Coolant filled oil pan

I suspect we have a warped head or head gasket that has failed. Take a look at these guides that cover this information. I would suggest we start with a compression check to find out if we have a sound engine or what cylinders are suspect. Let me know if you have questions. Thanks

https://www.2carpros.com/articles/coolantantifreeze-in-the-engine-oil

https://www.2carpros.com/articles/head-gasket-blown-test

https://www.2carpros.com/articles/how-to-test-engine-compression

I would like to add that the truck has been sitting , and not running. When I put the coolant in the reservoir it immediately went through and out the oil pan. Immediately, like no resistance with the truck off and not even warm. Would this indicate a head gasket? Or cracked block? Could it possibly be a leaky gasket at the water pump? Up until I parked it a year ago. It was running without overheating or white smoke. It hasn't even been started in over a year. For it to go directly to the engine literally as I poured the coolant in.

Yeah. This would indicate a connection between the head and block that is not supposed to be there. This is most likely a head gasket that is allowing a coolant passage access to the cylinder and the coolant is just pouring past the rings and piston into the oil pan.

I would run a compression check and I am sure you will find the issue.