2003 Mercury Mountaineer Cream like foam underneath engine

My son in law just purchased this vehicle and has a 60 warranty on it. Truck runs out good so far but we serviced the engine and noticed a cream foam under the oil fill cap and a little down the neck of the fill pipe. Old oil removed seem normal in color. We only serviced oil, oil filter and air filter. Cooling system water is clean and pink. Anything we should be looking out for or we can do. PVC maybe?Thanks in advance for your answer. Ray