Posted: November 1, 2012
Don’t wait for trouble to inspect your engine’s cooling system.Keeping your cool can be difficult when your engine temperature starts to rise. Fortunately, most overheating problems can be avoided by carrying out a few preemptive maintenance checks and procedures. Here are a few basic tips on maintaining both raw-water (open) and recirculating (closed) cooling systems.
Start with the through-hull intake, making sure it’s clean and free of obstructions (trash, barnacles, weeds, etc.) that could block or restrict water flow. If it’s covered with a scoop strainer, remove and clean both the strainer and the through-hull intake, then give each a coat of antifouling paint to help keep them free of growth. With integral strainers, use a thin-blade knife or screwdriver to help crush and remove growth.
Next, test the seacock, ensuring that it’s fully operational (seacocks should be exercised monthly as a routine maintenance item).
Check the hoses on the suction side of the raw-water pump (seacock to strainer, strainer to raw-water pump) for problems such as deterioration, kinks and chafing. Suction side hoses must be wire reinforced to prevent them from collapsing at higher engine speeds (due to increased suction), a situation that can result in intermittent overheating. Verify each hose is double clamped where possible (see sidebar) and that each clamp is tight and free from corrosion, as loose clamps on the suction side can introduce air into the cooling system.
Verify that the sea strainer is securely mounted, free from leaks and that the basket (filter) is clear of debris.
Pull and inspect the raw-water pump impeller for deterioration, cracks, missing vanes (blades), etc. Missing impeller parts must be found and removed; otherwise, they can block portions of the cooling system, causing overheating. Annual impeller replacement (regardless of appearance) is a good way to avoid failure. You can keep serviceable units as spares.
While the pump is disassembled, check the cover plate and wear plates for excessive scoring, and replace if any is found. After servicing, reassemble the pump per manufacturer’s instructions, start the engine and verify there are no leaks.
Closed (Recirculating) System
Inspect the system for leaks, paying special attention to engine manifold and exhaust elbow joints, hose ends and freeze plugs. Check the hoses for leaks, kinks, chafing, bulges and deterioration, and give them a good squeeze to get a feel for their condition. You want them to be supple but not spongy. Replace those that are hard or emit a brittle, crackling sound.
Coolant should be monitored regularly for the correct level and replaced annually. It isn’t the antifreeze properties, but rather the rust-inhibiting qualities of the coolant that break down and require renewal.
Check both open and closed cooling pump belts for proper tension. Belts that are glazed or show signs of cracking or stickiness should be replaced immediately. Misalignment, which leads to excessive wear, is often indicated by the presence of black “belt dust.”
You don’t want to see evidence of drips and leaks while running, because that’s an indication of pump seal failure, so inspect both the raw-water and coolant pumps. Pump bearings can be assessed by removing the belt and rotating the pump pulley, while pulling it in and out and side to side. Looseness and rough operation are typical signs of pump-bearing failure. Pump bearings generally last a long time, but as pumps often share the same belt as the engine alternator, they can be exposed to increased belt tension, such as when upgrading to a high-output alternator, and greater wear.
Finally, verify the existence and location of sacrificial zinc anodes in both open and closed systems (heat exchange, engine). These should be checked regularly and replaced when they reach 50 percent wastage.