1998 Dodge Neon oil in the water

When I went to check the coolent level 3 days ago I opened the cap and I noticed there was oil in the water so I drained the water out and refilled it and drove it one more day. I just bought the car off a personal seller and the coolent cap and the oil fill cap are so close together on this car so I just wanted to see if maybe the last person accidently put oil in the water. But it doesn't seem to be the case. Also wen driving it the heat gage will jump all the way to hot for a minute then go back to normal but the car doesn't seem to be overheating. And there doesn't seem to be water in the oil.