HiCustomer Thank you for asking your question on Just Answer.
Have you verified that what you have is actually oil from the engine?
What it could be is that there is transmission fluid in there. This is possible because the transmission fluid runs through an internal tank in the radiator, and that tank could be leaking into the radiator.
I would check the transmission fluid, as soon as possible, to make sure that there is no coolant in the transmission. That would be bad news for the transmission.
Otherwise, these engines are known for having intake manifold gaskets that leak, both internally and externally. But that usually gets antifreeze in the oil, as you mentioned, not the other way around.
Please let me know what you find.
Take Care, Greg A.
There is no oil going through the lower intake manifold, but when the gaskets go, the oil or coolant can leak across the edges. Usually, since the coolant is at higher pressure than the oil, the coolant gets into the engine.
But check this out, which I found while researching this. I found this in the "Cooling System Description" section for the engine.
Engine Oil Cooler The engine oil cooler is a heat exchanger. It is located inside the left side end tank of the radiator. The engine oil temperature is controlled by the temperature of the engine coolant that surrounds the oil cooler in the radiator.
The engine oil pump, pumps the oil through the engine oil cooler line to the oil cooler. The oil then flows through the cooler where the engine coolant absorbs heat from the oil. The oil is then pumped through the oil cooler return line, to the oil filter, to the engine block oil system.
So that is another suspect.