GL550.

Initial problem was coolant was overflowing out of the designed vent hole in the coolant reservoir (especially during long drives) There is something causing the coolant to come out of the reservoir.

Reservoir has been replaced 3 times, twice with OEM and third time with genuine MB Parts. Radiator, radiator hoses, all 6 turbo coolant lines, coolant reservoir recovery tank hose, water pump, and thermostat was replaced along with all idler pulleys and drive belt.

The car was taken to 3 Mercedes Benz Dealers and they all diagnosed it as either water pump or turbo coolant hoses. They did a block test and it passed.

Does anyone have any insight before I spend anymore...
Thanks

 

My guess would be intercooler pump.

 

How about reservoir cap?

 

Before spending any money there is a combustion leak test, basically it test gases coming out of coolant reservoir for blown gasket.

 

Does your upper radiator hose still feel pressurized when the engine is overnight cold?
In other words, is there still pressure in the expansion tank when the engine is absolutely cold, like not run for overnight?
I love free tests.