Q: Can a bad water pump cause water in the oil

Hi and thank you for your question. Water pumps are designed to pump water through the engine, radiator, and heating system. Water pumps will not cause oil to enter the cooling system. The oil coming into the water can be caused by three different things.

First, since you have an automatic transmission, the transmission fluid is cooled by the radiator. The radiator could have broke inside causing the oil to mix in the cooling system. To see if the radiator is the problem, pull the dipstick to the transmission and check the oil. If the oil is milky, then the radiator is your problem.

The second way oil can mix with coolant is though the timing cover. The cover could have caused corrosion and ate though to the water pump’s gallery. This will make the coolant mix with the oil.

The third way that oil can mix with the coolant is when the engine has blown a head gasket. However, if the head gasket is blown, the engine may overheat and have loss of power. I would check the water in the radiator, oil in the engine, and the oil in the transmission.

If you are still having trouble, I would recommend having a local expert inspect the fouled oil and proceed with any repairs that are needed.