How to flush your outboard correctly and why it’s so important

Author: Stuart Buckingham   Date Posted:22 May 2017 

Blog How to flush your outboardOne of the biggest killers of the modern outboard is corrosion and often it's not what you see, but rather what you don't see that causes the biggest problems.

Outboards are raw water cooled and draw water directly from their environment to cool down. In fresh water, this is not a problem but in saltwater, it opens the engine up to salt build up and corrosion within the outboards internal cooling passages. The build up of salt over time can cause overheating issues or, worst case, corrosion that will eventually eat away at your engines block destroying your outboard.

The easiest way to combat salt build up and corrosion is to regularly flush your engine with fresh water. Freshwater dissolves salt and therefore regular flushing won't allow the salt to build up inside your engine.

Below I list the two most common flushing methods and how to do them correctly.

Ear Muff Method
'Ear Muffs' allow you to run your engine with fresh water using a standard garden hose to clean out both the block and water pump of unwanted sand and salt.

  1. 1.  Place ear muffs over water intake grill on lower unit/gearbox making sure they fit firmly
  2. 2.  Connect garden hose to ear muffs making sure that your hose fitting clicks on
  3. 3.  Ensure outboard is trimmed down to be as vertical as possible
  4. 4.  Turn on hose and check your hose is connected to ear muffs correctly and there is good water pressure
  5. 5.  Start outboard, making sure that your outboard is pumping water from tell tail
  6. 6.  Run outboard for 2 to 5 minutes to ensure the thermostat opens and fresh water passes through all internal cooling galleries
  7. 7.  Once completed, switch off your outboard and then turn off your hose.

Drum/Tank Method
When you have a small HP outboard (under 25hp) the lower unit may be too small for aftermarket flushing devices to fit properly. The engine manufacturers may have custom flushing devices but these can sometimes be expensive and tricky to fit. Creating a homemade test tank may be the best solution. They're easy to make (Bunning's wheelie bins make great test tanks) and they'll save you wasting litres of water every time you want to flush your engine.

  1. 1.  Back boat up to drum or tank
  2. 2.  Lower outboard into water, ensuring the water level is around 2 inches above the cavitation plate
  3. 3.  Try to make sure your outboard is as vertical as possible
  4. 4.  Start engine, run in neutral for 2 to 5 minutes allowing the thermostat to open and fresh water to circulate throughout the internal cooling galleries
  5. 5.  When complete, switch off outboard and remove from tank

I really can't stress how important it is to flush your outboard after every use. If you keep to a regular flushing routine you are giving your outboard the best chance of having a long and healthy life.

Comments (6)


By: on 29 May 2018
Hi , I just got an old half oil drum for this purpose but it still has a lot of oil residue it it, will a small amount of oil in the water hurt anything or do I need to thoroughly clean it out first ? Any tips on how to clean it ? thanks. Lynton

Outboard Spares Response
A little bit of oil shouldn't be anything to worry about but if you're worried a degreaser should clean it up pretty well before filling it with water.

Flushing outboards

By: on 25 July 2017
yea guys i do the taste test when flushing my motors after use as i can not see if the salt is gone , seems the best way to do it .


By: on 24 May 2017
we sometimes get away camping where there is no water to flush motor, sometimes we are away for 2 weeks, we cant flush motor till we get home, how much damage are we doing??

Outboard Spares Response
Your engine will be fine if you're using it almost everyday while you're away. The damage can start to take affect if the outboard was used and sat for a long period of time without flushing after use.

camping away

By: on 23 May 2017
I take a 20lt water tank with a 12v pump and fit my muffs to it and flush my motor every time It comes out of the water when away camping at the very least until I get home.

Outboard Spares Response
Sounds like a good system you've got and nice work saving water where you can.

Salt Away

By: on 23 May 2017
Is Salt Away a good option to run through my out board . If so how often should I run it through Regards Rob TRob R

Outboard Spares Response
Hey Rob, we actually haven't ever used Salt Away so we can't really comment on how well it works but people on our Facebook page have said good things about it. We tend to use plain old fresh water as soon as we can on our outboards and that works just fine as long as you flush it for long enough.

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