1. Intake manifold gasket: The intake manifold gasket is located between the intake manifold and the cylinder heads. If this gasket is damaged or cracked, it can allow coolant to leak into the oil.
2. Oil cooler: The oil cooler is a heat exchanger that helps to cool the engine oil. If the oil cooler is damaged or cracked, it can allow coolant to leak into the oil.
3. Cylinder head: Although you mentioned the head gasket is not the cause, it's still worth inspecting the cylinder head itself for any cracks or damage that could be allowing coolant to leak into the oil.
4. Block porosity: In rare cases, the engine block itself may have porosity, which can allow coolant to seep into the oil passages. This is more common in older engines with high mileage.
To diagnose the exact source of the leak, it is recommended to have a qualified mechanic inspect the engine and pinpoint the location of the leak. This may involve visual inspection, pressure testing, or other diagnostic procedures. Once the source of the leak is identified, the necessary repairs can be made to stop the coolant from leaking into the oil.
