Just bought a '99 Camaro. Checked radiator overflow.. didn't expect a dipstick.. the bottom of it had a dark oily substance on it. Checked radiator under cap.. a bit oily and rusty. Car runs fine.. haven't lost any oil.. any ideas?

 

antifreeze has gone bad. better double flush it and clean the overflow.

 

Thank you I'll give it a try

 

Yup, not to worry, it's not motor oil like most folks think , just crappy coolant. Like Craby says, best to flush it best you can.