Mercury - Power Steering Cooler Steering System Component Marine-Grade Cooling Assembly 8M0125858. Overview. There's something reassuring about a boat that responds instantly when you turn the wheel. Whether you're easing into a tight marina slip or settling into a long cruising stretch, smooth steering just makes the entire experience feel better. And when you know your system is protected from heat and stress, you can relax and enjoy the ride instead of worrying about how the engine's working