Okay, I've been meaning to start this thread for a couple of days - in another thread I was talking about some problems (dropped valve seat) that I incurred recently on cylinder 5. I've heard several times that #5 is problematic due to water flow issues, and johnc posted the following in that thread:     Now, my car is still street driven and I'm a bit concerned about running cooling system pressures that high for fear of blowing out my heater core - anybody know if that