red oily looking substance in expansion tank

What is your question?

I am leaving town and just checked my coolant to make sure I had pleanty. When I took off the cap, the coolant was all the way to the top and a reddish oily substance is floating on top. There was also some gunkie yellowish substance on the cap itself. A few weeks ago I had to have the tensioner pulley and V belts replaced. What is wrong?