One observation I can share regarding the V6 is this:
The tank has two fill lines, one "FULL COLD" and one "FULL HOT".
Say the car is cold, and the coolant is at FULL COLD, operation is totally fine from here. Once the car has warmed up fully, coolant will not reach the FULL HOT line though; it'll be about an inch lower.
Now, with the car still hot, if you top off to the FULL HOT line, operation will suffer in that, with sloshing during normal driving, small amounts of coolant will seep from the tank cap and from around the sensor, evident through dried up greenish stains on top of the tank. Once the car cools down, the coolant will sit well above the FULL COLD line.
That's why I essentially ignore the FULL HOT line altogether. I check coolant only when the engine is cold, and only against the FULL COLD line. This way, I have no seepage and no stains on top of the tank.