Where is the salt hiding?

[MattFL]

I've been using my 6HP Tohatsu in salt and despite my best efforts to flush and rinse it, after it dries I get salt crystals appearing on the seam between the lower unit and leg, and around the ring that holds the gears in the gear case. I've never had this issue with any other motor, can anyone suggest where the salt might be hiding? I removed the cover and rinsed it from top to bottom, then ran it for 15 minutes in a tub of water that was deep enough to just cover the top exhaust ports right under the power head (I'm really trying to go overboard with rinsing at this point). I ran it around 2000rpm so it got hot enough to open the thermostat. I even put it in and out of the tub a few times to try to rinse the leg out, yet still I get these crystals the next day after it dries off (see attached image).

 

[pvanv]

Probably need to change the rinse water. The flushing plug works well.

 

[dingbat]

Looks more like crevice corrosion than salt residue

 

[MattFL]

Looks more like crevice corrosion than salt residue

Based on how much rinsing and flushing I did with clean water from the hose, this is a possibility, though it happens very fast, within 24 hours of being flushed, which is what made me think salt crystals. If it is corrosion, the next question is why is it happening and how to stop it? The motor has zincs and is stored in a dry air conditioned garage when not in use.

 

[dingbat]

Based on how much rinsing and flushing I did with clean water from the hose, this is a possibility, though it happens very fast, within 24 hours of being flushed, which is what made me think salt crystals. If it is corrosion, the next question is why is it happening and how to stop it? The motor has zincs and is stored in a dry air conditioned garage when not in use.

I suspect if you took the it apart you would find failing (filiform corrosion) and or chipped paint. Moisture trapped in between the parts set off a molecular chain of events that results in what you see.

http://www.drivealuminum.org/wp-content/uploads/2017/02/1page_Corrosion-Types_Automotive.pdf

 

[MattFL]

The more I see it, the more I'm thinking it's salt. It's just popping up in too many places, including around the rubber plug in the opening that you use to disconnect the shift shaft. The motor is a few calendar years old but is mechanically nearly brand new with just under 60 hours, had never seen salt until a couple of weeks ago and even the paint on the prop is still flawless. The water pump impeller is 2 years old so I'll use that as an excuse to take it apart and see what I can find.

 

[w2much]

Use salt away or some vinegar in the tub of water.

 

[MattFL]

Quick follow up; I dropped the lower unit to change the water pump just as part of maintenance, and the leg was very salty inside, the drive shaft was crusted in salt. Despite being flushed in a tub of fresh city water that had the water level above the top exhaust ports. I also changed the thermostat and inside the power head was spotless. It got run hard in the salt and I'm thinking that the salt water which went out with the exhaust coated the inside of the leg from the top down, but in the bucket it doesn't get run hard enough to get a significant amount of fresh water going out the exhaust so all that salt up high in the leg doesn't get flushed out. Does anyone know if buying the flush fitting and using the flush port under the powerhead would do a better job at blowing more fresh water out with the exhaust?