What Sand And Weed Can Do To Your Outboard

Author: Stuart Buckingham   Date Posted:30 January 2018 

Blog What sand and weed can do to your outboardAs we all know, our rivers, bays, seas and oceans all consist of various environments. Environments can be anything from sand, rock, weed, gravel, mud and so on. When operating our vessels, large or small, in these environments we need to be mindful of any risks we may be exposing our outboards to and how to avoid potential damage.


Culprit: Sand, Rock and Gravel

Damage: You can get propeller or gearbox impact damage from rock and gravel but where constant dredging of sand is not uncommon you do increase your risk of overheating your engine. Sand and gravel are experts at finding their way into your cooling galleries and blocking them up.


When working for a marine dealer years ago I remember a customer coming in very unhappy that his engine had broken down on him whilst being on holiday at Mallacoota (North East Vic) when he had it serviced a few weeks prior to his trip. His engine overheat alarm was constantly going off even though the water pump and thermostat assembly were recently replaced. Removing the gearbox found that the water pump was fine, however, when the thermostat cover was removed we found the entire thermostat housing and surrounding galleries were chock full of sand and gravel. It was like concrete. The bewildered owner couldn't believe what had occurred but later on acknowledged it probably happened when he was trying to get the boat off the trailer at a shallow sandy ramp on his first day.


Culprit: Weed

Damage: Won’t necessarily block the cooling galleries on the outboard but more so destroys water pumps and impellers. Ribbon weed (or similar seaweed) can be a problem in both shallow and deep waters, where it floats in thick clumps. It can block the intake on the gearbox housing that feeds the water pump restricting the water flow and causing the water pump housing to have insufficient lubrication for the impeller. The end result is a damaged impeller and/or complete water pump.


Getting stuck on a sandbank, driving through shallow channels, launching at a shallow or sandy/rocky boat ramp or driving through a patch of weed all seem harmless enough but all of these can cause damage to varying degrees.


Following the channel markers, trimming your outboard up and keeping an eye out for any changes in the environment you're operating your boat in is the best way of avoiding potential damage to the cooling components of your outboard. That doesn't mean you have to putt around at 5 knots but, just keep an eye out for the risks and avoid them where possible.


To shop our range of thermostats click here or impellers and water pump kits click here.

Comments (3)


By: on 31 January 2018
Just had to replace the impeller and thermostat in grandsons 4 hp Yammie. The thermo was a real disaster, clogged to the max with sand and other rubbish. The young bloke blamed his father for going over sand spits etc, but they are both to blame. After some hours and replacements, all going well now. Given the motor has not many hours on it i could throttle them both. It pays to keep an eye on the tell tail and from reports online, small Yamaha motors are prone to not put out a lot of water at the best of times.

tap/town water

By: on 30 January 2018
Be warned that flushing you're outboard with tap water for 20 years does the same sort of thing as sand/gravel. I have just done the painstaking process of taking the thermostat out to find that wasn't our overheating problem it was deeper, has taken two days to clean the calcium deposits out of the cooling system and now to see if that has fixed the overheating. Water pump was done less than 6 months ago when I did the leg service, so that's not the problem unless its a fauty one.

over heating outboard

By: on 30 January 2018
my yamaha 70hp overheating alarm was going off everytime i went out on the water , i removed the cylinderhead and found that the cooling fins were blocked, i have since cleaned the head and have had no more trouble.

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