I was having systems of a blown head gasket on my M3. My cooling system was pressuring within minutes of starting the car. The car runs great and doesn’t over heat whatsoever even with our 105 degree weather.
So I decided to take the cooling system back apart and inspect the orings and water pump gasket to see if they were causing the issue. I changed out all 4 of the orings behind the water pump with some Viton Orings. This fixed the problem.
Turns out ECSTUNING sent me two different sizes for the two orings on the small hard pipes, one 16x3 and one 18x3. The 16x3 oring was on the lower hard pipe that comes from the expansion tank and was sucking air causing the system to pressurize. It also caused major cavitation and was eating up the inside of my Brand New water pump and Tstat.
I wasn't too happy having to tear apart my entire cooling system again due to a undersized Oring but at least it wasn’t a blown head gasket.
Orings replaced are in Red.
16x3 and a 18x3mm Oring!
New vs Old Tstat
New Viton Orings