Possible Causes:
* Fuel Injectors: A leaking fuel injector is a very common culprit. Fuel under pressure can seep past the injector seals and into the cylinder, then eventually into the crankcase via the piston rings. This often leads to a rich fuel smell in the oil and a milky appearance.
* Fuel Pressure Regulator: This regulator controls fuel pressure in the system. A faulty regulator can allow fuel to leak into the intake manifold vacuum system, then into the crankcase via the PCV system.
* Intake Manifold Gasket: A leak in this gasket can allow fuel to get into the engine's vacuum system and subsequently into the oil.
* Cracked/Porous Cylinder Head: Less common, but possible. A crack in the cylinder head could allow fuel to seep into the engine's cooling system or oil passages. This usually leads to a milky appearance in the oil as well as potentially in the coolant.
* Valve Seals: Less likely, but possible, especially if the truck has high mileage. Worn valve seals could allow fuel to leak past the valves into the combustion chamber, then down into the oil pan.
Diagnostic Steps (Beyond what the dealer should have done):
1. Visual Inspection: Look for any signs of fuel leaks around the fuel injectors, fuel rail, and intake manifold. Carefully examine the intake manifold gasket.
2. Compression Test: This will reveal if the engine has any internal damage like worn piston rings or valve issues. Low compression in one or more cylinders could indicate a problem.
3. Leak-Down Test: More thorough than a compression test, this can pinpoint the source of a leak within each cylinder, identifying worn piston rings or leaky valves.
4. Fuel Pressure Test: Measure fuel pressure to determine if it's within the specifications. This helps rule out a faulty fuel pressure regulator.
5. Oil Analysis: Send an oil sample to a lab for analysis. This will check for the presence of fuel, and may reveal other problems like excessive wear.
6. Cylinder Leak Test: A more specialized test to locate leaks between cylinders (often indicating head gasket problems).
7. Inspect PCV System: The Positive Crankcase Ventilation system is responsible for venting crankcase gases. A blockage or malfunction could cause pressure buildup, pushing fuel into the oil.
Important Considerations:
* Don't drive the truck until the problem is fixed. Driving with gas in the oil can seriously damage the engine.
* Get a second opinion from a different mechanic: Find a reputable independent mechanic specializing in older vehicles, or one with experience in diagnosing fuel-related issues. Explain the dealer's inability to find the problem.
* Document everything: Keep records of all repairs, diagnostics, and communications with the dealer and the new mechanic.
Finding the source of gas in the oil requires a methodical approach. The dealer's inability to diagnose the problem suggests they may have missed some crucial steps. The above steps will help you (or a new mechanic) locate the root cause and fix it before serious engine damage occurs.
