Sterndrive Power Steering: Fluid Checks, Hard Steering and Leaks

Write down when it happens: engine off or running, idle or speed, turning port or starboard, cold or warm, after launch or after sitting. Listen for whining or groaning when you turn. These notes save hours for you or your mechanic.

Find the power steering reservoir. On many MerCruisers it's the cap on top of the power steering pump on the front of the engine, driven by the belt. Don't confuse it with the drive gear lube monitor bottle or the trim pump reservoir, which look similar. Wipe the cap before opening it, then read the dipstick or level marks the way your manual says (some are read hot, some cold). Boating Magazine's engine checklist includes power steering fluid with coolant and trim fluid.

Put a drop on a white paper towel:

• Clean, the right color: fine.
• Milky or foamy: water or air in the system. A boat that sat for years, or a leaking cap seal, can let water in. Many sterndrive engines also run the steering fluid through a small cooler that sits in the raw-water (sea water) circuit; when that cooler corrodes inside, water can get into the fluid or fluid can be pumped overboard. A full fluid change and bleed is needed, and a pro should check the cooler.
• Dark and burnt-smelling: the pump has been overheating or running low.
• Low, and dropping between trips: there's a leak (step 5).

Add the specified fluid slowly to the correct mark. Don't overfill. If you had to add a lot, run the engine briefly (boat secured, drive in the water or with cooling water supplied), turn the wheel slowly lock to lock several times to work air out, shut down and recheck. Groaning that fades as you turn usually means air working out.

Clean the pump, hoses, fittings and the actuator area with degreaser, run the engine (drive in the water or with cooling water supplied) and turn lock to lock, then look again with a flashlight. Common leak spots are the hose fittings at the pump and at the actuator (older hoses often weep where the metal ends are crimped on, especially once they rust), the pump shaft seal behind the pulley, the steering fluid cooler if your engine has one, and the actuator or cylinder seals at the transom. Thin reddish oil under the engine after winter is a classic owner find: top up, mark the level, and watch it on the first runs before guessing which part leaks. Engine makers sometimes issue service bulletins about steering hoses or fittings, so ask your dealer whether any apply to your engine serial number. Running a pump very low on fluid can ruin it and overheat the fluid. Weeping fittings can sometimes be tightened gently; a leaking actuator or pump seal is pro work.

Engine off, key out. Look at the belt that drives the power steering pump. Boating Magazine says to press it between pulleys and make sure it springs back, and to look for cracks, glazing, dry rot, thin spots and black belt dust (a sign of damaged pulleys). Rusty, pitted pulleys can point to a water leak. A loose or slipping belt gives steering that goes heavy when you turn hard or at higher load, sometimes with a squeal. Adjust or replace as your manual shows. Mercury lists a spare belt among the parts to carry aboard a MerCruiser.

Serpentine belts: on many newer engines one long belt drives the steering pump, the alternator and often the raw-water or circulating pump, with a spring-loaded tensioner keeping it tight. If that belt comes off, steering goes heavy all at once and the engine can overheat within minutes. A BoatUS reader story describes exactly that on a twin-engine cruiser: the starboard tensioner failed, the belt fell into the bilge, and the couple had to get home on one engine with manual steering. With the engine off, look at the tensioner: the arm should hold firm pressure on the belt, the pulley should spin quietly, and the belt should sit squarely in every groove. A wobbly pulley, a weak arm or a belt riding off the edge means a new tensioner or belt before the next trip. If a belt comes off under way, shut that engine down and see the overheating guide before restarting.

With a helper watching the drive, turn the wheel lock to lock with the engine off. It will be heavy, but it should be smooth and even, with no binding, clunks or tight spots. Boating Magazine says to steer lock to lock and check the cable for binding or stiffness. If it's stiff or notchy with the engine off, the problem is mechanical: go to step 8.

The helm cable is the most common cause of stiff steering on older boats. With the engine off, look at the cable from helm to transom for kinks, tight bends, cracked jacket or rust at the ends. Clean and grease the cable end and the exposed ram as your manual allows; Boating Magazine also says to clean crud off steering rams. Southern Boating notes a worn helm can make even a new cable stick or jump, so pros often replace both together. On many sterndrives the cable connects to the actuator through a fitting that must be correctly aligned; if you've had the drive off recently and the steering changed, have the connection checked.

A boat that pulls one way or steers harder one way only at speed may be fine mechanically. A single prop's torque pulls the boat to one side, and drive trim and trim tab settings change how strong that pull is. Before blaming the pump, try different trim angles. If the boat steers evenly with the drive trimmed differently, it's a setup issue, not a failure. Big changes after a prop swap are a strong clue.

Stiffness in both directions with the engine off, plus grinding or rumbling when turning, can come from the drive and gimbal area, such as a dry or failing gimbal bearing or water in the bellows. See the bellows and gimbal guide. Mercury also notes engine alignment and coupler lubrication need periodic checks on MerCruisers.

After the fluid, belt, cable and drive check out, the remaining suspects are hydraulic:

• Hard one way only with the engine running, smooth with the engine off: often the actuator's control valve or its cable connection.
• Heavy both ways at idle, whining pump: low pressure from a worn pump or a blocked line.
• Steering that kicks or jerks on its own: air in the system or a sticking valve.
• Fluid leaking from the actuator body: worn seals.

These need pressure testing, special tools and correct bleeding procedures. Leave them to a pro.

Any time the system is opened, air must be bled out as the manual describes. Then test at low speed in open water first: turn both ways at idle, then at moderate speed, and check the fluid level again after it cools.