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Discussion Starter · #1 ·
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
Mercury Tstat hole.jpg
 

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Zephyr Cove is on FIRE!
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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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Brandon, FL
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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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Zephyr Cove is on FIRE!
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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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I Love microskiff.com!
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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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Zephyr Cove is on FIRE!
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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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I Love Skinny Water
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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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Zephyr Cove is on FIRE!
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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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Discussion Starter · #16 ·
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.
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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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