2004 Yamaha T50 TLRC Internal Corrosion

JDusza

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Apr 21, 2009
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I just took apart a T50TLRC that had very bad water in the oil; runny mayonnaise. What I found when I pulled the head was horrible. The internal corrosion looked like the engine had run in salt water. The problem is the cylinder walls are so thin at the head interface that a head gasket has no chance of sealing.
The owner assures me he bought the rig new and it has only seen fresh water.
What would cause such significant internal corrosion in fresh water? Could a neglected overheat cause this?
Thanks,
J
 

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dingbat

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What would cause such significant internal corrosion in fresh water? Could a neglected overheat cause this?
Calcium deposits from “hard” water. Same stuff that builds up on the inside of hot water tanks and recirculating systems over time.
Increasing the water temp would increase the rate of deposit as would low pH of the water.
 

99yam40

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maybe I need more chemical training, because I do not see how hard water deposits would eat the aluminum away
 

dingbat

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maybe I need more chemical training, because I do not see how hard water deposits would eat the aluminum away
The acidity or alkalinity of the environment significantly affects the corrosion behavior of aluminum alloys.

Aluminum oxide (aluminum’s protective coating) is insoluble in a pH of 4-8. Outside this range, aluminum oxide becomes soluble and quickly starts to deteriorate.

Aluminum oxide is quite resistant to concentrated nitric acid. But when exposed to alkaline conditions, corrosion of the oxide film is accelerated, and where the oxide film has been breached, the underlying aluminum is attacked even more aggressively, rapidly resulting in pitting.

In acidic conditions, the oxide is more rapidly attacked than the under laying aluminum and a more generalized attack results.

Acidification (natural and man made) events of our lakes and rivers are common. Would be interested to hear where this guy boats.
 

racerone

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I have a similar 50 HP Yamaha parts motor.----Fresh water.-----Exact same corrosion issue.------Never saw this damage on Johnson / Evinrude from same bodies of water !!!!----So there must be lots more of the Yamaha motors with the same issue.
 

JDusza

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Thank you.
Helps me push a used-power-head-option off the table.
I've heard of the same on a Honda...
So it seems that an "end of year flush" would not help the situation either as the engine remains docked through the season.
Thank you, again,
J
p.s., by the way, Holland, MA. I-84 at CT line. Hamilton Reservoir.
 
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dingbat

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I have a similar 50 HP Yamaha parts motor.----Fresh water.-----Exact same corrosion issue.------Never saw this damage on Johnson / Evinrude from same bodies of water !!!!----
I’ve fought this very same issue in the cooling systems of our equipment for years. Some customers have constant ours others not so much.

Known variables…..temperature, water chemistry, dissimilar metals, ground potentials and the alloy.

After a little research it’s a known issue with pre-2006 Yamaha outboards. Appears to be traced back to a dissimilar metals issue
 

racerone

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But when these engines are docked there should be no water in them.-----A mystery as to why this occurs when engine is running or humid conditions while stopped.-----Hopefully they are using better alloys today.
 

dingbat

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But when these engines are docked there should be no water in them.-----A mystery as to why this occurs when engine is running or humid conditions while stopped.-----Hopefully they are using better alloys today.
I would seriously doubt it’s an alloy issue. Very well studied and understood even back in the early 80’s when I worked on a project with Alcan, now Novelis studying the feasibility of using aluminum in automotive under carriages.

Problem you run into is aluminum’s reactivity to a number of stimulus. The stars line up and poof.

Something as simple as leaving the plastic isolation washer off a copper thermo-coupler could set off a chain of events.
 

racerone

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But I have never seen this type of corrosion on Evinrude / Johnson !!!
 

99yam40

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The acidity or alkalinity of the environment significantly affects the corrosion behavior of aluminum alloys.

Aluminum oxide (aluminum’s protective coating) is insoluble in a pH of 4-8. Outside this range, aluminum oxide becomes soluble and quickly starts to deteriorate.

Aluminum oxide is quite resistant to concentrated nitric acid. But when exposed to alkaline conditions, corrosion of the oxide film is accelerated, and where the oxide film has been breached, the underlying aluminum is attacked even more aggressively, rapidly resulting in pitting.

In acidic conditions, the oxide is more rapidly attacked than the under laying aluminum and a more generalized attack results.

Acidification (natural and man made) events of our lakes and rivers are common. Would be interested to hear where this guy boats.
are you saying that the freshwater lake he runs the motor in is likely outside the PH of 4-8?
 
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