Sterndrive Power Steering Hoses and Fluid Cooler: Inspection and When to Replace

Shut the engine off, take the key out and let it cool. Turn the battery switch off if you'll be leaning near the starter or alternator. Open the engine hatch and air out the compartment; on gasoline engines, sniff for fuel before doing anything else and stop if you smell it.

Check the power steering reservoir as your manual describes. Wipe a drop on a white paper towel:

• Clear red or amber: normal for many systems.
• Dark brown or burnt smell: old or overheated fluid.
• Milky, pink and cloudy, or foamy: water or air in the system. On engines with a cooler, a failed cooler is one of the causes. Have it checked.

Write down the level so you can tell later whether it is dropping.

Look under the engine, the pump and along the hose route for red or amber oil, or an oily film on bilge water. Lay a white paper towel in suspect spots overnight. Don't pump oily bilge water overboard: it is illegal to discharge oil that leaves a sheen. Soak it up with oil-only absorbent pads and dispose of them as your marina or local hazardous waste site says. If you see a sheen on the water around the boat, report it to the National Response Center at 1-800-424-8802 (see our bilge oil cleanup guide).

With a flashlight and mirror, follow each hose from the pump to the transom and back. Boating Magazine's checks say hoses should feel pliant and firm, not mushy, brittle or dry-rotted. Look for:

• Cracks in the cover, especially at bends
• Bulges, blisters or soft spots
• Shiny or flattened spots where it rubs the engine, a bracket or the hull
• Hoses touching or very close to the exhaust manifolds, risers or the belt
• Tight kinks or sharp bends. The NTSB traced a towing-vessel fire to a hydraulic hose bent tighter than its minimum bend radius; it ruptured and sprayed oil on a hot exhaust.
• Missing or broken support clips that let a hose sag or swing

The metal ends are where most old hoses fail. Check every crimp at the pump, cooler and actuator:

• Light surface rust that wipes off: clean it, coat it with a corrosion inhibitor and keep watching.
• Flaking or bubbling rust, pitting, or rust creeping under the crimp: the hose assembly is near the end. Plan to replace it.
• Wetness or caked oily dirt right at the crimp: the hose is weeping there. Replace it.
• A hose that has moved or pulled partly out of its end: stop using the boat and replace it.

Don't try to re-crimp, clamp or wrap a leaking high-pressure hose end.

Look at the nuts where hoses screw into the pump, cooler and actuator. A wet nut can mean a loose fitting or a failed O-ring or flare. You can try snugging a weeping fitting very gently with a proper line (flare-nut) wrench, holding the mating fitting so nothing twists. If it still weeps, or the fitting is cracked or rounded, stop: overtightening can crack fittings or the pump body. That's a pro job.

Find the cooler (often near the front or side of the engine, or on the transom assembly, in line with a raw-water hose). Check:

• The body and end caps for heavy corrosion, green or white crust, or pin-sized wet spots
• The raw-water hoses and clamps on it: tight, not cracked, no rusty or broken clamps. Many cooler "leaks" turn out to be a loose hose or clamp at the cooler.
• The steering fluid connections on it for weeping

Signs the cooler is failing inside: the fluid level keeps dropping with no drip you can find, an oily sheen comes out with the exhaust water, or the fluid turns milky. On many sterndrives the cooler is one of the first parts the incoming raw water reaches, so leaves, weeds or broken impeller vanes can lodge there and cut cooling flow. If your engine has started running warmer, ask your mechanic to check the cooler as well as the impeller (see our overheating guide). A failed cooler is normally replaced, not repaired.

Clean the hoses, fittings and cooler with degreaser and wipe them dry. Then, with the drive in the water or cooling water supplied the way your manual says (never run a sterndrive dry), start the engine. Have your helper turn the wheel slowly lock to lock a few times while you watch from a safe distance with a flashlight, keeping clear of the belt. Watch for hoses that jump or flex a lot, drips forming, or fluid misting. Don't hold the wheel hard against full lock for long. Shut down and look again closely with the engine off.

Put a paint-marker line or tape tag on any suspect spot, lay an oil-only pad under the pump and cooler, and recheck the fluid level and pads after the next few runs. A small weep that never changes is a watch item; a level that keeps dropping or a pad that soaks through is a repair item. Some leaks only show when the system works hard: a hose end or cooler connection that stays dry at the dock can push fluid out during sharp turns under way. If the dock test finds nothing but the level keeps dropping, check the pad and fluid right after a normal run that included some full turns. Log what you found in BoatMend with photos.

Plan replacement when you see any of these:

• Flaking rust at a crimp, weeping at a crimp, or a hose pulling out of its end
• Cracks, bulges, soft spots or chafe through the outer cover
• Fluid leaking overboard, milky fluid, or a corroded or leaking cooler
• Hoses that are original on an older engine and getting stiff, even if dry

Many owners replace both steering hoses and the cooler together on older engines, since they age together.

Replacement hoses must have the correct pressure rating, ends and length for your engine: use the maker's parts or have assemblies made by a hydraulic hose shop to match. The system must then be filled with the specified fluid and bled to remove air. The cooler connects to both the steering and the raw-water circuits; a mistake there can cause a leak, overheating or water coming into the boat. Unless you're experienced with this exact engine and have the service manual, have a dealer or marine mechanic do it, and ask whether any service bulletins apply to your engine's serial number.

After any hose or cooler work, check the fluid level, run lock to lock, and look for leaks after the first trip and again after a few hours. When you winterize, make sure the cooler's raw-water side gets drained or protected with the rest of the cooling system as your manual says; water left in a cooler can freeze and crack it (see our sterndrive winterizing guide).