Here's why and what to do:
* Head Gasket Failure: The head gasket seals the combustion chambers from the coolant passages and the oil passages. If it fails, coolant can leak into the oil, and vice versa. This is the most common cause of coolant in the oil.
* Cracked Cylinder Head: A crack in the cylinder head can also allow coolant to mix with oil. This is less common than a head gasket failure but equally serious.
* Other (less likely) possibilities: While less probable, other possibilities include a cracked engine block (rare but possible, especially with overheating), a faulty intake manifold gasket (less likely to cause significant oil contamination), or a severely worn-out oil cooler (if it's integrated with the coolant system).
What you should do:
1. Stop driving the vehicle immediately. Continuing to drive will cause further damage and potentially lead to a seized engine.
2. Do NOT add coolant or oil. This will only mask the problem and potentially make things worse.
3. Have the vehicle towed to a qualified mechanic. They can perform a proper diagnosis to pinpoint the source of the leak. Common diagnostic methods include:
* Pressure testing the cooling system: This helps identify leaks in the cooling system.
* Oil analysis: Checking the oil for the presence of coolant and other contaminants.
* Compression test: To check for leaks within the combustion chambers.
* Leak-down test: This checks for leaks past the valves and piston rings.
* Visual inspection: Inspecting the engine for obvious signs of leaks.
4. Prepare for potential repairs: A head gasket replacement or cylinder head repair is a significant undertaking, involving considerable labor and parts costs.
Ignoring this problem will lead to increasingly severe damage, eventually resulting in engine failure. Prompt professional attention is crucial.
