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 (16)

225 Yamaha flushing fuel off or turn key off

By: on 29 November 2018
I have a 225 fuel injection Yamaha when flushing motor is it better to turn fuel off tell it runs out or turn it off after 5 minutes with the key .

Outboard Spares Response
Thanks for your question. Just run your engine as you normally would at idle while flushing your engine out. There's no real need to run the engine out of fuel. Cheers

Flush test

By: on 8 November 2018
Tasting the water from the tell tale does not indicate a flushed motor.The open thermostat indicates a flushed motor so the motor must be run until it is warmed up and the thermostat opens.The engine passages could still be constricted but if it is not overheating you are right to go.

Termostat

By: on 3 November 2018
Ho do you know when the thermostat has opened

Outboard Spares Response
Thanks for your question. When water begins coming out the exhaust relief outlets on the exhaust housing that's when the thermostat has opened.

salt away

By: on 1 November 2018
a big rapp for the salt away, I use a cap full in a drum, then another quicker flush with straight fresh water, the makers also recommend doing this

Yamaha flushing coupling

By: on 1 November 2018
My Yam 60 4 stroke has the 3/4" flushing coupling. I understand these were partly supplied for moored motors to allow them to be flushed. I have been told that these flushes don't get to every part of the motor particularly the water pump. I always start the motor but only briefly while flushing to make sure the water pump gets flushed. When I did put a pump kit in the pump it was as clean as a whistle.

Vinegar

By: on 1 November 2018
Ive heard vinegar is a great salt away to wipe down clean salt from power head etc leg and all those difficult places a hose just can wash

Running the engine dry

By: on 1 November 2018
We have 3x 25hp for inflatable surf rescue boats, we have been told to pull the fuel line from the engine to while flushing it, to run it dry. Is there long term problems with doing it this way? What would be the pros vs Cons - cheers

Outboard Spares Response
Thanks for your question. There are varying opinions on running a 2 stroke pre-mixed engine dry. Many believe that doing this often can cause wear on the cylinders of the engine over time.. Two stroke engines require that are pre-mixed get their lubrication from the fuel mix. Therefore it is said that running them dry of fuel is starving them of lubrication. Obviously this is more a problem at High RPM rather than Low RPM. If you are wanting to remove the residual fuel in the carburetor it is better to drain the carburetor bowl using a spanner with a rag/cloth underneath to absorb the small amount of fuel that drains out. Additionally, if you are using the outboards regularly you probably don't need to worry about draining the fuel at all. Cheers

Flushing outboard motors

By: on 1 November 2018
I have been flushing religiously using both the ear muffs and a tank ever since new. Boaties should be aware that this is not a guarantee that the impeller will never need replacing. I always check my water tell tale before launching my boat but last time no water was seen. I had to replace the impeller which had sustained enough damage from sand, etc. to render it useless. Cost of the impeller was $25.00 (from Outboard Spares) taking about half an hour which I did myself. It always pays to check for water flow before leaving home or the ramp. Happy boating.

flushing

By: on 1 November 2018
Where does the salt go when flushing in a drum? back into the water and your engine, if flushing in a tank/drum the water must be replaced at least once, preferably twice during the process, you can add a silicone based additive to the final flush thus coating the internal surfaces of the motor, displacing water and providing an oxygen barrier, fabric softner provides a very good additive and cost about 60c per use.

Flushing

By: on 1 November 2018
My Suzy has a flushing port to connect hose to, I then run about 20lts water thru without running motor. Is this method ok, my yamaha had same.

Outboard Spares Response
Thanks for getting in touch. Any type of flushing is better than not flushing the engine out at all. You are best to run the engine while flushing it out to allow the thermostat to open. I don't believe you can do this on the factory fittings, but I may be wrong. Your owners manual will confirm this. Cheers

WILL A HALF 44 GALLON OIL DRUM WORK OK ?

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 .

Camping

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.

Taste the telltail water

By: on 23 May 2017
I let my outboards run with fresh water until I can't taste the salt in the telltail water anymore. Usually about 5-10 minutes.

Outboard Spares Response
Nice one! It definitely is a popular method of knowing you've flushed all the salt out.

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