What makes you think it's coolant? Antifreeze mixed with oil forms a light brown colored mud which will melt the coating on engine bearings and rot rubber radiator and heater hoses making them feel mushy. Water droplets or a milky white liquid deposited on the underside of the oil fill cap is often mistaken for coolant but is usually condensation from too many short trips where the engine doesn't get to full operating temperature. The remedy for that is a good 30 minute trip on the highway once a week. Often this water stays near the top of the engine where it's cooler, and does not drain out during an oil change.
Check the oil level periodically. If condensation is the problem, the level will not rise on the dipstick. If the level rises, suspect a corroded head gasket allowing pressurized coolant to flow into an oil drain back passage or onto the camshaft and down into the oil pan. This would probably be the most likely cause.
If you find oil residue floating in the coolant reservoir, suspect a leak in the transmission cooler inside one tank of the radiator. Your car is much too new for corrosion to cause this yet, but if this is the cause, you will most likely also find that the transmission fluid is a dull light pink, similar to strawberry sherbet, instead of shiny and clear dark red. The pressures in the transmission cooler lines don't go much over 10 psi, and the coolant starts out at 0 psi and goes up to 15 psi when the engine is warmed up, so the fluids both have a chance to mix in both directions.
If you aren't sure of what's getting into the oil, you can have your mechanic pour a small bottle of dye into the coolant reservoir. After driving for a couple of days, he will shine a special black light on the bottom of the oil cap and into the valve cover. If coolant is present, it will show up as bright yellow.
Saturday, November 28th, 2009 AT 3:09 PM