Sooty buildup in thermo housing

[beruken]

While I have a good amount of corrosion, I noticed my thermo housing had an awful lot of what appears to be exhaust soot as opposed to just rust. Black as a sheep. Now this doesn't make sense to me and last year it started easily after a couple seasons down time. No water in the oil that I recall.
1999 4.3 mercuiser
190 sea ray.

 

[dubs283]

Nice!

Reversion, maybe?

Post some pics

 

[chs marine service]

are you sure its soot and not belt shredding? is it all over the alternator as well?

you should have zero exhaust fumes in the engine bay

 

[kenny nunez]

If it is belt dust then the pulleys are probably rusted and the flame arrestor needs cleaning.

 

[chs marine service]

If it is belt dust then the pulleys are probably rusted and the flame arrestor needs cleaning.

agreed

 

[beruken]

If it is belt dust then the pulleys are probably rusted and the flame arrestor needs cleaning.

This is internal to the thermo housing. Mostly within the larger connection. I cleaned out a lot of it already but you can still see some and it's not just a rusted orange mess as usual. I was covered in it like brake or exhaust dust. Due to the advanced corrosion on a couple of the hose connectors I purchased a new one but curios as to the cause.
No, the alternator was not covered really any more than a light coating as usual. I removed the manifolds and noted a small trickle of rust leading into one of the exhaust ports. Engine started fine despite that so I am assuming no compromise there. Boat has been sitting for 2 years so maybe just advanced rust with the water jacket exposed for that time? Thanks for your responses.

 

[dubs283]

Yep, that's a raw water cooled thermostat housing

Debris over the years? Anything the pump receives for supply will make it through the motor if the system is sound

 

[flashback]

Yep rust isn't always red.. might want to investigate the integrity of the housing..