There are a few possible ways that oil can get into the coolant system. One possibility is that the head gasket is blown. The head gasket is a seal between the engine block and the cylinder head. If it fails, it can allow oil to leak into the coolant system. Another possibility is that the oil cooler has failed. The oil cooler is a device that helps to cool the engine oil. If it fails, it can allow oil to leak into the coolant system.
The mechanic will need to inspect the car to determine the source of the oil leak. Once the source of the leak has been identified, the mechanic can recommend the appropriate repairs.
In some cases, it may be possible to repair the leak without having to remove the engine. However, in other cases, it may be necessary to remove the engine in order to access the source of the leak.
The cost of repairing an oil leak in the coolant system can vary depending on the source of the leak and the extent of the damage. However, it is important to have the leak repaired as soon as possible to avoid further damage to the engine.