Why would there be engin oil in the radiator fluid?

Hi

Most often engine oil escaping into in the coolant is a sign of a failed headgasket. This gasket sits between the cylinder head and the engine block. Combustion pressures can push oil or exhaust gasses into the coolant through the gasket if it has failed or the cylinder head itself has become warped.

There are other rarer possibilities e.g. if your vehicle is fitted with oil coolers these can rupture and send engine oil or transmission fluid into the coolant. However this is least likely to be a cause.

Either way oil in coolant is an indicator of serious mechanical problem and I would recommend that you have your vehicle examined as soon as possible by a mechanic to avoid further costly damage occurring.

Thanks for using FixYa.

Because your head gasket is shot, and needs to be replaced ASAP before you blow the engine.