A method of modifying the oil cooling system of a diesel engine includes the steps of removing the original equipment liquid-to-liquid heat exchanger and installing a manifold having a configuration adapted to match the mounting configuration of the oil passages of the original equipment liquid-to-liquid heat exchanger. The manifold has an oil outlet port directed to a remotely mounted oil cooler. The manifold also has a water passage having a configuration that is adapted to match the mounting configuration of the water passages of the original equipment liquid-to-liquid heat exchanger. The water passage causes the entirety of the flow of water to be discharged back to the water cooling system of the engine where it is circulated by the water pump through the water cooling passages in the engine.