Have you discovered oil mixed with coolant in your car's radiator? You don't have to be a professional auto mechanic to know that these fluids shouldn't mix together. Coolant is designed to stay inside your car's cooling system, whereas oil circulates through the engine's crankcase and its components. If your car's oil and coolant are mixing together, it typically indicates a problem. And to protect your car from failure, you must diagnose and fix this problem.
Why Oil and Coolant Mixing Together Is a Problem
Assuming there are only a few drops of oil in your coolant, you can probably still drive your car -- at least for a while. If you discover large amounts of oil in your coolant, however, continuing to drive could cause catastrophic damage to your car's engine. When large amounts of oil enter your car's cooling system and mix with the coolant, there's less oil to lubricate the engine, which can lead to a blown rod or bearing.
Furthermore, oil doesn't remove heat as effectively coolant. As oil mixes with your car's coolant, you may discover the temperature gauge creeping up into the red zone.
Blown Head Gasket
A blown head gasket is a common cause of oil mixing with coolant. This thin sheet of metal sits between the engine block and cylinder head to create an air-tight and liquid-tight seal. If it fails, oil and coolant may mix together. In some cases, coolant will enter the oil. In others, oil will enter the coolant. When the head gasket fails, you can expect other symptoms to occur as well, such as loss of coolant or white smoke from your tailpipe.
Cracked Engine Block
A cracked engine block can also cause oil to mix with coolant. Allowing your car's engine to overheat even just once can stress it enough to develop hairline cracks. The crack may not be noticeable when inspecting your engine from the outside. Nonetheless, it may allow oil and coolant to mix together, resulting in an oily sludge at the top of your radiator.
Leaking Radiator Oil Cooler
Does your car's radiator have a built-in oil cooler? If so, you should consider having it inspected to ensure that it's not leaking. All radiators hold coolant, but some have a separate compartment for oil. Transmission oil, for example, may travel through a radiator's oil cooler to protect the transmission from overheating. If there's a crack in the oil cooler, transmission oil may leak into into the coolant compartment.