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the blue caps prematurely start to vent, a telltale sign is coolant residue around it. biggest problem with this is the drain for the expansion tank usually moves and dumps onto coil pack #1, the result is a cracked coil and misfires if it's not caught. the black cap is the porsche update which seems to be the fix, I have seen this countless times at our shop, but being florida we probably see more than cooler climates.....i have seen black caps vent prematurely, but most every blue one I've seen fails.

you can easily move and secure the overflow drain tube away from coil 1.....