Also, be sure your batteries are topped off. Without water, the batteries can't hold a charge – and the water continually evaporates as you charge the battery. Use distilled water and keep a funnel with a short hose handy to pour the water into the cells.
In addition, be careful not to overcharge your batteries. Many boaters leave their battery chargers plugged in all the time, hoping for a fully charged battery for their next run. With a modern digital charger, this may present no problem. But before the mid-1990's, all battery chargers were built to continuously trickle charge at 3 amps, which can ruin a battery in six months. If you have an older boat, you may have an older charger as well, which will mean you will have to disconnect it after charging to avoid damage to the batteries.
If the battery juice seems too low to crank the engine, there are a few tricks to get started. Run jumper cables from the battery terminals to the engine and the starter, in parallel with the battery leads. This doubles the pathway and halves the resistance, causing more current to flow. Make sure you know where to connect to the positive lead on the starter, and connect the negative lead to the block as a ground. Adding the jumpers allows additional pathway for the current, which reduces the overall resistance proportionately.
I did this every time I started one of the engines on a commercial charter vessel, which had unusually long battery leads to one of the engines. The owners did not want to buy larger cables so the jumpers became standard.
When away from the dock and the engine won't start, another trick is to stop and clean all the battery terminals and connections. Often salt has gotten in to create more resistance than your battery can handle. Once everything is clean, add a set of parallel jumpers and try starting again. More current will flow from your weak battery and the engine may just turn over.
ADEQUATE COOLING
Marine diesel engines are cooled using sea water (sometimes called raw water) and fouling from salt cake and marine organisms can be major problems.
The solution is to flush the system with fresh water as often as you can. Prior to starting the engine, back-flush the sea water intake by connecting the fresh water hose from the dock – this requires a fitting atop the sea strainer, or elsewhere in the cooling line – and forcing water to flow backwards out the seawater intake. This simple action will remove all the marine organisms trying to colonize. If successful, the little critters can prevent the flow of the necessary cooling water.
After shutting down, flushing the engine-cooling jacket with fresh water will help prevent salt cake and corrosion on the engine interior. Close the seacock and use that same hose connection to flush fresh water through the engine. It is not a good idea to run the engine using fresh water from the hose. Usually, a hose is small compared to the engine's raw water intake, and may not provide enough cooling for the engine. Sometimes, when an engine is being tested ashore, a garden hose is used this way, but the engine should never be put under load or operated at higher than idle.
CAPT. ALAN R. HUGENOTOnce a year, replace the raw water pump impeller, which is the bladed rubber cylinder in the water pump that pulls sea water into the system. Install the spare you have on hand, and purchase a new spare. Sand particles get into the pump when a boat operates in shallow waters near shore. These particles wear out the impeller, which will then starve the engine of cooling water and cause it to overheat.
To change the impeller, close the seacock, locate the pump housing (check the manual or run back your cooling line) and remove the plate. Check which way the blades are turned, then pull the impeller from its housing. You may want to use a removal tool – Jabsco and other manufacturers make them – rather than a wrench, to avoid breaking off pieces of the impeller inside the housing. Slide the new impeller in place, with the blades facing properly. You might want to use a little dish soap to ease the insertion. Check the condition of the O-ring sealing the plate and replace it if necessary, then fit the plate back on and tighten it (remembering you want to remove it again next year. Run the engine and insure that cooling water is flowing out the exhaust as normal.
Changing the impeller can be difficult, because the housing is placed in a tight location on many boats, making it difficult to access. Working with tools and seeing what you are doing can be a challenge. But your engine cost thousands of dollars and it is worth the effort. You can purchase several items that can make this easier, such as an impeller removal tool and a Speedseal, which is a replacement for the housing cover that is self-seating and uses handcrews that can be manipulated without tools. (For a story on Speedseals, see link below).
Be sure to clean out the raw water strainer periodically, which can get clogged with debris brought in with the cooling water, and to exercise the seacock that controls the flow by opening and closing it. This insures that the valve works and is not frozen or clogged.
