As the separated IC heats pressure rises, pick a pressure you like I assumed the max of 16#.
( When you shut the car off the the pressure would still be present on the inside. What's radiator pressure, 16psi? - earlier posting ).

The -14psi is the number when your off the throttle, i.e. -25 -28 inches of mercury, I idle at -20+ inches.

So you can move the numbers, but I have 0 psig on the IC circuit. and thus lower differential pressure. The highest pressure difference is wide open throttle ( boost is high ) throttle, and IC tank pressure. In my analysis, I assumed the worst for most of the cars - NON ISOLATED IC running 16 psig and Idle or off throttle vacuum ( partial pressure ) which approaches 30 psig differential.

Worst, the pressure varies greatly in time, it can be zero differential to + 30 psig on the I/C many times in seconds in spirited driving. Again, I have the pressure differential that varies from + 15 psig and zero psig between the air and water circuits.

I still put forward the idea of electrolysis weaking the walls / joints due to chemicals and or currents thru the liquid circuit - charging current, starter current etc. I have water pump lube and conditioner added to my 25% ANTIFREEZE SOLUTION in the I/C curcuit.

HUMMMMM, I will have to see if my water has a Ph of 7.0 or not????
Weekend ENJOY. Woody