I have to ask. Is there an
oil cooler that is water/
oil?
I have seen
oil/air oil coolers set up to put the oil through a heat exchanger in the radiator to heat the oil back up if it is too cold when it comes out of the oil/air cooler.
I have also seen oil/water heat exchanger right at the oil filter on the newer Modular engines.
Might be worth tracing out all the external oil lines and water lines.