Johnson Outboard Cooling System

Johnson Impeller

Johnson makes some of the finest outboards on the water. However, the “health” of your boat’s power plant should be a primary concern and the part you check most carefully during your post trip maintenance routine. Key to the continued top performance of your outboard is the engine cooling system. Engines rev at high RPM and can overheat if pushed past their limits. Repair or replacement can be costly so keeping your engine’s cooling system working optimally is of primary importance.

The cooling system on an outboard is a very simple and compact application. Water intake is through the lower unit via water pump impeller. It is then forced upward to circulate throughout the powerhead, and eventually exits through the exhaust system. There are a couple sections of the outboard cooling system that require routine maintenance, so be sure to post-trip check the following.

Two key parts of your Johnson cooling system that need regular maintenance or could cause problems are the impeller and the thermostat. If your outboard overheats, a faulty impeller is most likely the cause. It is rare that a thermostat fails, but it does happen. If you find that a thermostat is not functioning properly, it must be replaced. Boat thermostats are not like automobile thermostats, which, when they fail, can simply be removed.

If you find that you need a replacement Johnson impeller, Wholesale Marine is the place to call. And if the thermostat proves to be the culprit, we carry the replacement for that too! Just be sure not to run your boat until this part has been replaced. If an outboard is operated without a thermostat installed, poor performance and internal damage will likely occur.

An outboard is designed to operate at specific engine temperatures, and if it does not obtain that temperature, it will run very sluggishly. Without temperature control the fuel/oil mix will not burn efficiently, which causes excessive carbon buildup. Carbon buildup in an outboard will cause piston ring problems as the rings will stick inside the piston ring grooves. Once the pistons touch the cylinder wall, immediate scoring will result. Once a piston is scored, it is only a matter of time before the powerhead is completely destroyed unless it is caught in time to perform an overhaul.

But it doesn’t have to be that way. If it has been determined that your Johnson outboard impeller in your outboard’s water pump requires replacement, this is a task that can be performed in a couple hours by a seasoned DIYer. Here is a brief overview:

1) Drain oil from the gearbox.

2) Remove the four nuts from the lower unit. Lift the unit clear and place to the side.

3) With the pump proper now exposed, slide off the seal, which sits on top of the pump housing.

4) Unscrew the bolts holding the pump housing in place and remove the pump housing.

5) Separate the pump housing and move it up the shaft. Be sure to include the bottom plate as well.

6) The new Johnson impeller can now be removed and replaced with a new Johnson outboard impeller. Note: The new part will have straight vanes. These will develop a set over time and through use.

7) Parts may now be replaced in reverse order or additional maintenance performed.

For more detailed instruction, please speak with our staff! Here is some additional advice on how to protect your Johnson outboard impeller by protecting your outboard’s cooling system.

Simple Steps to Protect Your Engine’s Cooling System

● Perform routine maintenance and by being responsive to warning signs such as a sluggish engine.

● Be sure to change your water pump without fail EVERY two years regardless of usage.

● If you operate your boat in saltwater, you must flush your engine and cooling system after every use.

Following these simple guidelines will protect your marine engine from serious damage, and the mechanical skills required are fairly minimal. If you should have any questions, feel free to contact us at Wholesale Marine.

Wholesale Marine wants to be your one-stop shop for boating supplies! Contact us to talk about the cooling system on your Johnson outboard. Our knowledgeable staff shares your passion for life on the water. And our friendly customer service will make you a Wholesale Marine customer for life! We offer same day shipping and our low price guarantee, call today (877) 388-2628.