Honda 200hp outboard

There is so much oxidisation on the cooling passages of my engine that the water is unable to circulate. My mechanic says he is locating a mild acid to flush it out, but there is a concern that this step may itself cause corrosion damage.

Is there any treatment for this condition? The engine overheats within minutes of firing her up.

I haven't had the boat long so I can blame the previous owner for not flushing regularly, for all the good that does.

I would really appreciate any advice or guidance - thank you!

Charles

I've heard that a diluted nitric acid mixture works well, but I've never tried it. Search this forum and spend some time on the Internet to see what others have been successful using.

I think the flushing is pretty important. I have over 2000 hours on my 2007 BF225 in saltwater and have not had any corrosion issues. I flush it religiously after every use for at least 15 minutes. I've crafted an extension to the flush hose so that I can connect it with a quick-connect from the deck.

Reading your thread it my be that you have impeller problems i don,t know , if you have blockage problems due to salt build up i would remove the gearbox plug the impeller inlet tube ,remove the thermostat mix the nitric acid to a strong solution with water pour it in through the thermostat and leave it in for a few hours.

Would that solution then simply drain out of the block ?------What keeps that solution from draining out ?

One CAUTION about using nitric acid.
I've been seeing statements made about nitric acid not reacting with aluminium. This is NOT true! Nitric acid can and will desolve aluminum.

Nitric acid is so powerful an oxidant that when a solution of 67% pure or greater contacts aluminium, an immediate and strong reaction takes place. This powerful reaction instantly forms a thin, hard, protective coating on the metal preventing any further chemical reaction between the acid and the aluminum.

Diluting the nitric acid below the 67% threshold COULD cause excessive reaction between the acid and aluminum due to the protective coating not forming.

So, if you use nitric acid to clean aluminium, you should NOT dilute the solution and only use an acid that is 67% pure or purer.

As an aside, a 67% solution can be made with some basic ingredients and rudimentary tools in anyone's kitchen . There are many tutorials on the web.

If you mess around in ANY WAY with nitric acid, PLEASE wear eye protection!!

Its interesting to know why Boeing Aircraft Manufactures in the USA use it before they spray the aluminium , ive experimented with my formula for over 3 years before i used it and my photos prove my results .You can buy it in 70% strength as well a lower strength . you are correct when you say wear eye protection as well as gloves . always ask for the safety data sheet and read it .

racerone said:

Would that solution then simply drain out of the block ?------What keeps that solution from draining out ?

Click to expand...

Providing your thermostat is at the top of the block like the 130hp the thermostat cap has a dome in it as the thermostat opens the water then goes up into the dome and out the hole , so what you do to flush it out once you finished is simply connect a hose to the tube at the bottom by the gearbox and leave the thermostat out for the time being make sure you put the cap back on , or put the gear box back on take the thermostat out connect flush muffs and start the motor once you finished put the thermostat back .This method to flush the motor will only work if your thermostat is on the top of the block.

You could flush two different ways. Run the engine in 55 gallon drum and try to circulate liquid agent or drop the lower unit and fill the block then flush with water. When dropping the lower unit you will have to plug the lift tube, this will allow agent to stay inside the block for a period of time of you determine. Probably have to plug stream as well. This will ensure your concoction won't just run out the block. Remove the T'stats and fill block that way.

If it were me, I would try to scrape some of the corrosion out and run a bench-test on it with vinegar, CRL, Barnacle Buster or other liquid agents. Also, I would grab an o-ring or similar gasket material and a zinc and see how the agent would effect it. Last thing you want is to replace all the soft goods or internal zincs (seals, gaskets, hoses, etc) around the block because some acid disintegrated them.

Over on the Hull Truth, or maybe this forum, I think guys have used Barnacle Buster with decent results. No sure what it is made of but worth investigating. Good luck.

Thanks everyone for your replies - much appreciated!

Charles