Boating Tips


Posted 6/2/2010

Because it is not seen on a daily basis, your outboard's cooling system can often be neglected. The cooling system, however, is critical to the outboard's health, and a clogged system can cause outboard performance issues.  Just like the clogged drains seen on TV advertisements, your outboard's cooling system can also become clogged with debris. But rather than pouring liquid into your outboard like you do into a clogged drain in your sink, you need to perform a simple freshwater flush to clean out the cooling system.  The only equipment you need to perform a freshwater flush is a regular garden hose. It's a simple, inexpensive process that can make a big difference in the performance of your outboard.

Most of us take good care of our marine equipment – we wash and wax our boats and outboards, change the oil and oil filter regularly, and replace the fuel filters religiously.

But what about your outboard's cooling system? Unfortunately, it's one of those out-of-sight, out-of-mind things we tend to take for granted and often overlook in our maintenance regimen.

During the course of one boating season, the water pump can suck up mud, sand, and silt, which then flows through the engine. Over time, this debris can accumulate in the outboard's plumbing, eventually restricting the amount of water available to cool the engine.

This is a stretch, but we've all seen those ads on TV showing a plugged up drain; the plumbing in your outboard's cooling system can get just as clogged. However, unlike your bathroom sink, there isn't a magic liquid you can pour into your outboard to clean the pipes – that's where freshwater flushing an outboard comes into the picture.

Freshwater Flushing?
Freshwater flushing is just another way of saying washing out your outboard's plumbing with fresh tap water, usually via a garden hose at home. The clean water will dislodge most contaminants (sand, silt, mud, etc.) and force them out of the passages in the cooling system.

Tell Me How
The freshwater flushing procedure for your particular outboard should be clearly spelled out in the outboard's owner's manual. Here are some general facts about freshwater flushing.

Generically speaking, there are a couple of ways to flush an outboard – use the freshwater flushing attachment built into the engine (the water flows from the top down) or a flushing attachment, flush muffs in boat speak, (the water flows from the bottom up). Either way is fine; here are the major points for each method:

Built-In Flushing Device

• A built-in flushing device is a hose fitting, usually located near the lower rear cowling.
• Don't run the engine during this procedure.
• An outboard can be flushed with the boat on a lift (or in the water, it works best if you can trim the engine up so the gearcase is out of the water).
• Connect a garden hose to the outboard's flushing device fitting.
• Turn on the faucet, let freshwater run through the outboard for 10-15 minutes.
• Turn off the faucet, disconnect and roll up the garden hose.
• Put the cap back on engine's flush fitting (per owner's manual).
• The job is done.

Flush Muffs

• Flush muffs are rubber cups that fit over the water intakes on the gearcase (one of the cups has a hose fitting).
• They require running the engine (but only after you turn on the garden hose).
• This is best done with the boat on a trailer, or a lift completely out of the water.
• Trim the outboard to the vertical position.
• Screw the garden hose onto the flush muff connector.
• Place the flush muffs over the water intakes on gearcase.
• Turn the water on slowly, until you can see a bit of water leaking from around the flush muff rubber cups.
• Check to ensure the rubber cups are still in place over the water pickups.
• Start the outboard and set the throttle to no more than a fast idle.
• Watch for water coming out of the tell-tale tube at the lower rear of the cowling (the flow could be a steady dribble – that's OK).
• Get out of the boat and double-check that the flush muffs are covering the water pickups.
• There should be some water exiting the back of the gearcase, through the propeller.
• Run the engine for 10-15 minutes.
• Stop the engine and turn off the faucet. 
• Put the garden hose and flush muffs away, and you're done.

Flush Muff Method Warnings

• Never run the engine without cooling water. Turn the freshwater on before starting the engine, turn the water off after stopping the engine.
• Don't rev the engine while using flush muffs, because there isn't enough water flow/pressure to sufficiently cool the engine at high rpm.
• Running the outboard with little or no cooling water will cause expensive overheating damage in a very short time.

Flushing your outboard with freshwater on a regular basis can go a long way in extending the engine's life span – especially for those who boat in saltwater or plow through mud and sand a lot.

Freshwater flushing is easy and cheap – two words not often associated with the boating lifestyle – so keep the garden hose handy and keep 'er clean.