This should not be so hard to figure out but I am trying to determine the leak before I start trying tearing into things that do not need to be fixed. It seems to be the consistency of engine oil but it must be mixing with something else. I saw a green center in a drip of oil this morning and thought maybe the radiator fluid was leaking. It leaks pretty heavily but none of my fluids are showing in loss when as I check them past 500 miles since I first noticed it. There is also no sign of coolant in my engine oil.

 

do you have a tool to pressure test the cooling system to determine where the leak is?

 

could be a mix of coolant and oil, coolant can leak from the heater core connections on the engine compartment side and the "half-moon" between the head and valve cover are notoriously bad for leaking. Get a flexible light and a little mirror and look between the engine and the firewall.

 

there is a plate on the back of the head that can leak coolant and like rowdy said, the half moon rubber piece for the valve cover can leak if you dont silicone em in (recommend toyota FIPG silicone). that would give you the oil coolant mix.

 

well what you have to ask is if its form the motor or the housing? is your truck an automatic or manual. because it could be the gear oil from your tranny if it manual.