Im having coolant problems?

2000 trans am. it has a dipstick for the return jug. in the jug the coolant looks like oil and feels like oil but smells like normal. in the radiator its completely normal. the previous guy said that he dint know that he was suppose to put dex-cool in and he put 50/50. so there is both. but said that wouldnt do anything. what does this mean?