Here are the most probable causes:
* Incorrectly installed head gasket: The head gasket has specific orientations and locations for coolant passages, oil passages, and combustion chambers. An incorrectly installed gasket will allow fluids to mix. This is the most likely culprit. The gasket's surface needs to be perfectly clean and flat; imperfections would lead to leaks.
* Damaged engine block or cylinder head: During the head gasket replacement, the engine block or cylinder head may have been cracked or damaged. This could create a pathway for fuel to enter the oil system.
* Fuel pressure regulator failure (less likely): While less likely given the scenario, a failed fuel pressure regulator *could* potentially introduce fuel into the crankcase, but this usually manifests as a fuel smell and isn't directly related to a head gasket job. However, if the job involved working near the fuel system, it's worth considering.
* Fuel injector leak (less likely): An injector leak *could* contribute to fuel in the oil, but this too would likely be noticed before the head gasket job.
What you MUST do:
1. Do NOT attempt to start the engine. This will cause catastrophic damage.
2. Drain the oil completely: Remove all the gasoline-contaminated oil from the oil pan. Dispose of it properly according to local regulations – it's hazardous waste.
3. Inspect the head gasket very carefully: Make absolutely sure it's correctly installed and the engine surfaces are clean and flat. Even a tiny imperfection can cause a leak.
4. Inspect the cylinder head and engine block for cracks: Carefully examine both surfaces for any cracks or damage.
5. Pressure test the cooling system: This can help identify leaks between the cooling system and the oil system.
6. Consult a qualified mechanic: This situation requires the expertise of someone experienced with engine repair. Trying to diagnose and fix this yourself, given the level of complexity, could lead to further damage and significant expense.
This isn't a minor problem; it's a serious one that requires professional attention. Ignoring it will likely result in a destroyed engine.
