Black/Gray water drained from 4.3L Mercrusier---what is the cause?

[denhajm]

I recently winterized my engine block and manifolds. When draining the water out by removing the brass plugs on either side of the block, the water that drained out was not at all clear, but rather was blackish/grayish in color. This is my 3rd winterization season with this boat/engine and I've not seen this before. The boat does occasionally see saltwater use and is raw water cooled. I immediately looked at the oil on the oil dipstick and it looks perfect with no evidence of water/moisture/contamination. Any thoughts on the dark water? It was not rusty brown or orange in color, it was black/gray. '90 SeaRay BR200 with Mercruiser 4.3L and Alpha 1 Drive.

Thanks,

Jason in WA State

 

[RogersJetboat454]

How long was the water sitting in the engine since it was last used? If it's been there for a while, may just be cruddy looking water from sitting in an iron block.
Iron rust isn't always red either. There's such a thing a black oxide.

Also, you may be seeing some sand/silt that had been sitting in the bottom of the water jackets of the block. Opening up the drains, and allowing the water to pass through the bottom liberated the trapped silt.

Just my .02?

 

[denhajm]

Thanks for your reply RogersJetboat454. The water in the engine had sat for quite a while prior to draining. Maybe 6+ weeks?

 

[Bondo]

Ayuh,.... I agree with RJB,... motor block coolin' passages are a poor place to store Clean water, as it's rarely Clean,....

 

[Scott Danforth]

you did flush after your salt water use, correct.

what you see coming out of the block is normal for water sitting in iron. just like you never want to be in a building when the sprinklers go off. the water is not clean like the movies. it is black from iron oxide and bacteria and comes out smelling like a sewer.