Remember, the system is sealed, so whether you have a 1.4 bar or 2.0 bar cap, an overheating engine is going to expand into the ET which has a limited ability to relieve pressure before the entire system develops enough pressure to create a "new" relief (e.g., cracking the ET, blowing a hose, whatever is the weak point).

I have installed 1.4 bar caps on my BMW's, but as I've come to understand the system better, I'm not convinced it really makes much (if any) difference. The best thing you can do to minimize the chances of a pressure failure is to keep your coolant level at the minimum full level. I run mine with the top of the float stick just even with the top of the ET.

The more full you run your ET, the less capacity it has to absorb coolant/pressure from the system. Remember that the cap does not vent externally. It only vents to the ET.

AM.

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E70 2010 3.0 M57 AT Titanium Silver with Black Leather
E53 2004 3.0 M54 AT Toledo Blue with Gray Leather
E83 2008 3.0 N52 AT Silver Gray Metallic with Black Vinyl
E46 1999 2.8 M52TU 5MT Black with Tan Leather 250K+ miles (Sold, but not forgotten)