When mixed with coolant in the radiator it tends to look like a chocolate milkshake.
When engine oil turns gray or milkey cream color, its a sign of moisture in the oil.
the cylinder head has damaged the oil from the engine going to radiator
If it is a pink color then the Transmission cooler is bad in the radiator, If it is oil for sure then the engine oil cooler that's in the radiator may be leaking oil into the radiator. It would really help to know the year ,engine size and what you are working on. The above info may not pertain to your vehicle. Need to ask your question again with all information. THANK YOU NEUTZ.
You have water in your oil. Possibly from condensation. Run the engine only long enough to warm the oil and change it.
If your vehicle has an engine oil cooler ther will be two hydraulic lines going to each side of your radiator. If there are only lines going to one side of your radiator, then it doesn't have an engine oil cooler.
Do you need to check two possibilites, one, check if the oil is from transmission or from the engine, if the oil is red,is from transmission and you need to replace radiator, if the oil if from the engine you got it a big problem, because the only way that the engine oil is inside the radiator is because the engine has a bad head gasket, that mean you need to repair the engine heads.
I believe it is of the same color as land engine oil
Oil, check the dipstick to see if it has the same color, if so , you may need to have engine gasket replacement, or engine structural issues..
you might need to check the water in the batter, engine coolant, radiator, oil.
If its engine oil I would say head gasket or cracked head. Also check under the oil fill cap for a milky color. You can also run the car a few minutes remove the radiator cap see if it smells like gas . Most shops use what they call a sniffer but, Ive found that I can smell the exhaust in the radiator. More than likely head gasket answer is the car automatic? if it is , have your radiator checked to see if transmission fluid is leaking into radiator from oil tank at bottom of radiator if it is engine oil and not transmission oli, you have a cracked head allowing oil to seep into the water chamber a bad head gasket allows water into engine oil, not oil into water
You did not say what you are working on, YEAR AND ENGINE SIZE. But in most cases or designs the water pump can not leak oil into the coolant. The water pump has nothing to do with the engine oil. Does the engine have a engine oil cooler on it ? That would be 2 oil lines just above the oil filter that runs down the side of the engine oil pan a go to the radiator. There are tubes inside of the radiator that oil flows through and they are none to leak oil into the engine coolant that's inside of the RADIATOR. If they are leaking then REPLACE RADIATOR. BUT like I said I don't know what you are working on. Would like to help you with your problem, But need more INFO. NEUTZ.
bad head gasket