Oil in airtanks.

@AModelCat

 

Looks like engine oil. I would pull the discharge line off the compressor and see if there is fresh oil there. Chances are its the compressor. Unfortunately, you'll more than likely need a new air dryer cartridge as well if the compressor is passing oil.

 

Might just be leftover from what mechanic put in. I’d put some more air brake conditioner in it. They say not to use alcohol, but I have plenty of times. Pour it right into the steel braided line off compressor, so it gets through the whole system. Drain tanks some more till they look fairly clean. I don’t drain my tanks regularly to be honest. When I do, they’re often a little cruddy. All kinds of milky or oily junk come out.

 

I would recommend if you choose to add alcohol to do it into the line coming OUT of the air dryer.

Alcohol is pretty tough on the desiccant cartridges from what I've been told.

 

I would get after fixing what is causing the oil in your air system, likely the compressor but could be a few other things.

Usually when the tanks let crap like that out my wintertime air issues won't be solved till the whole air dryer gets replaced after the new compressor.

 

Your truck may have wabco air drier. I would not worry about this. Just keep letting it out. Summertime it may stop.