# Cleaning Water Passages in Engine Block



## fishwhistle (May 26, 2020)

Long story short, I've recently acquired a new to me LT25 with a 08' Mercury 25 EFI. Previous owner lived off St. Johns River and said she rarely saw salt water. On the water test she pee'd ok and functioned well enough for me to buy the boat. 

The past couple weekend trips have seen the pee go from weak, to trickle, to non-existant. I swapped out the impeller yesterday, everything looked well enough. Minimal corrosion and wear on previous impeller. I swapped it out anyway, new gaskets and key too. Get her back together drop into my trashcan of water and still cannot get her to pee.

I spent last night researching these motors and reviewing schematics. This morning I took off the thermostat, gas cooler, and the vapor separator assembly. This pic is what I saw. Doesn't look good. Thermostat looked rough but still functions after placing in boiling water (going to replace either way).

All that said, how would y'all go about cleaning out the internal water passages in the block? I've seen a couple threads about vinegar flushes, Salt-Away, and even pressure washing backwards though the water intake system with the lower unit taken off. I'm not scared of the vinegar knowing I'd flush it out immediately, but would that even have an affect on salt scaling this bad?

Any help is appreciated


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## Smackdaddy53 (Dec 31, 2012)

Remove water passage covers and use Star Brite hull bottom spray and a brass brush. Don’t let the solution sit long or it will eat your aluminum. Rinse off quickly after scrubbing.
Internal passages that you can’t reach are tough but highly concentrated SaltAway or Salt Terminator will help break the crud up. Once you get everything clean, make sure you use the flushing solution after every trip and I mean flush the same day, don’t let the engine sit overnight then do it.


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## fishwhistle (May 26, 2020)

Smackdaddy53 said:


> and I mean flush the same day, don’t let the engine sit overnight then do it.


Thanks smack. I'm religious about flushing on my LT15 with SaltAway through the Yamaha F20. I naively thought others would be the same way...


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## DuckNut (Apr 3, 2009)

If it is not aluminum you can dilute muriatic acid (pool acid) and it will clean it up in a minute.

Once a year I run mine in a tub of water with CLR mixed in - run the discharge stream back into the bucket. Run for a bit turn off let it cool down - do 2-3 times and rinse with clean water- then change your impeller.


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## emptysea (Jul 14, 2019)

Vinegar or salt away.


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## Smackdaddy53 (Dec 31, 2012)

DuckNut said:


> If it is not aluminum you can dilute muriatic acid (pool acid) and it will clean it up in a minute.
> 
> Once a year I run mine in a tub of water with CLR mixed in - run the discharge stream back into the bucket. Run for a bit turn off let it cool down - do 2-3 times and rinse with clean water- then change your impeller.


Star Brite hull cleaner is diluted muratic acid. You can use it on aluminum but have to rinse very quickly or it will eat it. A Yamaha tech buddy taught me this trick years back. I did this on my 70 and it’s been cherry since.


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## Capnredfish (Feb 1, 2012)

🧨


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## Jred (Sep 22, 2013)

Run this through your engine mixed with water. id do more research to find a good mix ratio but i did it to an old Yamaha saltwater series that would overheat all the time and it worked really well


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## Smackdaddy53 (Dec 31, 2012)

Jred said:


> Run this through your engine mixed with water. id do more research to find a good mix ratio but i did it to an old Yamaha saltwater series that would overheat all the time and it worked really well


You didn’t add a link


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## permitchaser (Aug 26, 2013)

When I got my " low hours" motor I noticed it wasn't peeing good so I saw a story on vinegar. I got a big tub, put the foot in and out 5 gallons of vinegar with water, then ran the engine. A bunch of sandy gritty stuff came out. Then I had to run wire through the outer water channels to clear the grit out. It's been working great for 4 years. I'm getting a new impeller put in next week


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## Jred (Sep 22, 2013)

Smackdaddy53 said:


> You didn’t add a link


Biodegradable Marine Descaler & Cleaners - RYDLYME Marine my bad lol


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## Jred (Sep 22, 2013)

Here’s how to use it for an outboard https://www.rydlymemarine.com/wp-content/uploads/2019/12/Outboard_Instructions917.pdf


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## Smackdaddy53 (Dec 31, 2012)

Jred said:


> Biodegradable Marine Descaler & Cleaners - RYDLYME Marine my bad lol


Looks promising. A gallon is about $30


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## Smackdaddy53 (Dec 31, 2012)

The internal passages have a coating that resists scale and salt buildup but after as many years as some of our outboards have this coating deteriorates through so many heat cycles.


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## TroutNreds12 (Jan 4, 2016)

Jred said:


> Here’s how to use it for an outboard https://www.rydlymemarine.com/wp-content/uploads/2019/12/Outboard_Instructions917.pdf


This stuff works awesome I’ve used it a few times even makes engine run cooler afterwards


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## fishwhistle (May 26, 2020)

I wanted to report back in case anyone else has the "ohh-sh*t" moment like I did Saturday morning when I started this post. Thank you to everyone for the tips. @permitchaser I'm curious to know where your buying these large quantities of vinegar.

I ended up picking up West Marine brand "descaler" that was recommended to me by the store manager as an equal to a SaltAway. Also it was only $24/gallon.









I started with about 1/3 of the descaler jug and a couple squirts of CLR mixed in with 20 gallons of fresh water and let my motor idle for 15 mins x 5 times Saturday. With about an hour between each run. The label reads that it doesn't harm rubbers or plastics so I let the motor set over night in the mix. Sunday morning I ran her on idle for 15 mins giving her a couple revs to 2000+ rpm. All sorts of black muck and sand trickled out. I repeated the 15 min idle in clean water for 7-8 more times throughout the day. More and more crap came out and the pee stream slowly gained in volume and pressure. I think the secret was re-circulating the same water, since it keeps the water warm recirculating to break up whatever's up in the block.

This morning I turned her over and she pee'd immediately. Let her idle for an hour with no issues. Need a new thermostat to come in and I'll be back on the water.


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## MMc (Sep 27, 2018)

How did the thermostat housing look after using the descaler?


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## fishwhistle (May 26, 2020)

MMc said:


> How did the thermostat housing look after using the descaler?


I ran all the above cycles with the old thermostat (after removing and cleaning corrosion build up off of it). See my first post pic for the tstat water passage looked like before cleaning. I put the old tstat back in there after cleaning and did all the above cleaning cycles.

When I went to install the new tstat, the same cylinder was notably cleaner and had virtually no corrosion or build up. I will say there was some minor pitting. I don't have a picture but have since put 60+ hours on the motor with no issues. I've ran the descaler about once a month. Flushed with fresh water after every trip.

Does that answer your question?


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## Jason M (Aug 13, 2017)

Dumb question but can you redirect the telltale to stream the water back into the bucket?


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## MMc (Sep 27, 2018)

fishwhistle said:


> I ran all the above cycles with the old thermostat (after removing and cleaning corrosion build up off of it). See my first post pic for the tstat water passage looked like before cleaning. I put the old tstat back in there after cleaning and did all the above cleaning cycles.
> 
> When I went to install the new tstat, the same cylinder was notably cleaner and had virtually no corrosion or build up. I will say there was some minor pitting. I don't have a picture but have since put 60+ hours on the motor with no issues. I've ran the descaler about once a month. Flushed with fresh water after every trip.
> 
> Does that answer your question?


Yes, thanks for the reply. I am a little concerned about it pitting the aluminum over time so I may start with something more mild and resort to this if need be. Glad to know it worked for you.


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## fishwhistle (May 26, 2020)

@Jason M I'm sure you can rig something up, i just put a second 5 gallon bucket to catch the stream and emptied back into the trashcan over the foot of the motor as needed

@MMc I don't think the descaler caused the pitting, but the salt/corrosion certainly did. All things being equal, you shouldn't let your outboard's block get so dirty to a point that it pits. The places where the water channel were pitted were where the corrosion was the worst.


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