See full version: Outboard engine cooling system problems
As with any job, the first time you do it can be relatively slow, especially if the there’s electrolysis around the bolts securing the gearbox to the leg. But with practice it becomes a quick process to replace the impeller, so there's no excuse for not doing it every year.
Left: Unbolting the lower unit. Right: Splitting the lower unit away from the rest of the leg.
Outboard engine troubleshooting is a handy skill. While a fuel system problem may make it impossible to start an the engine, outboard cooling system problems have the potential to destroy an otherwise healthy motor as overheating can lead to a blown cylinder head gasket, or even a complete seizure of the engine.
Start by removing any encrusted salt from around the bolt heads – a kettle of hot water will do this, with the assistance of a soft brush if necessary. When dry, give the bolts a liberal dowsing of easing oil and leave for 24 hours. This may be enough to free the bolts, but don't be tempted to use excessive force. Heating the aluminium casing around the bolt threads with a blowtorch will cause the casing to expand a little, thus loosening its grip on the bolts. Even if this enables the bolt to be turned only a few degrees, the process can be repeated several times until the bolt has been removed. [links]
Outboard engine cooling systems can be the root cause of many issues, and it's key to fix outboard engine problems before they cause serious damage.
Generally outboard engine cooling system problems stem from a lack of basic maintenance – the impeller should be changed annually and engines used in salt water should be regularly flushed through with fresh water to ensure corrosion and scaling is kept to a minimum. Problems tend to stem from these two sources – failure of the impeller, or a partial blockage of the waterways by salt and calcium deposits.
Having issues with your outboard fuel system. Our inventory of Sierra carburetors kits and Nissan outboard fuel filters will have you backup and running in no time. These high-quality parts are specifically designed for Nissan outboard engines. To make sure engines continue to run smoothly make sure to complete regular maintenance including regular oil changes and tune-ups.
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RPM Information: 4500-5500
Your engine's RPM range is important in choosing the right propeller for a given application. For example, if you look at your tachometer at top speed and it is not within the engine's RPM range then that is generally not good. You want your RPM's to be within the proper range while at wide open throttle (WOT). Be sure to do your testing under your normal boating conditions and with a good propeller (not bent, cracked, or excessively chipped). [links]
The iboats Outboard Motor Forums are another excellent source of information.
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You can remove and visually inspect most parts of your clogged outboard, but not all. You can flush the cooling system with fresh water using a garden hose just as you do when you winterize the outboard. But some parts require a different approach. One example is the jets and passages in a carburetor, which are small, some verging on invisible. And a bit of dirt from contaminated fuel can be too small to see. Remove the carburetor, clean it in carburetor cleaner and reinstall it. Ensure all electrical connections are tight and the insulation on the wires is in good condition, because a short circuit can masquerade as a clog. [links]
A clogged outboard can be a nightmare. How much you experience that nightmare, depends on the nature, location and cause of the clog. For example, an outboard with a clogged cooling water discharge requires little or no disassembly, whereas an outboard that’s been underwater -- and laying in a mud bank -- needs a nearly complete disassembly. Unclogging an outboard begins with troubleshooting where to find the blockage -- a job for someone skilled in mechanics.
Troubleshooting starts with the obvious. If, for example, the motor fell off the boat, landed in the mud at the bottom of Lack-of-fish Creek and lay there for a week, you can pretty much assume you’ll have to disassemble the engine and remove the water and mud from all the tiny spaces in the carburetor, the cooling system and the cylinders. If the motor didn’t drop in the drink, start with the simple stuff that’s likely to clog, the air, water, fuel and oil filters. If water refuses to spray from the cooling system’s discharge hole at the back of the engine, run a stiff wire into the cooling water discharge tube, to remove items that may clog the hole, a common location for a clog. here
Pick up the shop manual and read the section describing the process you’re about to undertake. Manufacturer’s manuals provide a wealth of information on specific troubleshooting techniques and the methods for unclogging an outboard. They describe and illustrate all repair techniques for the specific engine, list the tools needed for a job and provide essential information for specific engines, such as torque specifications for tightening all bolts. Note this one caveat: not all are non-manufacturer repair manuals the same. Manufacturer’s manuals provide you the same information they give to a marine technician. Commercially produced manuals, although based on the shop manuals, may lack some necessary information altogether.
Before you undertake the process of troubleshooting and repairing a clogged outboard and after you read the appropriate section of the shop manual, decide if you’re confident about performing the repair. An outboard is a small engine that uses extensive or complex computer, electronic, electrical, mechanical, cooling or fuel systems. If you feel you lack the aptitude, the tools or the time to make the repairs yourself -- or you can’t find the problem -- don’t be afraid to take your outboard to a qualified marine technician, as some new outboards can cost tens of thousands of dollars. If the cost of repairing your ailing outboard exceeds the cost of a new outboard, go shopping. But if the cost of repair is less than the cost of a new outboard, you’ll save money by going with a professional. [links]