expading tank got oil and slurge in it?

it will depend what sort of motor you have but you probably have oil in your coolant which could come from a number of sources,does it have an oil cooler? have seen these causing the problem you describe,major problem is to remove the slurry from the coolant system and it will need a detergent to flush out the system,run it for a day or two,drain and refill again and repeat the process until you have the system well flushed out,it may have affected some coolant hoses and these would need replaced also

cdc
November 2010