So I just picked up this truck last night, when I inspected it I saw no leaks. I took it for a ride for a few minutes, then when I returned and let it sit I still found no leaks. After driving it home 2.5 hours, then driving it a few miles today and parking it, I found a puddle of coolant underneath. On top of that the check engine light is now on. Figures all of this happens once I take it home having paid pretty much 100% of the blue book value. Any idea where I should start looking for leaks. Attaching a picture to better illustrate where the leak is coming from underneath.. (Drivers side under engine) The previous owned mentioned that he had a radiator replaced somewhat recently..

 

I'd check the oil cooler and its lines. It's a round oil filter looking thing on the side of the engine about a foot aft of the actual oil filter with hoses to the cooling system.