A 2001 Astra 1.7DTI, 95k, with nothing at all known about its recent history, seems to run OK (not tried it on a run) but its coolant is black and has an oily feel.
What would you do?
Leave it alone and hope for the best?
Straight coolant change, and see what happens?
Flush it out first? What with? A good squirt of Fairy Liquid and run till hot? Dishwasher detergent?
Stick it straight on ebay?
TIA
Albert