I'm beginning to believe that you are indeed experiencing the symptoms of an impending head gasket failure...cooling components are functioning and maintaining proper engine temps, but excess combustion chamber pressure has managed to leak into the system.

It is probably marginal right now, but it will only get worse...I'm not the absolute expert here, but if this is the case, more driving could eventually cause the engine to overheat and possibly warp the head...you don't want that.

And if enough coolant spills into the cylinders, you could hydrolock the engine and maybe even bend a rod...more $$$!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car