I would think an inside steam issue would be a heater core problem. But make sure you weren't just getting some through the vents. Once you get the overheating issue sorted out, check for steam again.

Usually, water pumps leak from the weep hole, as a warning sign it's about to fail.

Your cap should be a 1.2 or 1.4 bar, (17.4 and 20.3 psi, respectively), so you have a "weak" cap if it's 15 psi.

Make sure you have the correct amount of water and a proper pressure cap, see what happens.

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