I was changing my serpentine belt on my 7.3 and when I was draining the coolant I saw black spots in the coolant. At the bottom of the bucket their seem to be a lot. Should I be very concerned about this and what could that be oil or fuel.

 

Most likely it the Oil cooler leaking oil into the coolant side of the cooler. Could be just bad O rings, Or crack in the cooler.

 

oil = oil cooler- fuel = injector cups. You will know if it's fuel by the smell.

 

new oil cooler orings are in the near work line up.

 

Oil or fuel would float in coolant. If they're at the bottom of the bucket it might just be drop-out from the coolant, or SCA in the coolant. Does it look like sand particles?
This is normal, but not great for the cooling system. A coolant filter would help greatly if this is the case.

 

What Tyler said. If it inks, it's sediment from the casting or the coolant is breaking down if it is the green type. If it is floating, then it is fuel or oil.

 

Hate to ask the obvious but was it a nice clean and dry bucket to start with

 

Every thing was clean I dried that was left and found sludge and metal shavings but no fresh oil so fuel. Where do you guy think the metal in the coolant side could come from.

 

I am going to flush all old coolant out this week

 

Impeller rubbing on the front cover...if it's aluminum shavings.

 

I was thinking the same thing. I wonder if those metal shavings can be picked up with a magnet.

 

I see a water pump in the near future if it's metal shavings.

 

I see a water pump NOW if it's aluminum shavings.

 

That and I see a coolant filter too!

 

International wp with filter built in would be my suggestion.