Black residue in coolant resevoir

[bigfords]

Anybody know what would cause a small layer of black residue in the coolant resevoir? It is only above the coolant level, and it feels a little greasy. There does not appear to be any fuel in the coolant. Would it be the slightest bit of compression?

I flushed the coolant pretty hard about 10,000 miles ago.
I put 238/100 injectors in about 3,000 miles ago (did not install new injector cups).

Also to note, when I bought the truck about 15,000 miles ago, I think the residue was there, but I cleaned it all off as best I could during the coolant flush.

thanks!

 

[David N]

I would think that its oil.

 

[bigfords]

Thats possible, but there is Zero oil in the coolant. Nothing floating in the coolant. Just the residue on the sides of the coolant resevoir about the coolant line...

 

[TyCorr]

Well, where would oil go besides the high point in the.cooling system?

Oil cooler most likely...i had the same issue.until I rebuilt my oil cooler. I guess it could.be your injector.cups but I really dont know...

 

[ghohouston]

If it were diesel (injector cups), you would know. There would be a very identifiable layer of diesel on top of the coolant, and eventually, you would overflow the degas bottle. Ive honestly never seen an oil cooler go bad on a 7.3 like they do on 6.0's, but im sure it happens, but either way, youre going to habe a layer sitting on top of the coolant. You could always take a sample and have it analyzed if you cant figure it out

 

[ghohouston]

And yes it COULD be a compression leak, but doubtful

 

[444 ci]

its your oil cooler mine did the same thing. I put on a new oil cooler and no more problems

 

[Arisley]

X3 on the oil cooler.

 

[TyCorr]

My oil temps have dropped 20° since the rebuilt oil cooler. Had the radiator shop boil it out too.

Mine had plugged passages in probably ten of the holes.

 

[space_heretic]

I thought mine was a oil cooler replaced it after repeated flushes maybe 30 it was still in there. Popped drivers side vc found milk on cover. I'd say if you can compression test it do it first. Just incase


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