Coolant in oil

I left my truck sit when we had cold weather. It was fine when I parked it. I tried to start it when it warmed up outside and it ran really bad for about 10 seconds and I shut it off. I then saw water in my oil. not milky brown just under the oil in the pan I drained it and all the water came out first and then just oil not mixed but both in the pan, again not milky at all. I disconnect my coolant tank and my oil cooler lines and put the hose to the reservoir line . No more oil filled in the engine or pan and it just came out the oil cooler lines.should I assume at this point it is likely the oil cooler?